Giant trevally
Encyclopedia
The giant trevally, Caranx ignobilis (also known as the giant kingfish, lowly trevally, barrier trevally, ulua, or GT), is a species
of large marine
fish
classified in the jack family, Carangidae
. The giant trevally is distributed throughout the tropical waters of the Indo-Pacific
region, with a range stretching from South Africa
in the west to Hawaii
in the east, including Japan
in the north and Australia
in the south. The giant trevally is distinguished by its steep head profile, strong tail scute
s and a variety of other more detailed anatomical features. It is normally a silvery colour with occasional dark spots, however males may be black once they mature. It is the largest fish in the genus Caranx
, growing to a maximum known size of 170 cm and a weight of 80 kg
. The giant trevally inhabits a wide range of marine environments, from estuaries, shallow bays and lagoon
s as a juvenile to deeper reef
s, offshore atoll
s and large embayments as an adult. Juveniles of the species are known to live in waters of very low salinity
such as coastal lakes and upper reaches of rivers, and tend to prefer turbid waters.
The giant trevally is a powerful apex predator
in most of its habitats, and is known to hunt individually and in schools. The species predominantly takes various fish as prey, although crustacean
s, cephalopod
s and molluscs make up a considerable part of the diet in some regions. The species has some quite novel hunting strategies including following monk seals and stealing prey that is stirred up, as well as using shark
s to ambush prey. The species reproduces in the warmer months, with peaks differing by region. Spawning
occurs at specific stages of the lunar cycle, when large schools of giant trevally congregate to spawn over reefs and bays, with reproductive behaviour observed in the wild. The fish grows relatively fast, reaching sexual maturity
at a length of around 60 cm at 3 years of age. The giant trevally is both an important species to commercial fisheries and a recognised gamefish, with the species taken by nets and lines by professionals and by bait and lures by anglers. Catch statistics in the Asia
n region show hauls of 4000-10 000 tonnes, while around 10 000 lbs
of the species is taken in Hawaii each year. The species is considered poor to excellent table fare
by different authors, although ciguatera
poisoning is common in the fish. Dwindling numbers around the main Hawaiian Islands have also led to several proposals to reduce the catch of fish in this region.
, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae
, a group of percoid
fishes in the order Perciformes
.
The giant trevally was first scientifically described by the Swedish naturalist
Peter Forsskål
in 1775 based on specimens taken from the Red Sea
off both Yemen
and Saudi Arabia
, with one of these designated to be the holotype
. He named the species Scomber ignobilis, with the specific epithet Latin for "unknown", "obscure" or "ignoble". It was assigned to the mackerel genus Scomber
, where many carangids were placed before they were classified as a separate family. This later revision in classification saw the species moved to the genus Caranx, where it has remained. Even after its initial description, the giant trevally (and the bigeye trevally
) were often confused with the Atlantic
crevalle jack
, Caranx hippos, due to their superficial similarity, which led to some authors claiming the crevalle jack had a circumtropical distribution. After Forsskål's initial description and naming, the species was independently renamed three times as Caranx lessonii, Caranx ekala and Carangus hippoides, all of which are now considered invalid junior synonyms. The latter of these names once again highlighted the similarity with the crevalle jack, with the epithet hippoides essentially meaning 'like Carangus hippos, which was the crevalle jack's Latin name at that point in time. Despite the resemblance with the crevalle jack, the two species have never been phylogenetically compared, either morphologically or genetically, to determine their relationship.
Caranx ignobilis is most commonly
referred to as the 'giant trevally' (or 'giant kingfish') due to its large maximum size, with this often abbreviated to simply 'GT' by many anglers. Other names occasionally used include 'lowly trevally', 'barrier trevally', 'yellowfin jack' (not to be confused with Hemicaranx leucurus), Forsskål's Indo-Pacific jack fish and Goyan fish. In Hawaii
, the species is almost exclusively referred to as 'ulua', often in conjunction with the prefixes 'black', 'white', or 'giant'. Due to its wide distribution there are many other names for the species in different languages also.
, greater amberjack
, leerfish and rainbow runner
), with a recorded maximum length of 170 cm and a weight of 80 kg
. Specimens this size are very rare, with the species only occasionally seen at lengths greater than 80 cm. It appears the Hawaiian Islands contain the largest individuals, where indivduals over 100 lbs are common. Elsewhere in the world, only three individuals over 100 lbs have been reported to the IGFA.
The giant trevally is similar in shape to a number of other large jacks and trevallies, having an ovate, moderately compressed body with the dorsal profile more convex than the ventral profile, particularly anteriorly. The dorsal fin
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 18 to 21 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 15 to 17 soft rays. The pelvic fins contain 1 spine and 19 to 21 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head. The lateral line
has a pronounced and moderately long anterior arch, with the curved section intersecting the straight section below the lobe of the second dorsal fin. The curved section of the lateral line contains 58-64 scales
while the straight section contains 0 to 4 scales and 26 to 38 very strong scute
s. The chest is devoid of scales with the exception of a small patch of scales in front of the pelvic fins. The upper jaw contains a series of strong outer canine
s with an inner band of smaller teeth, while the lower jaw contains a single row of conical teeth. The species has 20 to 24 gill raker
s in total and there are 24 vertebrae present.
The eye is covered by a moderately well developed adipose eyelid, and the posterior extremity of the jaw
is vertically under or just past the posterior margin of the pupil. The eye of the giant trevally has a horizontal 'streak' in which ganglion
and photoreceptor cell densities are markedly greater than the rest of the eye. It is believed this allows the fish to gain a panoramic
view of its surroundings, removing the need to constantly move the eye. This in turn will allow easier of detection of prey or predator in that field of view.
At sizes less than 50 cm, the giant trevally is a silvery-grey fish, with the head and upper body slightly darker in both sexes. Fish greater than 50 cm show sexual dimorphism
in their colouration, with males having a dusky to jet black body, while females are a much lighter coloured silvery grey. Individuals with a darker dorsal colouration often also display striking silvery striation
s and markings on the upper part of their body, particularly their back. Black dots of a few millimetres in diameter may also be found scattered all over the body, although the coverage of these dots varies between widespread to none at all. All the fins are generally light grey to black, although fish taken from turbid waters often have yellowish fins, with the anal fin being the brightest. The leading edge and tips of the anal and dorsal fins are generally lighter in colour than the main fin. There is no black spot on the operculum
. Traces of broad cross-bands on the fish's sides are occasionally seen after death.
The giant trevally is widely distributed throughout the tropical and subtropical waters of the Indian
and Pacific Ocean
s, ranging along the coasts of three continent
s and many hundreds of smaller islands and archipelago
s. In the Indian Ocean, the species easternmost range is the coast of continental Africa, being distributed from the southern tip of South Africa
north along the east African coastline to the Red Sea
and Persian Gulf
. The giant trevally's range extends eastwards along the Asia
n coastline including Pakistan
, India
and into South East Asia, the Indonesian Archipelago
and northern Australia
. The southernmost record from the west coast of Australia comes from Rottnest Island
, not far offshore from the capital city of Perth
. Elsewhere in the Indian Ocean, the species has been recorded from hundreds of small island groups including the Maldives
, Seychelles
, Madagascar
and the Cocos (Keeling) Islands
.
The giant trevally is abundant in the central Indo-Pacific region, found throughout all the archipelagos and offshore islands including Indonesia, Philippines
and Solomon Islands
. Along continental Asia, the species has been recorded from Malaysia to Vietnam
, but not China. Despite this, its offshore range does extend north to Hong Kong
, Taiwan
and southern Japan
. In the south, the species reaches as far south as New South Wales
in Australia and even to the northern tip of New Zealand
in the southern Pacific. Its distribution continues throughout the western Pacific including Tonga
, Western Samoa and Polynesia
, with its westernmost limits known to be the Pitcairn and Hawaii
an Islands.
The giant trevally inhabits a very wide range of offshore
and inshore marine environments, with the species also known to tolerate the low salinity
waters of estuaries and rivers. It is a semi-pelagic fish known to spend time throughout the water column, but is mostly demersal in nature.
The species is most common in shallow coastal waters in a number of environments including coral and rocky reef
s and shorefaces, lagoon
s, embayments, tidal flats and channels. They commonly move between reef patches, often over large expanses of deeper sand and mud bottoms between the reefs. Older individuals tend to move to deeper seaward reefs, bombora
s and drop-offs away from the protection of fringing reefs, often to depths greater than 80 m. Large individuals however do often return to these shallower waters as they patrol their range, often to hunt or reproduce. In Hawaii, the juvenile to subadult giant trevally are the most common large carangids in the protected inshore waters, with all other species apparently preferring the outer, less protected reefs. It is also easily attracted to artificial reef
s, where studies have found it to be one of the predominant species around these structures in Taiwan.
Juvenile to sub-adult giant trevally are known to enter and inhabit estuaries, the upper reaches of rivers and coastal lakes in several locations including South Africa, Solomon Islands, Philippines, India, Taiwan, Thailand, northern Australia and Hawaii. In some of these locations, such as Australia, it is a common and relatively abundant inhabitant, while in others including South Africa and Hawaii, it is much rarer in estuaries. The species has a wide salinity
tolerance, as evident from the ranges juvenile and subadult fish in South African estuaries have been recorded from; 0.5 to 38 ‰, with other studies also showing tolerance levels of less than 1 ‰. In these estuaries, the giant trevally is known from both highly turbid, dirty water to clean, high visibility waters, however in most cases the species prefers the turbid waters. It appears younger fish actively seek out these turbid waters, and when no estuaries are present they live in the turbid inshore waters of bays and beach
es. These young fish eventually move to inshore reefs as they mature, before again moving to deeper outer reefs. In the Philippines, a population of giant trevally inhabit (and were once common in) the landlocked fresh waters of Taal lake
, and are referred to as "maliputo" to distinguish them from the marine variant, (locally named "talakitok"). Along with Taal volcano
and Taal lake, the land locked maliputo is prominently featured on the reverse side of the newly redesigned Philippine 50 Peso bill.
, only schooling for the purposes of reproduction and more rarely for feeding. Juveniles and sub-adults commonly school, both in marine and estuarine environments. Observations from South African estuaries indicate the schools of smaller juveniles tend not to intermingle with schools of other species, however larger sub-adults are known to form mixed species schools with the brassy trevally
. As well as the movement between habitats as the species grows, there has also been research conducted on the movements of larger fish around their habitats to understand how marine reserves impact on the species. Adult giant trevally are known to range back and forth up to 9 km along a home range, with some evidence of diel
and seasonal shifts in habitat use. In the Hawaiian Islands it has been shown giant trevally do not normally move between atoll
s, but have specific core areas they spent most their time. Within these core areas, habitat shifts during different times of the day have been recorded, with the fish being most active at dawn and dusk, and usually shifting location near sunrise or sunset. Furthermore, large seasonal migration
s appear to occur for the purpose of aggregating for spawning, with this also known from the Solomon Islands. Despite not moving between atolls, they do make periodic atoll-wide journeys of up to 29 km. Long term studies show that juveniles can move up to 70 km away from their protected habitats to outer reefs and atolls. The giant trevally is one of the most important apex predator
s in its habitats, both as adults on reefs and as juveniles in estuaries. Observations in relatively untouched waters of the Northwestern Hawaiian Islands
showed the giant trevally was of high ecological importance, constituting 71% of the apex predator biomass
, and was the dominant apex predator. This number is considerably less in heavily fishes Hawaiian waters. At smaller sizes, the species is prey to sharks, and large individuals have been recorded as a host of the sharksucker, Echeneis naucrates, a fish which is normally seen attached to the underside of sharks.
The giant trevally is a powerful predatory fish
, and is an apex predator in most environments; from the estuaries it inhabits as a juvenile to the outer reefs and atolls it patrols as an adult. Hunting appears to occur at different times of the day in different areas of its range; off South Africa it is most active during the day, especially at dawn and dusk, while off Zanzibar
and Hong Kong it is said to be nocturnal in its habits. The species diet has been determined in several countries and habitats, with this research finding the diet generally varies slightly between locations and age. In all but one study (which was of juveniles), the giant trevally dominantly takes other fishes, with various crustacean
s, cephalopod
s and occasionally molluscs making the remainder of the diet. In Hawaii the species has a predominantly fish based diet consisting of Scaridae and Labridae, with crustaceans, including lobster
s, and cephalopods (squid and octopus) making up the remaining portion of the diet. The large number of reef fish
es suggests that it spends much of its time foraging over shallow-water reef habitats, but the presence of squid and the schooling carangid Decapterus macarellus indicates exploitation of more open-water habitats as well. Off Africa the diet is similar, consisting mostly of fish including eel
s, with minor squid, octopus, mantis shrimp
s, lobsters and other crustaceans. Younger fish inside Kaneohe Bay, Hawaii showed the only instance when crustaceans were preferred over fish; stomatopods, shrimp
s and crab
s were the most common prey taken at 89% of stomach content by volume, with fish, mostly of the family Blennidae, making up only 7% of the stomach contents. Estuarine fish in both Hawaii and Australia have mostly fish-based diets, with crustaceans such as prawns and amphipods also of importance, and are known to take more novel prey such as spiders and insects in these habitats. There have also been reports of juvenile turtle
s and dolphin
s being found within the stomach contents of larger giant trevally. Studies of different size classes of fish have found the diet does change with age in some locations, with the changes relating to an increased volume of fish taken.
Studies in controlled environments on the giant trevally's feeding strategies have found that hunting in schools increases their capture efficiency, however is not necessary for an individual's survival. When a school is formed during feeding, one individual will take a leading position, with others trailing behind it. Several individuals will attack the prey school, striking and stunning the prey, with the leading individual generally being more successful. Some individuals act individually and opportunistically within the school if one of the prey fish becomes isolated, with the main advantage of schooling appearing to be the ability to further break up and isolate prey schools. The only time hunting in schools is a disadvantage is when only isolated prey are present, such as close to a reef; here an individual hunter has a greater probability of capturing it than if a group is present. Another hunting strategy of the giant trevally is to 'escort' Monk Seals, a behavior which has been observed in the Hawaiian Islands. The trevally swim close by the seal, and when the seal stops to forage, the trevally positions its mouth inches away from the seal. If a prey item is disturbed, the trevally will attempt to steal the prey from the seal, which routinely does occur. The seal does not appear to gain any benefit from this relationship, and it is thought juvenile seals being followed in this way may be outcompeted by the larger fish. A similar strategy has been employed by fish in the presence of large reef shark
s, as they use the larger animal as a tool to ambush prey. The opportunistic nature of giant trevally has also been made evident by studies on the mortality rate
of undersized or egg-bearing lobsters released from traps at the water's surface in the Hawaiian Islands. The fish are efficient predators of these crustaceans, with individuals often seizing a lobster before it could sink to the seafloor after being released, or attacking before the lobster moves into a defensive position. Some bolder large individuals are even known to eat the lobster head first when its in a defensive stance.
The giant trevally (ulua) reaches sexual maturity
at 54 to 61 cm in length and 3 to 4 years of age, although many authors narrow this down to 60 cm and 3 years of age. Sex ratio
estimates from the Hawaiian Islands suggest that the population is slightly skewed toward females, with the male:female ratio being 1:1.39. Spawning
occurs during the warmer months in most locations, although the exact dates differ by location. In southern Africa this occurs between July to March, with a peak between November and March; in the Philippines between December and January with a lesser peak during at June; and in Hawaii between April and November with a major peak during May to August. Lunar cycles are also known to control the spawning events, with large schools forming in certain locations at specific phases of the moon in Hawaii and the Solomon Islands. Locations for spawning include reefs, the reef channels and offshore banks. Sampling of schools prior to spawning suggests the fish segregate into schools of only one sex, although the details of this are still unclear. Observations in the natural habitat found spawning occurred during the day immediately after and just before the change of tide
when there were no currents
. Giant trevally gathered in schools of over 100 individuals, although ripe individuals occurred slightly deeper; around 2 to 3 m above the seabed in groups of 3 to 4, with one silver female being chased by several black males. Eventually a pair would sink down to a sandy bottom, where egg
s and sperm
were released. The fish then diverged and swum away. It appears that that each individual spawns more than once in each period, with only part of the gonad
s ripe in spawners. Fecundity
is not known, although females are known to release several thousand eggs on capture during the spawning process. Eggs are described as pelagic and transparent in nature.
The giant trevally's early larval
stages and their behaviour have been extensively described, with all fins having formed by at least 8 mm of age, with larvae and sub-juveniles being silver with six dark vertical bars. Laboratory populations of fish show a significant variability in the length at a certain age, with the average range being around 6.5 mm. Growth rates in larvae between 8.0 and 16.5 mm are on average 0.36 mm per day. The speed at which larvae swim increases with age from 12 cm/s at 8 mm in length to 40 cm/s at 16.5 mm, with size rather than age a better predictor of this parameter. Size is also a better predictor of endurance in larvae than age. These observations suggest that the species becomes an effective swimmer (is able to swim against a current) at around 7–14 mm. No obvious relationships with age and either swimming depth or trajectory have been found. Larvae appear to also opportunistically feed on small zooplankton
while swimming. The larvae actively avoid other large fish, and jellyfish
are occasionally used as temporary cover. Larvae have no association with reefs, and appear to prefer to live pelagically. Daily growth is estimated at between 3.82 g/day and 20.87 g/day, with larger fish growing at a more rapid rate. Age at 1 year old is 18 cm, age at 2 years is 35 cm and by 3 years, the fish is around 50 to 60 cm. The use of von Bertalanffy growth curves fitted to observed otolith
data shows an individual of around 1 m in length is approximately 8 years old, while a 1.7 m fish would be around 24 years old. The maximum theoretical length of the species predicted by the growth curves is 1.84 m, however the largest reported individual was 1.7 m long. As previously mentioned, as the giant trevally grows it shifts from turbid inshore waters or estuaries to reefs and lagoons in bays, moving finally to outer reefs and atolls.
A hybrid of C. ignobilis and C. melampygus
(bluefin trevally) has been recorded from Hawaii. The specimen was initially thought to be a bluefin trevally of world record size, however was later rejected when it was discovered to be a hybrid. Initial evidence of hybridisation was morphological characteristics intermediate to the two species, with later genetic tests confirmed that it was indeed a hybrid. It is known the two species school together, including at spawning time, which was considered to be the reason for hybridisation.
The giant trevally has been utilised by humans since prehistoric times
, with the oldest known records of the capture of this species by Hawaiians, whose culture
held the fish in high regard. The ulua, as the fish is known to Hawaiians, was likened to a fine man and strong warrior
, which was the cause of a ban on women eating the species in antiquity. The species was often used in Hawaiian religious rites, and took place of a human sacrifice
when none was available. Culturally, the fish was seen as a god
, and treated as gamefish which commoners could not hunt. There are many mentions of ulua in Hawaiian proverb
s, all generally relating to the strength and warrior-like qualities of the fish. The Hawaiians considered the fish to be of excellent quality, with white firm flesh. Despite this, intrusions of giant trevally into modern day fishponds used by Hawaiians for rearing fish are unwelcome, as being a predator it eats more than it is worth at market.
The giant trevally is of high importance to modern day fisheries throughout its range, although quantifying the amounts taken is very difficult due to the lack of fishery statistics kept in most of these countries. Hawaii has the best kept statistics, with the 1998 catch consisted of 10 194 pounds of giant trevally worth around 12 000 US dollars. Historically the species has been taken in far greater numbers, and have been important food, market and game fish since the early 1900s. However their exploitation has seen the landings of the species decrease by over 84% since the turn of the century, declining from 725 000 lb catches to the 10 000 lb catches of recent. FAO statistics of the Asian region record catches between 4000 and 10 000 tonnes between 1997 and 2007, although this excludes most fisheries which are not monitored or don't discriminate between trevally species. The giant trevally is commercially caught by a number of methods including hook and line, including handlines, gill nets and other types of artisanal traps. The species has also successfully been bred for aquaculture purposes in Taiwan. It is sold at market fresh, frozen, salted
, smoked, and as fishmeal and oil
.
The giant trevally is considered one of the top gamefish of the Indo-Pacific region, having outstanding strength, speed and endurance once hooked. It can be taken by many methods, including baits of cut or live fish and squid, as well as a wide array of lures
. The species is commonly taken on bibbed plugs, minnows, spoons, jigs and poppers as well as soft plastic lures and saltwater flies
. In recent years, the development of both jigging and surface-popping techniques have seen the giant trevally become an extremely popular candidate for catch and release fishing, with many charter operators based around this concept. The species is also popular with spearfishermen
throughout its range. The species edibility
has been rated from poor to excellent by different authors, although there are numerous reports of ciguatera
poisoning from the species. Detailed tests on a large (1m) specimen taken from Palmyra Island showed the toxicity of the fish's flesh, liver
and washed intestinal tract produced no or weakly positive symptoms to laboratory mice, however the digested contents of the intestine were lethal. The authors argued that based on this test the flesh of giant trevally was safe to consume. However analysis of case studies in which ciguatera
poisoning was reported after eating the fish suggested that an accumulative effect occurs with repeated consumption; and also that tests like the one outlined above are not reliable, as the toxin appears to be distributed haphazardly throughout each fish. Since 1990, giant trevally taken from the main Hawaiian islands have been blocked from sale by auction internationally due to concerns over liability from ciguatera poisoning.
study in the Hawaiian Islands indicates that the main Hawaiian Islands are heavily depleted in the species, which in untouched ecosystems comprises 71% of the apex predator biomass. In contrast, it comprises less than 0.03% of the apex biomass in exploited habitats, with only a single fish observed during the course of this research study. Prior to this, a 1993 report suggested the population around the main Hawaiian islands were not stressed, even though several biological indicators suggested to the contrary. This was due to the highly size-selective nature of the fishery, which theoretically should prevent a decrease in numbers. Despite this, populations have decreased, and in light of their continued falling abundance in Hawaii, several recommendations including banning the commercial take of the species, increasing minimum lengths and decreasing bag limits for anglers, as well as reassessment of protected areas for the species have been proposed by officials. The species (nor any other carangid) has not been assessed by the IUCN.
Some recreational fishing groups are also promoting a catch and release
practise for the giant trevally, with this becoming an increasingly popular option for charter boat operators, who have also begun to tag giant trevally for scientific purposes. At large sizes, the species is more likely to be ciguatoxic, and therefore if the fish is kept it must be disposed of or sent to a taxidermist if it is a trophy fish. A catch and release approach has also been adopted by operators outside of Hawaii, with Australian operators who target the species by popping and jigging rarely keeping any fish. Careful fish handling techniques have also been implemented by anglers so as not to damage the fish; such techniques include supporting the fish's weight, using barbless single rather than treble hooks and restricting the time the fish spends out the water to a minimum.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of large marine
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
classified in the jack family, Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
. The giant trevally is distributed throughout the tropical waters of the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region, with a range stretching from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in the west to Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
in the east, including Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
in the north and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in the south. The giant trevally is distinguished by its steep head profile, strong tail scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s and a variety of other more detailed anatomical features. It is normally a silvery colour with occasional dark spots, however males may be black once they mature. It is the largest fish in the genus Caranx
Caranx
Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...
, growing to a maximum known size of 170 cm and a weight of 80 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
. The giant trevally inhabits a wide range of marine environments, from estuaries, shallow bays and lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s as a juvenile to deeper reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, offshore atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
s and large embayments as an adult. Juveniles of the species are known to live in waters of very low salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
such as coastal lakes and upper reaches of rivers, and tend to prefer turbid waters.
The giant trevally is a powerful apex predator
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
in most of its habitats, and is known to hunt individually and in schools. The species predominantly takes various fish as prey, although crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s and molluscs make up a considerable part of the diet in some regions. The species has some quite novel hunting strategies including following monk seals and stealing prey that is stirred up, as well as using shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s to ambush prey. The species reproduces in the warmer months, with peaks differing by region. Spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occurs at specific stages of the lunar cycle, when large schools of giant trevally congregate to spawn over reefs and bays, with reproductive behaviour observed in the wild. The fish grows relatively fast, reaching sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at a length of around 60 cm at 3 years of age. The giant trevally is both an important species to commercial fisheries and a recognised gamefish, with the species taken by nets and lines by professionals and by bait and lures by anglers. Catch statistics in the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n region show hauls of 4000-10 000 tonnes, while around 10 000 lbs
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
of the species is taken in Hawaii each year. The species is considered poor to excellent table fare
Fish (food)
Fish is a food consumed by many species, including humans. The word "fish" refers to both the animal and to the food prepared from it. Fish has been an important source of protein for humans throughout recorded history.-Terminology:...
by different authors, although ciguatera
Ciguatera
Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...
poisoning is common in the fish. Dwindling numbers around the main Hawaiian Islands have also led to several proposals to reduce the catch of fish in this region.
Taxonomy and phylogeny
The giant trevally is classified within the genus CaranxCaranx
Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...
, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, a group of percoid
Percoidei
Percoidei is one of eighteen suborders of bony fish in the order Perciformes. Many commercially harvested fish species are contained in this suborder, including the snappers, jacks, whitings, groupers, bass, perches and porgies.-Divisions:...
fishes in the order Perciformes
Perciformes
The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...
.
The giant trevally was first scientifically described by the Swedish naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Peter Forsskål
Peter Forsskål
Peter Forsskål, sometimes spelled Pehr Forsskål, Peter Forskaol, Petrus Forskål or Pehr Forsskåhl, was a Swedish explorer, orientalist, naturalist and an apostle of Carl Linnaeus.-Early life:...
in 1775 based on specimens taken from the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
off both Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....
and Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...
, with one of these designated to be the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
. He named the species Scomber ignobilis, with the specific epithet Latin for "unknown", "obscure" or "ignoble". It was assigned to the mackerel genus Scomber
Scomber
Scomber is a genus of ocean-dwelling mackerels in the family Scombridae.-Species:FishBase lists four species:* Blue mackerel, Scomber australasicus Cuvier, 1832.* Atlantic Chub Mackerel, Scomber colias Gmelin, 1789....
, where many carangids were placed before they were classified as a separate family. This later revision in classification saw the species moved to the genus Caranx, where it has remained. Even after its initial description, the giant trevally (and the bigeye trevally
Bigeye trevally
The bigeye trevally, Caranx sexfasciatus , is a species of widespread large marine fish classified in the jack family Carangidae...
) were often confused with the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
crevalle jack
Crevalle jack
The crevalle jack, Caranx hippos is a common species of large marine fish classified within the jack family, Carangidae...
, Caranx hippos, due to their superficial similarity, which led to some authors claiming the crevalle jack had a circumtropical distribution. After Forsskål's initial description and naming, the species was independently renamed three times as Caranx lessonii, Caranx ekala and Carangus hippoides, all of which are now considered invalid junior synonyms. The latter of these names once again highlighted the similarity with the crevalle jack, with the epithet hippoides essentially meaning 'like Carangus hippos, which was the crevalle jack's Latin name at that point in time. Despite the resemblance with the crevalle jack, the two species have never been phylogenetically compared, either morphologically or genetically, to determine their relationship.
Caranx ignobilis is most commonly
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
referred to as the 'giant trevally' (or 'giant kingfish') due to its large maximum size, with this often abbreviated to simply 'GT' by many anglers. Other names occasionally used include 'lowly trevally', 'barrier trevally', 'yellowfin jack' (not to be confused with Hemicaranx leucurus), Forsskål's Indo-Pacific jack fish and Goyan fish. In Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, the species is almost exclusively referred to as 'ulua', often in conjunction with the prefixes 'black', 'white', or 'giant'. Due to its wide distribution there are many other names for the species in different languages also.
Description
The giant trevally is the largest member of the genus Caranx, and the fifth largest member of the family Carangidae (exceeded by the yellowtail amberjackYellowtail amberjack
The yellowtail amberjack or great amberjack, Seriola lalandi, is a large fish found in the Pacific and Indian oceans. It can be divided into three sub-species: The California yellowtail, Seriola lalandi dorsalis, the southern yellowtail, or in New Zealand and Australia the yellowtail kingfish or...
, greater amberjack
Greater amberjack
The Greater amberjack is a jack of the genus Seriola. It is found in the Mediterranean Sea, the Atlantic Ocean, the Pacific Ocean and the Indian coasts, living usually between 20 and 70 m of depth...
, leerfish and rainbow runner
Rainbow runner
The rainbow runner , also known as the rainbow yellowtail, Spanish jack and Hawaiian salmon, is a common species of pelagic marine fish of the jack family, Carangidae. The species is widespread throughout the tropical and subtropical waters of the world, inhabiting both coastal as well as far...
), with a recorded maximum length of 170 cm and a weight of 80 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
. Specimens this size are very rare, with the species only occasionally seen at lengths greater than 80 cm. It appears the Hawaiian Islands contain the largest individuals, where indivduals over 100 lbs are common. Elsewhere in the world, only three individuals over 100 lbs have been reported to the IGFA.
The giant trevally is similar in shape to a number of other large jacks and trevallies, having an ovate, moderately compressed body with the dorsal profile more convex than the ventral profile, particularly anteriorly. The dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 18 to 21 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 15 to 17 soft rays. The pelvic fins contain 1 spine and 19 to 21 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
has a pronounced and moderately long anterior arch, with the curved section intersecting the straight section below the lobe of the second dorsal fin. The curved section of the lateral line contains 58-64 scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
while the straight section contains 0 to 4 scales and 26 to 38 very strong scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s. The chest is devoid of scales with the exception of a small patch of scales in front of the pelvic fins. The upper jaw contains a series of strong outer canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
s with an inner band of smaller teeth, while the lower jaw contains a single row of conical teeth. The species has 20 to 24 gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
s in total and there are 24 vertebrae present.
The eye is covered by a moderately well developed adipose eyelid, and the posterior extremity of the jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
is vertically under or just past the posterior margin of the pupil. The eye of the giant trevally has a horizontal 'streak' in which ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
and photoreceptor cell densities are markedly greater than the rest of the eye. It is believed this allows the fish to gain a panoramic
Panorama
A panorama is any wide-angle view or representation of a physical space, whether in painting, drawing, photography, film/video, or a three-dimensional model....
view of its surroundings, removing the need to constantly move the eye. This in turn will allow easier of detection of prey or predator in that field of view.
At sizes less than 50 cm, the giant trevally is a silvery-grey fish, with the head and upper body slightly darker in both sexes. Fish greater than 50 cm show sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in their colouration, with males having a dusky to jet black body, while females are a much lighter coloured silvery grey. Individuals with a darker dorsal colouration often also display striking silvery striation
Striation
Striations means a series of ridges, furrows or linear marks, and are used in several ways* Glacial striation* Striation , a striation as a result of a geological fault* In medicine, striated muscle...
s and markings on the upper part of their body, particularly their back. Black dots of a few millimetres in diameter may also be found scattered all over the body, although the coverage of these dots varies between widespread to none at all. All the fins are generally light grey to black, although fish taken from turbid waters often have yellowish fins, with the anal fin being the brightest. The leading edge and tips of the anal and dorsal fins are generally lighter in colour than the main fin. There is no black spot on the operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
. Traces of broad cross-bands on the fish's sides are occasionally seen after death.
Distribution
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, ranging along the coasts of three continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
s and many hundreds of smaller islands and archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
s. In the Indian Ocean, the species easternmost range is the coast of continental Africa, being distributed from the southern tip of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
north along the east African coastline to the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
and Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
. The giant trevally's range extends eastwards along the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n coastline including Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and into South East Asia, the Indonesian Archipelago
Malay Archipelago
The Malay Archipelago refers to the archipelago between mainland Southeastern Asia and Australia. The name was derived from the anachronistic concept of a Malay race....
and northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The southernmost record from the west coast of Australia comes from Rottnest Island
Rottnest Island
Rottnest Island is located off the coast of Western Australia, near Fremantle. It is called Wadjemup by the Noongar people, meaning "place across the water". The island is long, and at its widest point with a total land area of . It is classified as an A Class Reserve and is managed by the...
, not far offshore from the capital city of Perth
Perth, Western Australia
Perth is the capital and largest city of the Australian state of Western Australia and the fourth most populous city in Australia. The Perth metropolitan area has an estimated population of almost 1,700,000....
. Elsewhere in the Indian Ocean, the species has been recorded from hundreds of small island groups including the Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
, Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and the Cocos (Keeling) Islands
Cocos (Keeling) Islands
The Territory of the Cocos Islands, also called Cocos Islands and Keeling Islands, is a territory of Australia, located in the Indian Ocean, southwest of Christmas Island and approximately midway between Australia and Sri Lanka....
.
The giant trevally is abundant in the central Indo-Pacific region, found throughout all the archipelagos and offshore islands including Indonesia, Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
and Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
. Along continental Asia, the species has been recorded from Malaysia to Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
, but not China. Despite this, its offshore range does extend north to Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
and southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. In the south, the species reaches as far south as New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
in Australia and even to the northern tip of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
in the southern Pacific. Its distribution continues throughout the western Pacific including Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
, Western Samoa and Polynesia
Polynesia
Polynesia is a subregion of Oceania, made up of over 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are termed Polynesians and they share many similar traits including language, culture and beliefs...
, with its westernmost limits known to be the Pitcairn and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
an Islands.
Habitat
Shore
A shore or shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In Physical Oceanography a shore is the wider fringe that is geologically modified by the action of the body of water past and present, while the beach is at the edge of the shore,...
and inshore marine environments, with the species also known to tolerate the low salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
waters of estuaries and rivers. It is a semi-pelagic fish known to spend time throughout the water column, but is mostly demersal in nature.
The species is most common in shallow coastal waters in a number of environments including coral and rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s and shorefaces, lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s, embayments, tidal flats and channels. They commonly move between reef patches, often over large expanses of deeper sand and mud bottoms between the reefs. Older individuals tend to move to deeper seaward reefs, bombora
Bombora
Bombora is an indigenous Australian term for an area of large sea waves breaking over a shallow area such as a submerged rock shelf, reef, or sand bank that is located some distance from the shoreline and beach surf break....
s and drop-offs away from the protection of fringing reefs, often to depths greater than 80 m. Large individuals however do often return to these shallower waters as they patrol their range, often to hunt or reproduce. In Hawaii, the juvenile to subadult giant trevally are the most common large carangids in the protected inshore waters, with all other species apparently preferring the outer, less protected reefs. It is also easily attracted to artificial reef
Artificial reef
An artificial reef is a human-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, control erosion, block ship passage, or improve surfing....
s, where studies have found it to be one of the predominant species around these structures in Taiwan.
Juvenile to sub-adult giant trevally are known to enter and inhabit estuaries, the upper reaches of rivers and coastal lakes in several locations including South Africa, Solomon Islands, Philippines, India, Taiwan, Thailand, northern Australia and Hawaii. In some of these locations, such as Australia, it is a common and relatively abundant inhabitant, while in others including South Africa and Hawaii, it is much rarer in estuaries. The species has a wide salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
tolerance, as evident from the ranges juvenile and subadult fish in South African estuaries have been recorded from; 0.5 to 38 ‰, with other studies also showing tolerance levels of less than 1 ‰. In these estuaries, the giant trevally is known from both highly turbid, dirty water to clean, high visibility waters, however in most cases the species prefers the turbid waters. It appears younger fish actively seek out these turbid waters, and when no estuaries are present they live in the turbid inshore waters of bays and beach
Beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
es. These young fish eventually move to inshore reefs as they mature, before again moving to deeper outer reefs. In the Philippines, a population of giant trevally inhabit (and were once common in) the landlocked fresh waters of Taal lake
Taal Lake
Taal Lake is a freshwater lake in the province of Batangas, on the island of Luzon, Philippines. The lake is situated within a caldera formed by very large eruptions between 500,000 and 100,000 years ago. It is the country's third largest lake...
, and are referred to as "maliputo" to distinguish them from the marine variant, (locally named "talakitok"). Along with Taal volcano
Taal Volcano
Taal Volcano is a complex volcano located on the island of Luzon in the Philippines. Historical eruptions are concentrated on Volcano Island, an island near the middle of Lake Taal. The lake partially fills Taal Caldera, which was formed by powerful prehistoric eruptions between 140,000 to 5,380 BP...
and Taal lake, the land locked maliputo is prominently featured on the reverse side of the newly redesigned Philippine 50 Peso bill.
Biology and ecology
The giant trevally is a solitary fish once it reaches sexual maturitySexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
, only schooling for the purposes of reproduction and more rarely for feeding. Juveniles and sub-adults commonly school, both in marine and estuarine environments. Observations from South African estuaries indicate the schools of smaller juveniles tend not to intermingle with schools of other species, however larger sub-adults are known to form mixed species schools with the brassy trevally
Brassy trevally
The brassy trevally, Caranx papuensis is a species of large marine fish classified in the jack family, Carangidae...
. As well as the movement between habitats as the species grows, there has also been research conducted on the movements of larger fish around their habitats to understand how marine reserves impact on the species. Adult giant trevally are known to range back and forth up to 9 km along a home range, with some evidence of diel
Diel
People with the surname Diel:* Charles Diel, former head men’s tennis coach at Louisiana State University* Paul Diel , French psychologistDiel may also refer to:* Diel vertical migration, common among deep-sea fish...
and seasonal shifts in habitat use. In the Hawaiian Islands it has been shown giant trevally do not normally move between atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
s, but have specific core areas they spent most their time. Within these core areas, habitat shifts during different times of the day have been recorded, with the fish being most active at dawn and dusk, and usually shifting location near sunrise or sunset. Furthermore, large seasonal migration
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
s appear to occur for the purpose of aggregating for spawning, with this also known from the Solomon Islands. Despite not moving between atolls, they do make periodic atoll-wide journeys of up to 29 km. Long term studies show that juveniles can move up to 70 km away from their protected habitats to outer reefs and atolls. The giant trevally is one of the most important apex predator
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
s in its habitats, both as adults on reefs and as juveniles in estuaries. Observations in relatively untouched waters of the Northwestern Hawaiian Islands
Northwestern Hawaiian Islands
The Northwestern Hawaiian Islands or the Leeward Islands are the small islands and atolls in the Hawaiian island chain located northwest of the islands of Kauai and Niihau. They are administered by the U.S. state of Hawaii except Midway Atoll, which has temporary residential facilities and is...
showed the giant trevally was of high ecological importance, constituting 71% of the apex predator biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
, and was the dominant apex predator. This number is considerably less in heavily fishes Hawaiian waters. At smaller sizes, the species is prey to sharks, and large individuals have been recorded as a host of the sharksucker, Echeneis naucrates, a fish which is normally seen attached to the underside of sharks.
Diet and feeding
Predatory fish
Predatory fish are fish that predate upon other fish or animals. Some predatory fish include perch, muskie , pike, walleye, salmon.Levels of large predatory fish in the global oceans are estimated to be about 10% of their pre-industrial levels...
, and is an apex predator in most environments; from the estuaries it inhabits as a juvenile to the outer reefs and atolls it patrols as an adult. Hunting appears to occur at different times of the day in different areas of its range; off South Africa it is most active during the day, especially at dawn and dusk, while off Zanzibar
Zanzibar
Zanzibar ,Persian: زنگبار, from suffix bār: "coast" and Zangi: "bruin" ; is a semi-autonomous part of Tanzania, in East Africa. It comprises the Zanzibar Archipelago in the Indian Ocean, off the coast of the mainland, and consists of numerous small islands and two large ones: Unguja , and Pemba...
and Hong Kong it is said to be nocturnal in its habits. The species diet has been determined in several countries and habitats, with this research finding the diet generally varies slightly between locations and age. In all but one study (which was of juveniles), the giant trevally dominantly takes other fishes, with various crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s and occasionally molluscs making the remainder of the diet. In Hawaii the species has a predominantly fish based diet consisting of Scaridae and Labridae, with crustaceans, including lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s, and cephalopods (squid and octopus) making up the remaining portion of the diet. The large number of reef fish
Reef fish
Coral reef fish are fish which live amongst or in close relation to coral reefs. Coral reefs form complex ecosystems with tremendous biodiversity. Among the myriad inhabitants, the fish stand out as particularly colourful and interesting to watch. Hundreds of species can exist in a small area of a...
es suggests that it spends much of its time foraging over shallow-water reef habitats, but the presence of squid and the schooling carangid Decapterus macarellus indicates exploitation of more open-water habitats as well. Off Africa the diet is similar, consisting mostly of fish including eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
s, with minor squid, octopus, mantis shrimp
Mantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...
s, lobsters and other crustaceans. Younger fish inside Kaneohe Bay, Hawaii showed the only instance when crustaceans were preferred over fish; stomatopods, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s and crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s were the most common prey taken at 89% of stomach content by volume, with fish, mostly of the family Blennidae, making up only 7% of the stomach contents. Estuarine fish in both Hawaii and Australia have mostly fish-based diets, with crustaceans such as prawns and amphipods also of importance, and are known to take more novel prey such as spiders and insects in these habitats. There have also been reports of juvenile turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s and dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
s being found within the stomach contents of larger giant trevally. Studies of different size classes of fish have found the diet does change with age in some locations, with the changes relating to an increased volume of fish taken.
Studies in controlled environments on the giant trevally's feeding strategies have found that hunting in schools increases their capture efficiency, however is not necessary for an individual's survival. When a school is formed during feeding, one individual will take a leading position, with others trailing behind it. Several individuals will attack the prey school, striking and stunning the prey, with the leading individual generally being more successful. Some individuals act individually and opportunistically within the school if one of the prey fish becomes isolated, with the main advantage of schooling appearing to be the ability to further break up and isolate prey schools. The only time hunting in schools is a disadvantage is when only isolated prey are present, such as close to a reef; here an individual hunter has a greater probability of capturing it than if a group is present. Another hunting strategy of the giant trevally is to 'escort' Monk Seals, a behavior which has been observed in the Hawaiian Islands. The trevally swim close by the seal, and when the seal stops to forage, the trevally positions its mouth inches away from the seal. If a prey item is disturbed, the trevally will attempt to steal the prey from the seal, which routinely does occur. The seal does not appear to gain any benefit from this relationship, and it is thought juvenile seals being followed in this way may be outcompeted by the larger fish. A similar strategy has been employed by fish in the presence of large reef shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, as they use the larger animal as a tool to ambush prey. The opportunistic nature of giant trevally has also been made evident by studies on the mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
of undersized or egg-bearing lobsters released from traps at the water's surface in the Hawaiian Islands. The fish are efficient predators of these crustaceans, with individuals often seizing a lobster before it could sink to the seafloor after being released, or attacking before the lobster moves into a defensive position. Some bolder large individuals are even known to eat the lobster head first when its in a defensive stance.
Life history
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 54 to 61 cm in length and 3 to 4 years of age, although many authors narrow this down to 60 cm and 3 years of age. Sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
estimates from the Hawaiian Islands suggest that the population is slightly skewed toward females, with the male:female ratio being 1:1.39. Spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occurs during the warmer months in most locations, although the exact dates differ by location. In southern Africa this occurs between July to March, with a peak between November and March; in the Philippines between December and January with a lesser peak during at June; and in Hawaii between April and November with a major peak during May to August. Lunar cycles are also known to control the spawning events, with large schools forming in certain locations at specific phases of the moon in Hawaii and the Solomon Islands. Locations for spawning include reefs, the reef channels and offshore banks. Sampling of schools prior to spawning suggests the fish segregate into schools of only one sex, although the details of this are still unclear. Observations in the natural habitat found spawning occurred during the day immediately after and just before the change of tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
when there were no currents
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
. Giant trevally gathered in schools of over 100 individuals, although ripe individuals occurred slightly deeper; around 2 to 3 m above the seabed in groups of 3 to 4, with one silver female being chased by several black males. Eventually a pair would sink down to a sandy bottom, where egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s and sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
were released. The fish then diverged and swum away. It appears that that each individual spawns more than once in each period, with only part of the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s ripe in spawners. Fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
is not known, although females are known to release several thousand eggs on capture during the spawning process. Eggs are described as pelagic and transparent in nature.
The giant trevally's early larval
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
stages and their behaviour have been extensively described, with all fins having formed by at least 8 mm of age, with larvae and sub-juveniles being silver with six dark vertical bars. Laboratory populations of fish show a significant variability in the length at a certain age, with the average range being around 6.5 mm. Growth rates in larvae between 8.0 and 16.5 mm are on average 0.36 mm per day. The speed at which larvae swim increases with age from 12 cm/s at 8 mm in length to 40 cm/s at 16.5 mm, with size rather than age a better predictor of this parameter. Size is also a better predictor of endurance in larvae than age. These observations suggest that the species becomes an effective swimmer (is able to swim against a current) at around 7–14 mm. No obvious relationships with age and either swimming depth or trajectory have been found. Larvae appear to also opportunistically feed on small zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
while swimming. The larvae actively avoid other large fish, and jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
are occasionally used as temporary cover. Larvae have no association with reefs, and appear to prefer to live pelagically. Daily growth is estimated at between 3.82 g/day and 20.87 g/day, with larger fish growing at a more rapid rate. Age at 1 year old is 18 cm, age at 2 years is 35 cm and by 3 years, the fish is around 50 to 60 cm. The use of von Bertalanffy growth curves fitted to observed otolith
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
data shows an individual of around 1 m in length is approximately 8 years old, while a 1.7 m fish would be around 24 years old. The maximum theoretical length of the species predicted by the growth curves is 1.84 m, however the largest reported individual was 1.7 m long. As previously mentioned, as the giant trevally grows it shifts from turbid inshore waters or estuaries to reefs and lagoons in bays, moving finally to outer reefs and atolls.
A hybrid of C. ignobilis and C. melampygus
Bluefin trevally
The bluefin trevally, Caranx melampygus , is a species of large, widely distributed marine fish classified in the jack family, Carangidae...
(bluefin trevally) has been recorded from Hawaii. The specimen was initially thought to be a bluefin trevally of world record size, however was later rejected when it was discovered to be a hybrid. Initial evidence of hybridisation was morphological characteristics intermediate to the two species, with later genetic tests confirmed that it was indeed a hybrid. It is known the two species school together, including at spawning time, which was considered to be the reason for hybridisation.
Relationship to humans
Prehistory
Prehistory is the span of time before recorded history. Prehistory can refer to the period of human existence before the availability of those written records with which recorded history begins. More broadly, it refers to all the time preceding human existence and the invention of writing...
, with the oldest known records of the capture of this species by Hawaiians, whose culture
Culture
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...
held the fish in high regard. The ulua, as the fish is known to Hawaiians, was likened to a fine man and strong warrior
Warrior
A warrior is a person skilled in combat or warfare, especially within the context of a tribal or clan-based society that recognizes a separate warrior class.-Warrior classes in tribal culture:...
, which was the cause of a ban on women eating the species in antiquity. The species was often used in Hawaiian religious rites, and took place of a human sacrifice
Human sacrifice
Human sacrifice is the act of killing one or more human beings as part of a religious ritual . Its typology closely parallels the various practices of ritual slaughter of animals and of religious sacrifice in general. Human sacrifice has been practised in various cultures throughout history...
when none was available. Culturally, the fish was seen as a god
God
God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....
, and treated as gamefish which commoners could not hunt. There are many mentions of ulua in Hawaiian proverb
Proverb
A proverb is a simple and concrete saying popularly known and repeated, which expresses a truth, based on common sense or the practical experience of humanity. They are often metaphorical. A proverb that describes a basic rule of conduct may also be known as a maxim...
s, all generally relating to the strength and warrior-like qualities of the fish. The Hawaiians considered the fish to be of excellent quality, with white firm flesh. Despite this, intrusions of giant trevally into modern day fishponds used by Hawaiians for rearing fish are unwelcome, as being a predator it eats more than it is worth at market.
The giant trevally is of high importance to modern day fisheries throughout its range, although quantifying the amounts taken is very difficult due to the lack of fishery statistics kept in most of these countries. Hawaii has the best kept statistics, with the 1998 catch consisted of 10 194 pounds of giant trevally worth around 12 000 US dollars. Historically the species has been taken in far greater numbers, and have been important food, market and game fish since the early 1900s. However their exploitation has seen the landings of the species decrease by over 84% since the turn of the century, declining from 725 000 lb catches to the 10 000 lb catches of recent. FAO statistics of the Asian region record catches between 4000 and 10 000 tonnes between 1997 and 2007, although this excludes most fisheries which are not monitored or don't discriminate between trevally species. The giant trevally is commercially caught by a number of methods including hook and line, including handlines, gill nets and other types of artisanal traps. The species has also successfully been bred for aquaculture purposes in Taiwan. It is sold at market fresh, frozen, salted
Salting (food)
Salting is the preservation of food with dry edible salt. It is related to pickling . It is one of the oldest methods of preserving food, and two historically significant salt-cured foods are dried and salted cod and salt-cured meat.Salting is used because most bacteria, fungi and other potentially...
, smoked, and as fishmeal and oil
Fish oil
Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid , and docosahexaenoic acid , precursors of certain eicosanoids that are known to reduce inflammation throughout the body, and are thought to have many health benefits.Fish do not...
.
The giant trevally is considered one of the top gamefish of the Indo-Pacific region, having outstanding strength, speed and endurance once hooked. It can be taken by many methods, including baits of cut or live fish and squid, as well as a wide array of lures
Fishing lure
A fishing lure is an object attached to the end of a fishing line which is designed to resemble and move like the prey of a fish. The purpose of the lure is to use movement, vibration, and colour to catch the fish's attention so it bites the hook...
. The species is commonly taken on bibbed plugs, minnows, spoons, jigs and poppers as well as soft plastic lures and saltwater flies
Fly fishing
Fly fishing is an angling method in which an artificial 'fly' is used to catch fish. The fly is cast using a fly rod, reel, and specialized weighted line. Casting a nearly weightless fly or 'lure' requires casting techniques significantly different from other forms of casting...
. In recent years, the development of both jigging and surface-popping techniques have seen the giant trevally become an extremely popular candidate for catch and release fishing, with many charter operators based around this concept. The species is also popular with spearfishermen
Spearfishing
Spearfishing is an ancient method of fishing that has been used throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks....
throughout its range. The species edibility
Fish (food)
Fish is a food consumed by many species, including humans. The word "fish" refers to both the animal and to the food prepared from it. Fish has been an important source of protein for humans throughout recorded history.-Terminology:...
has been rated from poor to excellent by different authors, although there are numerous reports of ciguatera
Ciguatera
Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...
poisoning from the species. Detailed tests on a large (1m) specimen taken from Palmyra Island showed the toxicity of the fish's flesh, liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and washed intestinal tract produced no or weakly positive symptoms to laboratory mice, however the digested contents of the intestine were lethal. The authors argued that based on this test the flesh of giant trevally was safe to consume. However analysis of case studies in which ciguatera
Ciguatera
Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...
poisoning was reported after eating the fish suggested that an accumulative effect occurs with repeated consumption; and also that tests like the one outlined above are not reliable, as the toxin appears to be distributed haphazardly throughout each fish. Since 1990, giant trevally taken from the main Hawaiian islands have been blocked from sale by auction internationally due to concerns over liability from ciguatera poisoning.
Conservation
A decline in giant trevally numbers around inhabited regions has been well documented in Hawaii, with both catch data as presented above and ecological studies showing this decrease in numbers. A biomassBiomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
study in the Hawaiian Islands indicates that the main Hawaiian Islands are heavily depleted in the species, which in untouched ecosystems comprises 71% of the apex predator biomass. In contrast, it comprises less than 0.03% of the apex biomass in exploited habitats, with only a single fish observed during the course of this research study. Prior to this, a 1993 report suggested the population around the main Hawaiian islands were not stressed, even though several biological indicators suggested to the contrary. This was due to the highly size-selective nature of the fishery, which theoretically should prevent a decrease in numbers. Despite this, populations have decreased, and in light of their continued falling abundance in Hawaii, several recommendations including banning the commercial take of the species, increasing minimum lengths and decreasing bag limits for anglers, as well as reassessment of protected areas for the species have been proposed by officials. The species (nor any other carangid) has not been assessed by the IUCN.
Some recreational fishing groups are also promoting a catch and release
Catch and release
Catch and release is a practice within recreational fishing intended as a technique of conservation. After capture, the fish are unhooked and returned to the water before experiencing serious exhaustion or injury...
practise for the giant trevally, with this becoming an increasingly popular option for charter boat operators, who have also begun to tag giant trevally for scientific purposes. At large sizes, the species is more likely to be ciguatoxic, and therefore if the fish is kept it must be disposed of or sent to a taxidermist if it is a trophy fish. A catch and release approach has also been adopted by operators outside of Hawaii, with Australian operators who target the species by popping and jigging rarely keeping any fish. Careful fish handling techniques have also been implemented by anglers so as not to damage the fish; such techniques include supporting the fish's weight, using barbless single rather than treble hooks and restricting the time the fish spends out the water to a minimum.
External links
- Giant trevally (Caranx ignobilis) at FishBase
- Giant trevally (Caranx ignobilis) at Australian Museum Online
- Giant trevally (Caranx ignobilis) at giant-trevally.com
- Giant trevally (Caranx ignobilis) at Fishing Earth
- Giant trevally (Caranx ignobilis) at GT Popping
- Giant trevally (Caranx ignobilis) at Xtrem-Fishing