Coral trout
Encyclopedia
The coral trout, leopard coral grouper, or leopard coral trout (Plectropomus leopardus) is a species of fish
in the Serranidae
family. Native to the western Pacific Ocean, its natural habitat
includes open sea
s and coral reef
s. Coral trout are piscivorous; juveniles mostly eat crustacean
s, especially prawns, and adults feed upon a variety of reef fish, particularly damselfish
.
Coral trout are the favorite target fish for all sectors of the fishery because they are a good food fish and command high market prices locally and overseas. The total commercial catch of coral trout was reported at over 1500 tonnes in 1998.
), which are all characterized by having three spines on the gill
cover and a large mouth lined with more than one row of sharp teeth.
, Australia
, Brunei
, Cocos (Keeling) Islands
, Fiji
, Hong Kong
, Indonesia
, Japan
, Malaysia, Micronesia
, New Caledonia
, Northern Mariana Islands
, Palau
, Papua New Guinea
, the Philippines
, Samoa
, Singapore
, Solomon Islands
, Taiwan
, Thailand
, Vietnam
,and Egypt
. Its natural habitat
includes open sea
s and coral reef
s. Studies suggest that coral trout move around considerably within a single reef, though often no further than 500 metres (1,640.4 ft) from it. Movement between neighboring reefs does not occur to a large extent; however, there have been a few cases where fish have moved from one reef to another. Much of this movement may be the result of fish moving towards or away from spawning
sites.
Coral trout are protogynous hermaphrodite
s. They start their lives as females and change sex later in life. The trigger of this sex change is unknown. On average, sex change occurs when fish are between 23 centimetres (9.1 in) and 62 cm (24.4 in) in length; the average length at sex change is 42 centimetres (16.5 in). This is believed to happen most frequently in the months immediately following spawning.
ELF research has determined that the sex ratio
differs in different areas of the Great Barrier Reef
, and may differ between reefs opened and protected from fishing. Sex ratios are an important consideration for management, as changes could seriously affect reproduction and thus the number of juveniles coming into the fishery
in future years. All length classes of fish may have both male and female individuals. However, small fish are generally females, while most large fish are males.
Coral trout generally aggregate (crowd into a dense cluster) to spawn. These aggregations are formed around reef slopes around 10 metre deep and peak at the new moon
. Spawning occurs when the tidal flow is strong, particularly during ebb tides. This is thought to allow the newly released eggs to be transported well away from the reef and its associated predators. Spawning typically takes place at dusk, when the light levels make it difficult for predators to see and feed upon the eggs.
s' darkened edges, which can be switched on and off almost instantly. The male will approach a female, which is usually close to the bottom, with his body tilted at 45°–90° (almost lying on his side in the water) and repeatedly quivering lengthwise and shaking his head from side to side. He passes close to the female's head or body with either the top or underside of his body. This process is repeated.
The spawning of coral trout generally occurs over a 30-40 minute period during sunset. Some coral trout (especially males) spawn more than once during an evening.
Fertilization takes place after spawning; the fertilized eggs float just below the water surface. The incubation period for coral trout eggs is unknown, but may be around 20 to 45 hours (the incubation period in related species). The newly hatched larvae are not very well developed and obtain nutrients from a yolk sac
. As the develop, their spines, fins, gut, and other internal organs develop, as do their senses. Eventually, the yolk sac is completely absorbed and the larvae begin to see and catch their own prey.
Growth rates of coral trout are variable; every age class has a wide range of sizes. To estimate growth, the age and size of a fish must be determined. Most commonly, the growth of fish is measured by collecting individuals of varying sizes, measuring their length and determining their age by the otoliths.
Recent research at Bramble Reef has found that common coral trout (P. leopardus) reaches a maximum age of 16 years.
s (fish-eating predators). Younger juvenile trout mostly eat crustacean
s, especially prawns which live on or near the reef bottom. However, adults feed upon a variety of reef fish. The most common type of fish eaten is damselfish
(family Pomacentridae), particularly the spiny chromis damselfish (Acanthochromis polyacanthus
). Adult coral trout also eat juveniles of their own species
. Individual coral trout usually feed once every 1–3 days, although they may go for many days without feeding. 90% of a prey item will be digested within 24 hours. Coral trout only feed during daylight hours, most often at dusk and dawn.
Coral trout hunt in two different ways: by ambush and by prowling. They use the ambush method to hunt fish that live among the coral on the reef bottom. The trout will hide and remain very still and alert, ready to attack passing prey. The prowling method is used to hunt schooling fish higher up in the water. Here, the trout will move (prowl) slowly towards the prey and attack at great speed.
Individual coral trout have different feeding behaviors, possibly explaining the variability in growth and maturity.
Studies have shown that coral trout in the southern Great Barrier Reef feed mainly on parrot fish (family Scaridae) and hardyhead bait fish (family Atherinidae). The most common prey items further north are the damselfish (Pomacentridae) and fusiliers or banana fish (Caesionidae). One study showed coral trout eating schools of fusilers in summer, and scarids during the winter months. This seasonal variation is quite common in the diet of coral trout due to varying abundances of prey at different times of the year. Trout also tend to eat more food in winter, possibly to increase fat stores in preparation for reproduction in spring.
Harvest
Queensland, Australia has a significant coral trout fishery. Fisher people catch the trout using hand lines and pilchards for bait, operating from small dories or run abouts through out the day then returning to a mother ship where the catch is kept live in bio tanks until the return to Port after several days working at sea.
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...
in the Serranidae
Serranidae
Serranidae is a large family of fishes, belonging to the order Perciformes. The family contains about 450 species of serranids in 64 genera, including the sea basses and the groupers...
family. Native to the western Pacific Ocean, its natural habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
includes open sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
s and coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s. Coral trout are piscivorous; juveniles mostly eat 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, especially prawns, and adults feed upon a variety of reef fish, particularly damselfish
Damselfish
Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...
.
Coral trout are the favorite target fish for all sectors of the fishery because they are a good food fish and command high market prices locally and overseas. The total commercial catch of coral trout was reported at over 1500 tonnes in 1998.
Taxonomy
Initially described by French naturalist Bernard Germain de Lacépède in 1802, the Coral trout belongs to a family of fish known as the Serranidae. This family includes groupers and coral cod (not related to true codCod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...
), which are all characterized by having three spines on the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
cover and a large mouth lined with more than one row of sharp teeth.
Distribution and habitat
The Coral trout is found in the waters around American SamoaAmerican Samoa
American Samoa is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the sovereign state of Samoa...
, 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...
, Brunei
Brunei
Brunei , officially the State of Brunei Darussalam or the Nation of Brunei, the Abode of Peace , is a sovereign state located on the north coast of the island of Borneo, in Southeast Asia...
, 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....
, Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
, 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...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, 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...
, Malaysia, Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
, New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
, Northern Mariana Islands
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...
, Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...
, Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, the 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...
, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
, Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
, 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...
, 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...
, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, 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 –...
,and Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
. Its natural habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
includes open sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
s and coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s. Studies suggest that coral trout move around considerably within a single reef, though often no further than 500 metres (1,640.4 ft) from it. Movement between neighboring reefs does not occur to a large extent; however, there have been a few cases where fish have moved from one reef to another. Much of this movement may be the result of fish moving towards or away from 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...
sites.
Reproduction
Documenting the size and age structures during reproduction of coral trout stocks have been a focus of the ELF Experiment as a major indication of how fish stocks respond to various levels of fishing pressure.Coral trout are protogynous hermaphrodite
Protogynous hermaphrodite
A protogynous hermaphrodite is an animal that begins its life cycle as a female. As the animal ages, based on internal or external triggers, it shifts sex to become a male animal. Many fish, such as the gag grouper, undergo just such a metamorphosis. Male fecundity goes up greatly with age more...
s. They start their lives as females and change sex later in life. The trigger of this sex change is unknown. On average, sex change occurs when fish are between 23 centimetres (9.1 in) and 62 cm (24.4 in) in length; the average length at sex change is 42 centimetres (16.5 in). This is believed to happen most frequently in the months immediately following spawning.
ELF research has determined that the 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....
differs in different areas of the Great Barrier Reef
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
, and may differ between reefs opened and protected from fishing. Sex ratios are an important consideration for management, as changes could seriously affect reproduction and thus the number of juveniles coming into the fishery
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
in future years. All length classes of fish may have both male and female individuals. However, small fish are generally females, while most large fish are males.
Spawning
Like many fish, coral trout spawning corresponds to an increase in water temperature (from 25 to 26.5 °C or 77 to 79.7 F) during late spring. In the northern Great Barrier Reef, coral trout spawn between September and December, whereas in the southern regions where the water is cooler, spawning occurs between October and February. The beginning and end of spawning can vary from year to year as the water temperature varies.Coral trout generally aggregate (crowd into a dense cluster) to spawn. These aggregations are formed around reef slopes around 10 metre deep and peak at the new moon
New moon
In astronomical terminology, the new moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth...
. Spawning occurs when the tidal flow is strong, particularly during ebb tides. This is thought to allow the newly released eggs to be transported well away from the reef and its associated predators. Spawning typically takes place at dusk, when the light levels make it difficult for predators to see and feed upon the eggs.
Courtship
As coral trout aggregate, males establish temporary territories. They then try to entice females into their territories to spawn by means of elaborate courtship displays. As part of this courtship ritual, male coral trout display their finFin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
s' darkened edges, which can be switched on and off almost instantly. The male will approach a female, which is usually close to the bottom, with his body tilted at 45°–90° (almost lying on his side in the water) and repeatedly quivering lengthwise and shaking his head from side to side. He passes close to the female's head or body with either the top or underside of his body. This process is repeated.
Spawning rush
Spawning rushes occur after this courtship behavior, if the female agrees. During a spawning rush, the male and female swim rapidly towards the surface, where they release sperm and eggs into the water as they quickly turn. The cloud of sperm and eggs released during a spawning rush is not easily seen, but its presence can sometimes be noted by the frantic feeding of small plankton-eating fish.The spawning of coral trout generally occurs over a 30-40 minute period during sunset. Some coral trout (especially males) spawn more than once during an evening.
Larvae
Like most reef fish, coral trout have a larval stage where the eggs and larvae develop within the water column, allowing them to disperse to nearby reefs.Fertilization takes place after spawning; the fertilized eggs float just below the water surface. The incubation period for coral trout eggs is unknown, but may be around 20 to 45 hours (the incubation period in related species). The newly hatched larvae are not very well developed and obtain nutrients from a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. As the develop, their spines, fins, gut, and other internal organs develop, as do their senses. Eventually, the yolk sac is completely absorbed and the larvae begin to see and catch their own prey.
Growth and lifespan
The fastest period of growth in coral trout occurs in the first three years of life. The average daily growth of newly settled juveniles has been measured at 0.81 mm per day. This means they reach close to 14 cm (5.5 in) in the first 6 months.Growth rates of coral trout are variable; every age class has a wide range of sizes. To estimate growth, the age and size of a fish must be determined. Most commonly, the growth of fish is measured by collecting individuals of varying sizes, measuring their length and determining their age by the otoliths.
Recent research at Bramble Reef has found that common coral trout (P. leopardus) reaches a maximum age of 16 years.
Diet
Coral trout are piscivorePiscivore
A piscivore is a carnivorous animal which eats primarily fish. Piscivory was the diet of early tetrapods , insectivory came next, then in time reptiles added herbivory....
s (fish-eating predators). Younger juvenile trout mostly eat 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, especially prawns which live on or near the reef bottom. However, adults feed upon a variety of reef fish. The most common type of fish eaten is damselfish
Damselfish
Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...
(family Pomacentridae), particularly the spiny chromis damselfish (Acanthochromis polyacanthus
Acanthochromis polyacanthus
Acanthochromis polyacanthus, the spiny chromis damselfish, is a damselfish from the Western Pacific. It occasionally makes its way into the aquarium trade. It grows to a length of ....
). Adult coral trout also eat juveniles of their own species
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
. Individual coral trout usually feed once every 1–3 days, although they may go for many days without feeding. 90% of a prey item will be digested within 24 hours. Coral trout only feed during daylight hours, most often at dusk and dawn.
Coral trout hunt in two different ways: by ambush and by prowling. They use the ambush method to hunt fish that live among the coral on the reef bottom. The trout will hide and remain very still and alert, ready to attack passing prey. The prowling method is used to hunt schooling fish higher up in the water. Here, the trout will move (prowl) slowly towards the prey and attack at great speed.
Individual coral trout have different feeding behaviors, possibly explaining the variability in growth and maturity.
Studies have shown that coral trout in the southern Great Barrier Reef feed mainly on parrot fish (family Scaridae) and hardyhead bait fish (family Atherinidae). The most common prey items further north are the damselfish (Pomacentridae) and fusiliers or banana fish (Caesionidae). One study showed coral trout eating schools of fusilers in summer, and scarids during the winter months. This seasonal variation is quite common in the diet of coral trout due to varying abundances of prey at different times of the year. Trout also tend to eat more food in winter, possibly to increase fat stores in preparation for reproduction in spring.
Harvest
Queensland, Australia has a significant coral trout fishery. Fisher people catch the trout using hand lines and pilchards for bait, operating from small dories or run abouts through out the day then returning to a mother ship where the catch is kept live in bio tanks until the return to Port after several days working at sea.