Plotosus
Encyclopedia
Plotosus is a genus
of catfish
es (order
Siluriformes) of the family
Plotosidae. It includes six species
, P. canius, P. fisadoha, P. limbatus, P. lineatus, P. nkunga, P. papuensis.
P. canius originates from coastal regions of Thailand
, Sundaland
, Sulawesi
, Moluccas, and India
, and into the lower Mekong River. P. fisadoha is known only from Southeastern Madagascar
. P. limbatus inhabits marine and brackish waters in the Western Indian Ocean
and Arabian Sea
. P. lineatus occurs in the eastern Mediterranean, marine waters in the Indian Ocean and Western Pacific, and sometimes entering freshwaters in East Africa
and Madagascar. P. nkunga is distributed in southern Africa from Boknes to Boteler Point, and possibly to Zanzibar
, in marine waters but also entering freshwater. P. papuensis ranges in the south of the island of New Guinea
.
. P. limbatus grows to 41 cm (16 in) SL
. P. lineatus grows to 32 cm (13 in) TL. P. nkunga grows to about 51 cm (20 in) SL. P. papuensis is recorded to reach 55 cm (22 in) TL, though it may reach 100 cm (40 in) TL according to local fishermen.
All species have been confirmed to be venom
ous except for P. fisadoha. The anterior spines of the dorsal
and pectoral fins can inflict painful wounds. In P. lineatus, the highly venomous serrate spine of the first dorsal and each of the pectoral fins may even be fatal.
The scaleless skin of P. nkunga is coated in mucus
, and its mouth is surrounded by four pairs of sensory barbels
. The spines of the serrated dorsal fin
, which can lock into an erect position, are covered in toxic mucus that can poison humans.
s; it is also found in estuaries, tide pools and open coasts. P. papuensis is found in turbid rivers and swampy lagoons and backwaters.
Juveniles of Plotosus species often form dense aggregations; in P. lineatus juveniles form dense ball-shaped schools of about 100 fish, while adults are solitary or occur in smaller groups of around 20 and are known to hide under ledges during the day.
Most species feed on crustacean
s, mollusks, and fishes. Adult P. lineatus search and stir the sand incessantly for crustaceans, mollusks, worms, and sometimes fish. P. nkunga feeds mainly on benthic invertebrate
s, using its barbels to feel around in the mud for crab and small fish.
P. lineatus is an oviparous
fish; this species has demersal eggs and planktonic larvae.
canals in its electrosensory organs (originally termed "ampullae of Lorenzini", though now the name is not used) as the voltage gradient across the skin is less than in fresh water and so they must extend deeper into the fish where the difference will be more marked in order that the maximal volatage be registered. Such deep canals are found in elasmobranchs, though not in the freshwater stingray Potamotrygon, indicating this time loss of extended canals rather than gain.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
es (order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Siluriformes) of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Plotosidae. It includes six species
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...
, P. canius, P. fisadoha, P. limbatus, P. lineatus, P. nkunga, P. papuensis.
Distribution
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...
, Sundaland
Sundaland
Sundaland is a biogeographical region of Southeastern Asia which encompasses the areas of the Asian continental shelf that was exposed during the last ice age. It included the Malay Peninsula on the Asian mainland, as well as the large islands of Borneo, Java, and Sumatra and their surrounding...
, Sulawesi
Sulawesi
Sulawesi is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the Maluku Islands. In Indonesia, only Sumatra, Borneo, and Papua are larger in territory, and only Java and Sumatra have larger Indonesian populations.- Etymology :The Portuguese were the first to...
, Moluccas, and 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 the lower Mekong River. P. fisadoha is known only from Southeastern Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. P. limbatus inhabits marine and brackish waters in the Western Indian Ocean
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 Arabian Sea
Arabian Sea
The Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by the Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui in northeastern Somalia and Kanyakumari in India...
. P. lineatus occurs in the eastern Mediterranean, marine waters in the Indian Ocean and Western Pacific, and sometimes entering freshwaters in East Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and Madagascar. P. nkunga is distributed in southern Africa from Boknes to Boteler Point, and possibly to 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...
, in marine waters but also entering freshwater. P. papuensis ranges in the south of the island of New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
.
Description
P. canius reaches the largest size, up to 150 centimetres (59 in) TLFish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
. P. limbatus grows to 41 cm (16 in) SL
Fish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
. P. lineatus grows to 32 cm (13 in) TL. P. nkunga grows to about 51 cm (20 in) SL. P. papuensis is recorded to reach 55 cm (22 in) TL, though it may reach 100 cm (40 in) TL according to local fishermen.
All species have been confirmed to be venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous except for P. fisadoha. The anterior spines of the dorsal
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...
and pectoral fins can inflict painful wounds. In P. lineatus, the highly venomous serrate spine of the first dorsal and each of the pectoral fins may even be fatal.
The scaleless skin of P. nkunga is coated in mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
, and its mouth is surrounded by four pairs of sensory barbels
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
. The spines of the serrated 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...
, which can lock into an erect position, are covered in toxic mucus that can poison humans.
Ecology
P. canius is found mostly in estuaries and lagoons, and sometimes up rivers in nearly fresh waters. It occurs in the lower parts of rivers in freshwater or brackish water and in coastal seas. P. limbatus occurs in estuaries and along open coasts. P. lineatus is the only catfish found in coral reefCoral 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; it is also found in estuaries, tide pools and open coasts. P. papuensis is found in turbid rivers and swampy lagoons and backwaters.
Most species feed on 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, mollusks, and fishes. Adult P. lineatus search and stir the sand incessantly for crustaceans, mollusks, worms, and sometimes fish. P. nkunga feeds mainly on benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, using its barbels to feel around in the mud for crab and small fish.
P. lineatus is an oviparous
Oviparity
Oviparous animals are animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, reptiles, all birds, the monotremes, and most insects, some molluscs and arachnids....
fish; this species has demersal eggs and planktonic larvae.
Physiology
Interestingly, unlike the freshwater Siluriformes from which it evolved, Plotosus has evolved long ampullaryAmpullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
canals in its electrosensory organs (originally termed "ampullae of Lorenzini", though now the name is not used) as the voltage gradient across the skin is less than in fresh water and so they must extend deeper into the fish where the difference will be more marked in order that the maximal volatage be registered. Such deep canals are found in elasmobranchs, though not in the freshwater stingray Potamotrygon, indicating this time loss of extended canals rather than gain.