Plotosus Nkunga

''Plotosus'' is a genus of eeltail catfishes native to the Indian Ocean, the western Pacific Ocean and New Guinea.

Species

There are currently nine recognized species in this genus:
* '' Plotosus abbreviatus'' Boulenger, 1895
* '' Plotosus canius'' Hamilton, 1822 (Gray eel-catfish)
* '' Plotosus fisadoha'' Ng & Sparks, 2002
* '' Plotosus japonicus'' Yoshino & Kishimoto, 2008 (Japanese Striped eel-catfish)( ゴンズイ)
* '' Plotosus limbatus'' Valenciennes, 1840 (Darkfin eel-catfish)
* ''Plotosus lineatus'' ( Thunberg, 1787) (Striped eel-catfish)
* '' Plotosus nhatrangensis'' Prokofiev, 2008
* '' Plotosus nkunga'' Gomon & Taylor, 1982 (Stinging eel-catfish)
* '' Plotosus papuensis'' Weber, 1910 (Papuan eel-catfish)

Distribution

''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.

Description

''P. canius'' reaches the largest size, up to 150 centimetres (59 in) TL. ''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 venomous 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 be poisonous to 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 reefs; 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 crustaceans, 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 invertebrates, 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.

Physiology

Unlike the freshwater ''Siluriformes'' from which it evolved, ''Plotosus'' has evolved long ampullary 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 voltage 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.

References

{{Taxonbar, from=Q1082699

Plotosidae
Fish of Africa
Fish of Asia
Endemic fauna of Madagascar
Fish of New Guinea
Venomous fish
Catfish genera
Taxa named by Bernard Germain de Lacépède
Marine fish genera