Plotosus is a genus of eeltail catfishes native to the Indian Ocean, the western Pacific Ocean and New Guinea.
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.[2]
P. canius reaches the largest size, up to 150 centimetres (59 in) TL.[3] P. limbatus grows to 41 cm (16 in) SL.[4] P. lineatus grows to 32 cm (13 in) TL.[5] P. nkunga grows to about 51 cm (20 in) SL.[6] P. papuensis is recorded to reach 55 cm (22 in) TL, though it may reach 100 cm (40 in) TL according to local fishermen.[7]
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.[3][4][5][6][7][8]
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.[9]
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.[3] P. limbatus occurs in estuaries and along open coasts.[4] P. lineatus is the only catfish found in coral reefs; it is also found in estuaries, tide pools and open coasts.[5] P. papuensis is found in turbid rivers and swampy lagoons and backwaters.[7]