There are currently nine recognized species in this genus:[1] P. canius originates from coastal regions of Thailand, Sundaland, Sulawesi, Moluccas, and India, and into the lower Mekong River.

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 to Zanzibar, in marine waters but also entering freshwater.

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.

[5] 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.