Ergasilidae is a widespread family of copepods and comprises many species. The type genus is Ergasilus. With a few doubtful exceptions all ergasilids are parasitic on fishes.
Biology Various species of Ergasilidae parasitise hosts in various habitats, mostly freshwater, but some attack marine species, especially euryhaline fishes such as mullet. Because the best-known species are adapted to attack the gill filaments of the fishes, Ergasilidae are known by common names such as gill lice. However, some species have been found infesting, and presumably causing, external skin lesions of fish.
Immature instars and mature males of Ergasilidae are fairly typical free-living planktonic copepods. The mature females also can swim competently and at least one species, Ergasilus chautauquaensis, is not known to be parasitic at all. However, that is exceptional; most adult females are parasitic and have morphological adaptations for attacking the gills of host species of fishes.
Though their antennules retain their sensory function, the main second antennae of the adult females are adapted to clinging to the gill filaments of host fishes. In many Ergasilus species it is not clear that mature females are able to release their grip once attached, but when forcibly detached from the host's gills they swim without difficulty.
Another adaptation in parasitic females is that their first legs are armed with heavy, blade-like spines, and in some species the joints also are fused, stiffening them and increasing their effectiveness for harvesting host tissue. Once attached to the gills, the females use their first pair of legs to rasp off gill mucus and tissue and move it forward towards the mouth.
In the genus Ergasilus only the adult females are parasitic. The planktonic males do not venture inside fishes, so fertilisation must take place before the females attach themselves to the host's gills.
Economic significance Since the Ergasilus females attack the gills of fish, a heavy infestation can cause severe damage and secondary infections, interfere with respiration, and sometimes kill the host. In some fisheries and aquacultural enterprises the mortality and morbidity among fish stocks can present serious economic and ecological problems.
Genera The family Ergasilidae contains the following genera:
Abergasilus Hewitt, 1978 Acusicola Cressey, 1970 Amplexibranchius Thatcher & Paredes, 1985 Anklobrachius Thatcher, 1999 Brasergasilus Thatcher & Boeger, 1983 Dermoergasilus Ho & Do, 1982 Ergasilus von Nordmann, 1832 Gamidactylus Thatcher & Boeger, 1984 Gamispatulus Thatcher & Boeger, 1984 Gamispinus Thatcher & Boeger, 1984 Gauchergasilus Montu & Boxshall, 2002 Majalincola Tang & Kalman, 2008 Miracetyma Malta, 1993 Mugilicola Tripathi, 1960 Neoergasilus Yin, 1956 Nipergasilus Yamaguti, 1939 Paeonodes C. B. Wilson, 1944 Paraergasilus Markevich, 1937 Pindapixara Malta, 1994 Prehendorastrus Boeger & Thatcher, 1990 Pseudovaigamus Amado, Ho & Rocha, 1995 Rhinergasilus Boeger & Thatcher, 1988 Sinergasilus Yin, 1949 Teredophilus Rancurel, 1954 Therodamas Krøyer, 1863 Thersitina Norman, 1905 Vaigamus Thatcher & Robertson, 1984
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