Ergasilus is a genus of copepod crustaceans occurring in both the ocean and fresh water, often called gill lice. The females are parasitic upon the gills of fishes. This is similar to members of the crustacean order Arguloida (fish lice). Being copepods, gill lice have a single median eye on their head. The second antennae are modified into prehensile pincers. Male gill lice are free-living.
Species include:
- Ergasilus anchoratus
- Ergasilus arthrosis
- Ergasilus auritus
- Ergasilus briani
- Ergasilus caeruleus
- Ergasilus celestis
- Ergasilus centrarchidarum
- Ergasilus cerastes
- Ergasilus chautauquaensis
- Ergasilus clupeidarum
- Ergasilus cotti
- Ergasilus cyanopictus
- Ergasilus cyprinaceus
- Ergasilus elongatus
- Ergasilus felichthys
- Ergasilus fryeri
- Ergasilus funduli
- Ergasilus gibbus
- Ergasilus globosus
- Ergasilus labracis
- Ergasilus lanceolatus
- Ergasilus lizae
- Ergasilus longimanus
- Ergasilus luciopercarum
- Ergasilus manicatus
- Ergasilus megaceros
- Ergasilus mugilis
- Ergasilus myctarothes
- Ergasilus nerkae
- Ergasilus orientalis
- Ergasilus rhinos
- Ergasilus sieboldi
- Ergasilus tenax
- Ergasilus turgidus
- Ergasilus versicolor
- Ergasilus wareaglei
- Ergasilus wilsoni