From Fish
Isopod adult on gills

Isopods (sea lice) are crustaceans that are widely distributed throughout the world in marine and estuarine environments, with a few species found in fresh water.

These parasites adhere to fish gills, skin, and fins and may also live in the mouth and gill cavities. Isopod infestation is confirmed by gross observation. The presence of this parasite can interfere with feeding, cause chronic stress, and result in growth retardation and make the fish susceptible to bacterial and/or parasitic invasions.

Injured tissues are frequently invaded by secondary bacterial pathogens, and this may lead to disease or even death of the fish.