Parasitic Leeches and Copepods on Fish
Although not a common problem, occasionally, fish will be observed infected with either leeches or copepods. Leeches have long, slender flexible bodies and actively swim for an attack on their prey. Skin and underlying soft tissues are damaged and allow blood to flow into the leech’s digestive tract. Leeches are not host-specific, and the damage to the skin and gills is dependent upon the number of leeches present at any time. Small fishes can be seriously injured or die due to excessive leech infestation.
Copepods include fish lice or “anchor worms”. The more common fish lice include Lepeophtheirus and Caligus, and Argulus. The most common genus of anchor worms includes Lernae sp. All of these are external parasites which affect the fish by imbibing blood from the host fish and causing localized skin and soft tissue damage. They may also allow for secondary bacterial infection of the skin or musculature which may ultimately cause the demise of the fish.