Black spot is one of the most frequently observed parasites of fish. It appears as small black spots or cysts in the skin, fins and flesh of fish. In the black spot life cycle, fish-eating birds such as herons and kingfishers eat an infected fish. The larval stage, which is inside the black cyst, develops into an adult in the bird. Eggs are laid by the adult and pass into the water where they hatch and infect snails. Eventually they leave the snail host and burrow through the skin of fish and form cysts, which the fish surrounds with a black pigment. This organism does little harm to the fish, but gives the fish an unsightly appearance. Infected fish can be consumed with proper cooking.
