As with anchor worms, fish lice make little holes in the fish, making them vulnerable to bacterial infections. Symptoms include loss of appetite, listlessness, flashing, and excess slime production. Like costia, chilodonella are microscopic. Symptoms are similar to those caused by costia. Flukes are the most commonly found parasite on koi and goldfish.
High numbers can cause serious damage.
Symptoms include flashing, gasping at the surface, frayed fins, and death. Most cases of ulcer disease are preceded by fluke infestations. Another microscopic parasite, trichodina is easily identifiable. It resembles a wagon wheel. Fish infected with trichodina often develop a gray film over the body in response to the infestation.