Fish & Intestinal Parasites

Intestinal parasites infect both fresh and salt water fish. Parasites depend on the fish as a source of food during all or part of its life cycle. The parasites benefit from the interaction, but the fish do not. Usually harm comes to the fish on which the parasite chooses to live. Intestinal parasites destroy tissues, remove blood and allow secondary infection to occur. These parasites may divert part of the fish's nutritional needs, causing malnutrition.

  1. Types

    • Six types of parasites infect fish intestines; flagellates, coccidia, nematodes and cestodes. Flagellates, mobile protozoa, invade both internally and externally. Coccidia move into the intestinal cells, while nematodes (roundworms) and cestodes (tapeworms) usually attach to the intestinal surface. Correct diagnosis is essential for proper treatment. Most intestinal parasites can be diagnosed using a microscope.

    Flagellates

    • Protozoan flagellates have tail-like projections on their bodies for mobilization. These tiny (5- to 20-micron), one-celled creatures cause thinness and abdominal distention. Additional infectious signs include; reduced appetite and clear or yellow mucus-like feces. Microscopic evaluation of dead fish intestine verifies this infection by viewing spiraling protozoa. Medicate infected fish with metronidazole in the tank at 19.9 milligrams per gallon of water, or with food at 10 milligrams per gram of food.

    Coccidia

    • Coccidia inhabit the cells of the intestinal lining. Ingested coccidia spores attach to the lining and form cysts. The spores come directly from contaminated environment or an intermediate host, such as a worm. New spores release into the intestine as coccidia mature, which further contaminates the environment. Microscopic examination of feces identifies this parasite and amprolium treatment ensues, although it's not always 100 percent effective.

    Roundworms

    • Roundworms inhabit the stomach and intestines of fish. Sometimes they migrate into the muscle or abdominal cavity. Signs of roundworm infection include anemia, wasting, and depression. Two kinds of roundworm infect fish: camillanus and capillaria. Camillanus, small thread-like worms, protrude from a fish's anus, while the larger capillaria appear in the gut. Both require treatment with fenbendazole mixed at 0.25 percent in fish food.

    Tapeworms

    • Tapeworms use a fish as a primary or intermediate host for their life cycle. Fish ingest infected snails or water fleas and the tapeworm develops to maturity inside the intestine or burrows into tissues. Mature tapeworms in tissue produce larval bumps on the fish. If a bird or human eats this uncooked fish, the larva mature in their intestines. Effective treatment includes praziquantel at 2 to 10 milligrams per liter of water for one to three hours.

    Significance

    • Fish intestinal parasites affect both aquarium owners and fishing industries. Deaths of expensive tropical fish frustrate hobbyists and fish farm sickness debilitates production. Environmental issues cause most fish health problems: poor-quality water, overcrowding, unhealthy diets or stress. Proper management of fish culture prevents parasitic overload and reduces economic loss. Contact cooperative extension agents regarding aquaculture techniques and questions.