AFM 317 FISH HEALTH MANAGEMENT

Protozoa Most of the commonly encountered fish parasites are protozoan. With practice, these can be among the easiest to identify, and are usually among the easiest to control. Protozoan is single-celled organisms, many of which are free-living in the aquatic environment. Typically, no intermediate host is required for the parasite to reproduce (direct life cycle). Consequently, they can build up to very high numbers when fish are crowded causing weight loss, debilitation, and mortality. Five groups of protozoan are described below: ciliates, flagellates, myxozoans, microsporidians, and coccidians. Parasitic protozoan in the latter three groups can be difficult or impossible to control as discussed below. 3.1 Ciliates Most of the protozoan identified by aquarists will be ciliates. These organisms have tiny hair-like structures called cilia that are used for locomotion and/or feeding. Ciliates have a direct life cycle and many are common inhabitants of pond-reared fish. Most species do not seem to bother host fish until numbers become excessive. In aquaria, tanks and ponds which are usually closed systems, ciliates should be eliminated. Uncontrollable or recurrent infestations with ciliated protozoan are indicative of a husbandry problem. Many of the parasites proliferate in organic debris accumulated in the bottom of a tank or vat. Ciliates are easily transmitted from tank to tank by nets, hoses, or caretakers' wet hands. Symptoms typical of ciliates include skin and gill irritation displayed by flashing, rubbing, and rapid breathing.