while they feed on suspended bacteria. Some species are certainly primary pathogens, however, since they occur in sterile sites (e.g. urinary system), or provoke pronounced responses on the part of the host (e.g. Tripartiella on gills). When trichodinids become a problem in aquaculture, it usually indicates eutrophication or poor water quality. High bacterial loads provide abundant food for trichodininds, which subsequently proliferate on hosts and then cause attachment-related pathologies. References Oligohymenophorea Ciliate genera Parasitic alveolates Parasites of fish