Major Diseases Encountered in Rainbow Trout Reared in Recircul

Recirculation systems create unique environments for fish culture. Opportunistic microorganisms may cause disease due to favorable conditions occurring in recirculation systems. The biofilters used may become reservoirs of infectious microorganisms. Stressful conditions such as suspended solids in culture tanks and high rearing densities may contribute to disease outbreaks. Additionally, noninfectious problems such as high nitrite, elevated carbon dioxide or high ozone levels may cause mortalities or produce stress. The major infectious diseases which have been encountered in trout reared in recirculation systems include: bacterial gill disease, furunculosis, amoebic infestation, Colegs sp. infestation, and the parasites Gyrodactylus, Chilodonella, Triichnoodaiina, Ichthyopthirius, and Ichtyobodo. Because eradication is particularly difficult in a water reuse culture system, to prevent introduction of infectious diseases and to reduce disease occurrence, it is important to check the fingerlings before stocking and to maintain optimum environmental conditions in the system. Disease problems are usually controllable if action is taken at the onset to stop spread of infection and steps taken to correct the stress that may have triggered the outbreak. Treatments in recirculation systems may affect biofilter function.