Efficacy of a Modified Health Assessment Utilized on Two Genetically Distinct Stocks of Rainbow Trout

The Rainbow Trout Oncorhynchus mykiss is a salmonid fish that is maintained in aquaculture facilities and used as a source of protein around the world. Veterinarians need accurate, efficient tools and straightforward assessments to evaluate the health status of fish, like Rainbow Trout, that are cultivated on farms. In this study, two genetically distinct broodstock lines of Rainbow Trout originally obtained from two different U.S. states but propagated at Rushing Waters Trout Farm (Palmyra, Wisconsin) were evaluated. Groups originating from both states (State A: n = 20; State B: n = 20) were surveyed with a modified health assessment in a prospective, randomized, single-blind study. The adapted health assessment included external and internal gross evaluations, skin scrapes, gill clips, intestinal scrapes, and calculated indices, including condition factor and the hepatosomatic index. Generally, there were few significant differences in health assessment values between State A and State B fish. When this information was presented to the producer, it was discovered that perceived differences between groups were due to management errors in calculated growth rates. The results of this study add validity to the use of standardized health assessments for evaluating fish within aquaculture.