Quantitative comparison of peritoneal washes and feces for detecting infectious pancreatic necrosis (IPN) virus in carrier brook trout

Paired fecal samples and peritoneal washes were taken from 300 18-month-old brook trout for determining their relative value in detecting IPN virus. The testing of feces revealed 14 times as many carriers as were found by peritoneal washes. Initial examinations showed at least 63% of the fish to be carriers of the virus, but 30% more were detected in four additional tests. Fecal output of virus from 37 fish was quantified up to five times during a period of 7 months which included the spawning season. Although there were exceptions, fish with high outputs of virus tended to maintain that level, and low titer carriers tended to yield small amounts, and in some instances, no virus. Tests of fecal extracts which were pooled from 5, 10, and 15 fish showed that virus was readily detected in all three. For economy and efficiency, the use of 10- or 15-sample pools is recommended for determining the presence of IPN in fish.