To Reduce Mortality of Fry Fish ( Oncorhynchus mykiss ) Caused with Viral Infection (IPNV and VHSV) by Water Treatment with Chloramin-T as Disinfectant

Abstract

In winter of 2015 we observed gross mortality of fry fish in some tanks of a hatchery in Iran. They had dissonant swimming, spiral swimming, skin darkness, abdominal distension, and anorexia. At the beginning, mortality was low but it increased more and more during the several days. The fry were in fiberglass tanks with 1000 litres of water. It was about 20000 fry in each tank at the beginning. Two activities did synchronously while mortality observation. At the first, some fry sampled from each tanks and sent to laboratory for pathogen detection. The next, 9 tanks selected and grouped as 3 treatments (control, treatment-1 and treatment-2). Control treatment was consisting of 3 tanks that they had not mortality. Treatment-1 and Treatment-2 have the highest mortality and each of them was consisting of 3 tanks. Then, 10 ppm chloramin-T as disinfectant compound added to each tanks of treatment-1 during 1 hour in 3 continuous days (3 times). The tanks of treatment-2 added no drug. After 7 days mortality of fry in each tank estimated and compared with each other. Survival in tanks of treatment-1 was about 76% while survival in tanks of treatment-2 was about 27% while survival in control tanks was about 98%. One month later, results of laboratory tests reported. We found that fish of control tanks were safe (without pathogen) while fish of treatment-1 and treatment-2 were infected with IPN-virus and VHS-virus based on RT-PCR test. Totally 36 fry had been examined by RT-PCR. We founded that 10 fry were IPN+ and 2 of them were VHS+. Clearly; results showed that chloramin-T is able to control the viral infection of Oncorhynchus mykiss (p<0.05) in statistical comparison, it confirmed with SPSS software by using Anova-test. Chloramine-T increased surveillance from 27% to 76% while viral contamination had been confirmed.