Occurrence and prevalence of infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss) cultured in cages in the Black Sea

Rainbow trout (Oncorhynchus mykiss) cultured in cage systems in the South Eastern Black Sea were surveyed for the type, occurrence and prevalence of infectious pancreatic necrosis virus (IPNV). Two nearby farms (designated as Farm A and Farm B) were visited monthly in 2007 and 2008. At each farm, 385 fish were selected randomly from five cages. Another farm with infected trout from a hatchery also was monitored for IPNV from the transfer to harvest. IPNV was found to be prevalent in both farms surveyed. In Farm A, IPNV was present throughout the growing period, from January to May, and all five randomly sampled cages tested positive for IPNV in March and April of 2007. In Farm B, IPNV was present only in February and March in 2007, and in 2008, IPNV was observed in January (two cages) and February (one cages) at low levels. Interestingly, IPNV was absent 2 weeks after transfer to the sea at 17.5°C. The same strain of IPNV, genotype III that was isolated from the same stock of fish at the hatchery, reoccurred when water temperatures dropped to 12°C in December in the Black Sea. Transferring fish to the sea at high water temperatures could lessen the negative impacts of IPNV on growth of rainbow trout in brackish water.