Abstract

A field survey was carried out to determine the occurrence and spread of viral haemorrhagic septicaemia virus (VHSV) in whiting Merlangius merlangus (L.), a key prey species in the southeastern Black Sea region. In March, April, September and December 2007 and monthly in 2008, 70 to 105 M. merlangus captured by gill nets were examined in pools of 7 fish per pool (total number of fish = 1603). After determining the seasonal occurrence of VHSV in whiting, 43, 80 and 88 whiting were sampled individually in January, February and March 2009, respectively, to determine age and size of whiting commonly infected with VHSV. The samples were tested in duplicate using BF-2 and EPC cell lines for virus isolation. Positive cultures (those demonstrating cytopathic effect, [CPE]), were tested further with a commercial ELISA kit to confirm that the observed CPE was caused by VHSV. VHSV was detected in M. merlangus only between February and April following a drop in the surface water temperature to 9 degree C. All infected fish from the sampled whiting were asymptomatic carriers with low levels of virus. The estimated prevalence from pooled samples ranged between 1.35% (2.5 to 97.5 percentiles; 0.04 to 7.32%) to 3.14% (0.36 to 10.95%), whereas prevalence estimated from individual sampling was 7, 5 and 1% in January, February and March, respectively. Individual sampling also revealed that prevalence was higher among young fish (1 to 1.5 yr old) and decreased with increasing age. This is the first report of VHSV infection in whiting in the Black Sea.