Scottish Marine and Freshwater Science Volume 4 Number 3: Epidemiology and Control of an Outbreak of Viral Haemorrhagic Septicaemia in Wrasse Around Shetland Commencing 2012

1 Introduction

Wrasse are a diverse family (Labridae) of marine fish comprising multiple genera occurring in tropical, subtropical and temperate seas ^[1] . Wrasse are increasingly used as a biological control of the salmon sealouse ( Lepeophtheirus salmonis) and salmon louse (Caligus elongatus) on Atlantic salmon ( Salmo salar) marine production sites (farms) and may be wild-caught or hatchery-reared ^[2] .

Wrasse are known to be potentially susceptible to several bacterial, viral and parasitic pathogens ^[3] although there is no previous report of susceptibility to Viral hemorrhagic septicemia virus ^[4] ( VHSV). This pathogen, a negative sense single-stranded RNA virus assigned to the taxonomic family Rhabdoviridae and genus Novirhabdovirus ^[5] , is known to infect a wide variety of marine and freshwater fish species and has the potential to cause clinical disease in at least some species of salmonid ^[6] . Infections of VHSV are listed as a non-exotic disease under European Community ( EC) Council Directive 2006/88/ EC ^[7] and in Scotland are notifiable to the competent authority under the Aquatic Animal Health (Scotland) Regulations (2009) ^[8] . Four major groups (genotypes) of VHSV named I to IV ^[9] are recognised by the World Organisation for Animal Health ( OIE) ^[10] .

This report describes the occurrence and control of an outbreak of VHS in Scotland commencing during 2012 in wild-caught wrasse used for the control of sea-lice on Atlantic salmon farms.