National Survey of the Sea Lice (Lepeophtheirus salmonis Krøyer and Caligus elongates Nordmann) on Fish Farms in Ireland - 2002

Abstract

Salmonids farmed in Ireland in 2002 can be divided into the following groups: one year class of rainbow trout Oncorhynchus mykiss and three year classes of Atlantic salmon Salmo safar. The year classes of salmon include, smolts (2002 generation), one sea-winter salmon (2001 generation) and two sea-winter salmon (2000 generation). S1/2' s are fish which are transferred to sea in Autumn/Winter of the same year that they are hatched. Their S1 siblings smoltify and are put to sea in early spring, some three to four months later. Salmon which are at sea for a year or longer in April are known as growers/one sea-winter and are treated separately from younger salmon (smolts) and rainbow trout. Those salmon that were put to sea in winter 200 I /spring 2002 are referred to as smolts, or 2002 year class fish. During the 2002 sampling period all four groups of farmed fish were examined. Two species of sea lice are found on cultured salmonids in Ireland, Caligus elongates Nordmann, a species of parasite that infests over eighty different types of marine fish, and Lepeophtheirus salmonis Krøyer, which infests only salmon and other salmonids. Sea lice are regarded as having the most commercially damaging effect on cultured salmon in the world with major economic losses to the fish farming community resulting per annum (Bristow and Berland, 1991; Jackson and Costello, 1991). They affect salmon in a variety of ways: mainIy by reducing fish growth, loss of scales which leaves the fish open to secondary infections (Wootten et aI., 1982) and damaging of fish which reduces marketability.