USE OF CLEANER-WRASSE (CENTROLABRUS-EXOLETUS (L) AND CTENOLABRUS-RUPESTRIS (L)) TO CONTROL INFESTATIONS OF CALIGUS-ELONGATUS NORDMANN ON FARMED ATLANTIC SALMON

Trials were conducted in experimental tanks and in commercial scale se a cages to evaluate the ability of wrasse to control sea lice infestat ions on farmed Atlantic salmon smelts. In a 3 h tank trial rockcook wr asse, Centrolabrus exoletus (L,), removed an average of 19 lice per fi sh h(-1) from salmon smelts infested mainly by Caligus elongatus Nordm ann (93%) and with lower numbers of Lepeophtheirus salmonis (Kroyer) ( 7%). Goldsinny wrasse, Ctenolabrus rupestris (L.), did not remove lice from salmon over this 3 h period. Chalimus stages I and II were remov ed at a lower rate than were older and larger life history stages. Bot h species of wrasse failed to prevent rapid increases in infestations of C. elongatus in commercial cages in 1992 and 1993 at initial wrasse to salmon ratios ranging from 1:37 to 1:146. However, SCUBA diving ob servations confirmed that both wrasse species did remove C. elongatus from salmon in these cages. In the 10 m deep cages, wrasse occurred ma inly at depths greater than 6 m while salmon occurred primarily betwee n 2 and 5 m. Goldsinny had a significantly shallower distribution than rockcook. Both species associated closely with the cage net and with objects in the cage and interactions with salmon appeared to be relati vely uncommon. Rigorously controlled trials on commercial farms need t o be carried out in order to define protocol for the use of wrasse und er these conditions.