PREY SELECTION AND DAILY FOOD-CONSUMPTION BY A CLEANER FISH, CTENOLABRUS-RUPESTRIS (L), ON FARMED ATLANTIC SALMON, SALMO-SALAR L

Feeding electivity and daily food consumption by a cleaner fish goldsi nny wrasse, Ctenolabrus rupestris (L.) on sea lice, Lepeophtheirus sal monis Kroyer, on farmed Alantic salmon, Salmo salar L., was assessed b y comparison of lice numbers and developmental stages on salmon in pen s with and without wrasse. Mobile stages of L. salmonis in the pen wit h wrasse remained low (1-8 per fish) with no requirement for chemical treatment compared with a heavy infestation (up to 50) on the control pen. Wrasse selectively preyed on the larger lice stages, mainly adult s and female pre-adult Stage II, and this was measured and statistical ly tested using Pearre's selection index. The mean number of mobile L. salmonis consumed daily by an individual wrasse varied from 26-46 at water temperatures of 10(-12)-degrees-C and daily food consumption was 1. 18-2.72% of body weight.