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 goldsinny wrasse, Ctenolabrus rupestris (L.) on sea lice, Lepeophtheirus salmonis Kroyer, on farmed Alantic salmon, Salmo salar L., was assessed by comparison of lice numbers and developmental stages on salmon in pens with and without wrasse. Mobile stages of L. salmonis in the pen with 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 adults and female pre-adult Stage II, and this was measured and statistically 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.