Halibut behaviour as a means of assessing suitability of ongrowth systems

Abstract

Halibut behaviour in net pens has been studied using direct observation, underwater video and/or hydroacoustic equipment. Rearing experience includes a wide range of fish weights (50-10.000 g) and fish densities (4-150 kg/m2). Individual halibut is able to change their coloration on the ocular side from their whitespotted benthic camouflage to the uniformly brown-grey pelagic camouflage within a minute and vice-a-versa. The proportion of fish with pelagic camouflage on/near the bottom was high in the net pens with high densities, and such groups also showed suboptimal growth. The results also indicated an increase in pelagic swimming activity in the net pens with the highest densities. High light levels and low temperatures decreased the pelagic swimming activity of the fish. Halibut in net pens reared at low densities did not spread evenly on the bottom, but were usually found in clumps.