Thermal behaviour of rainbow trout and Arctic char in cages moored in stratified water

Using implanted acoustical tags, the body temperature and external water temperature of rainbow trout and Arctic char were monitored in commercial fish pens moored in an environment which was extremely stratified with respect to temperature and salinity. Both species regulated body temperature between 13 and 14-degrees-C, and none of the fish made excursions into deeper, cooler salt water. Char avoided warmer surface water. Several trout exhibited diurnal cycles in preferred temperature that fluctuated 3-4-degrees-C.