Partial Overhead Tank Cover Use during Feral Brown Trout Rearing

Abstract

AbstractOverhead cover is an essential component of the habitat of wild brown trout Salmo trutta but is typically lacking during hatchery rearing. To evaluate the effect of cover during hatchery rearing, we grew feral brown trout in circular tanks that were either completely open on top or partially (29%) covered. After 51 d of rearing in 2001, the total biomass of fish per tank was significantly greater in the partially covered tanks than in the completely open tanks. Feed conversion was also significantly reduced by the use of partial tank covers (1.13 versus 1.29 in the open tanks). After 45 d of rearing in 2003, the mean total weight gain of fish per tank was 13.8 kg in tanks with partial covers and 12.9 kg in uncovered tanks, and feed conversion was 0.79 for partially covered tanks and 0.85 for uncovered tanks. In addition, fish reared in tanks with partial covers were significantly longer and heavier (56.3 mm, 1.62 g) than fish reared in open tanks (54.1 mm, 1.42 g), although there was no significant difference between the open or partially covered tanks in total tank weight gain or conversion in 2003. No significant differences in percent mortality were observed between groups reared in partially covered and uncovered tanks. The use of partial tank covers can increase the growth of feral juvenile brown trout in circular tanks during hatchery rearing.