Effects of Partial Tank Covers on the Growth of Juvenile Feral Rainbow Trout during Hatchery Rearing

Abstract

Partial tank covers were evaluated for their effects on the growth of juvenile feral McConaughy strain rainbow trout Oncorhynchus mykiss during hatchery rearing. Trout were reared in 1999 and 2000 in circular tanks that were either completely open on top or partially (29%) covered. Trout reared in tanks with partial covers were 93 mm long at the end of 55 d of rearing in 1999, which was significantly longer than the 88-mm mean length of trout reared in uncovered tanks. Total lengths were also significantly different after 34 d of rearing in 2000: 81 mm for fish from partially covered tanks and 78 mm for fish from open tanks. The total weight gains of fish per tank were significantly greater (23.9 versus 22.7 kg) and feed conversions were significantly better (0.83 versus 0.87) in partially covered tanks in 1999. In 2000, the total weight gain of fish per tank was 15.4 kg in tanks with partial covers and 13.5 kg in uncovered tanks, and the respective feed conversions were 0.90 and 1.05. However, neither weight gain nor conversion was significantly different in 2000. No significant differences in percent mortality were observed in fish reared with or without partial covers.