Structural Complexity Improves the Rearing Performance of Rainbow Trout in Circular Tanks

Abstract

AbstractWhile structural complexity has been used extensively during hatchery rearing in an attempt to improve poststocking survival, the potential impact of this complexity on hatchery rearing performance has largely been ignored. This study examined the growth and condition of juvenile Rainbow Trout Oncorhynchus mykiss reared in nearly fully covered circular tanks containing nine vertically oriented round aluminum rods (structurally complex) compared with that of trout reared in almost fully covered tanks with no rods (control) at two water velocities (2.0 body length (BL)/s and 2.75 BL/s). After 51 days, total tank weight gain was significantly higher in the structurally complex tanks than in the control tanks, regardless of water velocity. The feed conversion ratio was also significantly better in the structurally complex tanks [mean (SD) 1.25 (0.10)] than in the control tanks [1.66 (0.41)]. There were no significant differences in hepatosomatic index, splenosomatic index, and viscerosomatic index between the fish from the structurally complex and the control tanks. Total tank weight gain was significantly higher and the feed conversion ratio significantly lower in the lower water velocity tanks than in the higher water velocity tanks. These results indicate that vertically oriented aluminum rods can be used to increase structural complexity and improve Rainbow Trout rearing performance in circular rearing tanks, with minimal effects on regular tank cleaning.