Influence of Water Velocity and Vertically-Suspended Structures on Rainbow Trout Rearing Performance

This study evaluated the effects of two water velocities and three types of vertically-suspended environmental enrichment during the rearing of juvenile rainbow trout (Oncorhynchus mykiss; mean ± SE, initial weight 4 ± 1 g and total length 71 ± 2 mm) in 1.8m diameter circular tanks. The 2 × 3 experimental design used two velocities (12.2 cm·s-1 and 30.5 cm·s-1) and three structural treatments (aluminum rod array, plastic spheres, or no structure). After 116 days, the fish reared without any structure (control) at 30.5 cm·s-1 had significantly lower total tank weight, gain, percent gain, feed conversion ratio, and specific growth rate compared to the other treatments. Similarly, the fish reared with a velocity of 30.5 cm·s-1 without structure were significantly shorter and lighter than those in the other treatments. There was no significant difference in condition factor and relative fin lengths among the treatments. These results indicate that vertically-suspended environmental enrichment may be impacting fish rearing performance by altering tank water velocities.