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

Abstract

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 1.8-m 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.

Use of Exercise and Structure during Rainbow Trout Rearing

“…Despite the relatively high loading densities, the feed conversion ratios observed in this experiment are similar to those previously reported for rainbow trout [25] [45]. At 2.3 to 2.6, the specific growth rates, which is basically the percentage growth per day of fish, in this study were also similar to those reported by Huysman et al [32] and Voorhees et al [45]. Condition factors were also similar to those reported previously for rainbow trout [25]…”

“…However, at higher velocity levels that produced vigorous exercise, positive effects on fish rearing performance were not observed. This is similar to the results of other studies using high velocities for exercise or not allowing for any rest periods [25] [44] [45], which all likely produced exercise fatigue [42] [34]. It must be noted however, that the results from using structure in this study differ from those of White et al [28], Huysman et al [31], and Jones et al [33].…”

“…Mean (± SE) final tank weight, gain, food fed, feed conversion ratio (FCR a ), and percent mortality of rainbow trout reared with or without vertically-suspended strcture and with or without an exercise routine (n = 4 structure and exercise. However, Voorhees et al [45] did report a significant interaction. Vertically-suspended rods and vertically-suspended plastic spheres were used for 119 days at two continuous velocities (approximately 1.7 BL•s −1 and 4.0 BL•s −1 ) and found significantly poorer rearing performance in exercised trout reared without structure.…”

“…Vertically-suspended rods and vertically-suspended plastic spheres were used for 119 days at two continuous velocities (approximately 1.7 BL•s −1 and 4.0 BL•s −1 ) and found significantly poorer rearing performance in exercised trout reared without structure. It is likely however, that the continuous exercise regime used by Voorhees et al [45] led to the significant interaction between velocity and exercise by causing exercise fatigue [42] [43] [44] [45], unlike the intermittent exercise protocol used in this study. The positive effects of the exercise routine used in this study on trout growth and feeding efficiency are not surprising.…”

“…Exercise is generally regarded as beneficial by improving swimming stamina, increasing hatchery growth, and positively impacting fish behavior [35]- [41]. Continual exercise for long durations may lead to exercise fatigue however [42] [43] [44] [45]. Routines that balance exercise with rest periods are likely more beneficial [46]- [51].…”