Use of Exercise and Structure during Rainbow Trout Rearing

Abstract

A combination of two forms of environmental enrichment (in-tank structure and exercise) was evaluated during the hatchery rearing of juvenile rainbow trout Oncorhynchus mykiss. The study used four treatments: 1) neither exercise nor structure, 2) exercise without structure, 3) structure without exercise, and 4) both exercise and structure. Velocities in the unexercised tanks were a constant 12.2 cm•s −1. Velocities in the exercised tanks alternated weekly with one week at 12.2 cm•s −1 followed by a week at 30.5 cm•s −1. Structural enrichment consisted of an array of vertically-suspended aluminum angles. The use of either environmental enrichment technique significantly improved final tank weight, gain, percent gain, and specific growth rate. Feed conversion ratio was significantly and positively influenced only by structure, but fish on the exercise routine were overfed. There were no significant interactions between exercise and structure, indicating that each form of environmental enrichment operates independently. The results of this study indicate fish rearing performance can be improved with the addition of either vertically-suspended aluminum angles or an exercise routine, but the combination of the two techniques may not be needed to improve rainbow trout growth.

Effects of Intermittent Exercise during Initial Rainbow Trout Oncorhynchus mykiss Rearing in Tanks Containing Vertically-Suspended Environmental Enrichment

“…The feed conversion ratios obtained in this study are consistent with the observations of Huysman et al [29] and Voorhees et al [16]. They are also similar to studies using similarly sized rainbow trout in environmental enrichment studies [15,25,27].…”

“…The lack of difference in growth between the control and exercise regime tanks in this study support the observations of Voorhees et al [16] that a combination of both physical and occupational enrichment was not necessary to improve the hatchery rearing performance of rainbow trout. Voorhees et al [16] reported that either exercise or vertically-suspended structures increased trout growth, but that no further improvements were realized when both forms of environmental enrichment were combined. The lack of any improvement in growth observed using exercise in this study was likely due to the presence of vertically-suspended structures in both the exercise and non-exercise tanks.…”

“…The specific growth rates of this study are consistent with those of similarly-sized rainbow trout reared using vertically-suspended enrichment [15,16,29]. However, Gregory and Wood [7] reported a much lower specific growth rate for juvenile rainbow trout of similar size who were exercised intermittently than was observed in this experiment.…”

“…For example, Parker and Barnes [37] found positive effects of exercise in a trial using 72 mm long rainbow trout. Voorhees et al [16] conducted an exercise study with 69 mm rainbow trout and Reiser et al [11] used rainbow trout that were 409 mm long. Exercise studies using other salmonid species have also used larger fish, such as the 130 mm Arctic charr (Salvelinus alpinus) used by Christiansen and Jobling [12].…”

Color of Vertically-Suspended Structure Does Not Impact the Growth of Rainbow Trout Reared in Circular Tanks

“…It is possible that this study lasted too long in relation to fish rearing densities. Voorhees et al [24] and Huysman et al [25] suggested that high rearing densities, such as those observed at the end of this study, may lead to density-dependent reduced growth rates. By allowing fish in the slower-growing treatments the time to catch up in size to those fish in faster-growing treatments that reach higher densities more quickly, longer study durations may preclude the determination of significant differences among treatments.…”