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Use of Exercise and Structure during Rainbow Trout Rearing

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.