Effects of physical enrichment on survival, growth, and physiology of captive-reared juvenile Lake Sturgeon

ABSTRACT Objective We investigated whether physical enrichment can be used at the captive-rearing stage to promote a more natural phenotype and better prepare juvenile Lake Sturgeon for the variability of the natural environment upon release. Methods We exposed age-0 Lake Sturgeon to different types of physical enrichment for 6 months. We used four treatments: a nonenriched (control) tank, a tank with gravel substrate, a tank with vertical structures, and a tank with both gravel substrate and vertical structures. We tracked the survivorship, growth, and body condition of each fish throughout the experiment and analyzed their dorsal color pattern prior to and following 5 months of enrichment exposure. At the end of the experiment (6 months), we measured several physiological parameters, including metabolic rate, plasma cortisol, and critical thermal maximum. Results We observed mortalities in all the enriched tanks but not in the nonenriched tank. Growth rate and body condition varied considerably between enrichment treatments across time. The fish that were reared with structures alone displayed a lower routine metabolic rate and higher aerobic scope than those in all the other treatment groups. We did not observe any effects of enrichment on the critical thermal maximum or the baseline or stress-induced cortisol levels in these fish. Conclusions We recommend that hatchery managers add structures that allow for sheltering and resting behaviors to the rearing environment of age-0 Lake Sturgeon for a few months prior to release. Our study highlights the value of physical enrichment for improving the welfare of captive-reared fish, which could translate to higher rates of postrelease survival and success for reintroduced age-0 Lake Sturgeon.