Effects of environmental enrichment on growth performance, aggressive behavior and stress-induced changes in cortisol release and neurogenesis of black rockfish Sebastes schlegelii

Fish welfare and behavioral flexibility in aquaculture have gained increasing concern among scientists and the public. Stress-related behavioral and physiological responses and neural plasticity are important aspects of fish welfare. Recently, environmental enrichment has been regarded as a promising way to promote fish growth, decrease aggression, and enhance behavioral flexibility; however, relatively few studies focusing on the effects of enrichment and stress on fish neural plasticity have been conducted. In this work, we tested the main and interaction effects of physical enrichment (rearing for eight weeks) and/or acute stress (air exposure and confinement) on the growth performance, aggressive behavior, stress response, and brain expression levels of genes involved in neurogenesis (i.e., proliferating cell nuclear antigen, doublecortin and neuronal differentiation factor; pcna, dcx and neurod, respectively) of juvenile black rockfish Sebastes schlegelii. In general, environmental enrichment treatment significantly decreased fish aggressive behavior and the levels of basal cortisol, while it enhanced the gene expression levels of pcna and dcx in the brain. As expected, the fish exposed to acute stress had significantly higher levels of cortisol and brain pcna gene expression compared with fish at a basal status. Enrichment and stress had significant interaction effect on fish cortisol levels. Furthermore, statistically significant correlations (P < .05) between aggressive behavior and stress response (indicated by cortisol level) and between cortisol and neurogenesis biomarkers (especially pcna) were observed. The growth performance of the enriched fish was statistically similar to that of the barren-reared fish. No main or interaction effect of enrichment and stress on brain neurod gene expression was detected. This is the first evidence showing that environmental enrichment and acute stress can produce significant effects on processes of fish neurogenesis. These findings confirm the positive effects of environmental enrichment on fish stress responses and neurogenesis in the context of acute stress, which may lay the foundation for improved welfare and behavioral flexibility of fish in the aquaculture industry.