Effects of physical enrichment and predator stress on growth, behavior and respiratory metabolism of juvenile marbled rockfish (Sebastiscus marmoratus)

Stock enhancement based on hatchery-reared fish has become one of the most common forms of management practices in marine fisheries resource restoration. However, a lack of environmental stimulation contributes to the poor survival adaptability of hatchery-reared fish in the wild, with negative consequences for post-release performance in natural environments. To investigate whether incorporating physical enrichment and predator stress into aquaculture environments can enhance the survival adaptability of hatchery-reared fish, this study conducted a two-factor interaction experiment to examine the effects of predator stress and physical enrichment on the growth, behavior, and respiratory metabolism of juvenile marbled rockfish (Sebastiscus marmoratus).The findings are as follows: ① Physical enrichment significantly improved the final body weight of the juveniles (P<0.05), demonstrating its positive effect on growth in controlled environments. On the other hand, prolonged predator stress inhibited fish growth, leading to decreased final body weight, weight gain rate, and specific growth rate, highlighting the potential trade-offs of predator stress on growth. ② Predator stress did not have a significant impact on the activity or boldness of juvenile marbled rockfish but did significantly reduce their exploratory behavior, suggesting a specific behavioral adjustment under stressful conditions. ③ In the presence of predators, physical enrichment could increase juvenile fish’s activity, indicating its role in promoting active behaviors even in predator-present environments. ④ Physical enrichment did not significantly impact predator avoidance behavior responses, but long-term coexistence with predators significantly reduced the cumulative duration spent in risky areas by the juvenile fish. This reflects the potential of predator stress to shape risk-avoidance strategies over time. ⑤ Physical enrichment markedly reduced the oxygen consumption rate of juvenile fish (P<0.01), suggesting a reduction in metabolic stress or enhanced energy efficiency. In contrast, predator stress significantly increased oxygen consumption (P<0.05), reflecting heightened metabolic demands associated with stress responses. ⑥ Both physical enrichment and predator stress had significant interaction effects on the exploratory behavior, activity levels, and respiratory metabolism of the juveniles. These interactions provide critical insights into the mechanisms through which environmental enrichment influences fish growth and behavioral adaptability. Based on these findings, this study recommends incorporating physical enrichment and controlled predator stress exposure as part of the pre-release acclimation process for hatchery-reared marbled rockfish. Such practices could effectively improve the environmental adaptability of hatchery-reared marbled rockfish, thereby potentially enhancing their survival performance after releasing into the wild.