SIMULATED PREDATOR RISK ON BEHAVIOR, SWIMMING ABILITY AND STRESS RESPONSE OF JUVENILE LARGE YELLOW CROAKER (LARIMICHTHYS CROCEA)

Stock enhancement has been considered to be the most direct and effective measure to restore fishery resources. However, the outcomes are unsatisfactory as expected. The main reason is that hatchery-produced fishes for restocking can not adapt wild environment well after released. The most challenge that they would face is predation risk. Many studies had shown that net-chasing treatment can simulate predator risks and pose a survival threat to fish. Appropriate intensity net-chasing training could improve the ability of juvenile fishes to deal with risk and shape the behavioral abilities to escape from predators. The large yellow croaker (Larimichthys crocea) is sensitive to external stimulation, whether the net-chasing treatment could improve the escape ability for the species remains doubt. To verify the efficiency of net-chasing to shape the abilities of the large yellow croaker, herein we performed a net-chasing training experiment with the juveniles (80 dpf). Four chasing levels, 0, 2.5min, 5.0min and 7.5min, were applied for 15d and 30d twice daily, respectively. Then, growth, behavior (novel environment test, stress coping style test, emergence test and avoidance test), swimming ability, and stress response were measured. Moreover, at a 7d interval after the 30d training, the juveniles were performed another 10min net-chasing to investigate the changes of stress response. Results showed that either in the short term (15d) or long term (30d) treatment, significance analysis shows that different intensities of chase training did not result in a significant effect on growth, however, effect size and Bayes factor indicate that effect of 30d chase training is not negligible. On the behavior, after a 15d chase training, both significance analysis and effect size indicate that the chase training affected negatively on the exploration tendency of juvenile large yellow croaker. After a 30d chase training, significance analysis and effect size indicate that the exploration tendency of 30d stronger than 15d. On the stress response, significance analysis as well as effect size indicated that the cortisol level in juvenile large yellow croaker increased significantly after a chase training for 15d or 30d. On the swimming ability, significance analysis indicated that only U_crit^a was reduced significantly after a 15d chasing training, and effect sizes indicated that both U_crit^a and U_crit^r were negatively affected highly after a 15d or 30d chase training. After a 7d interval post 30d training, significance analysis, effect size, and Bayes factor showed that cortisol level of the juveniles was significantly declined when they faced the net chasing again. In conclusion, the net chasing is probably an effective way to improve the ability of the hatchery-produced large yellow croaker for restocking to adapt the wild environments. The findings from the present study laid a certain foundation for training the large yellow croaker before release for stock enhancement.