The behavioral and physiological responses of juvenile large yellow croaker (Larimichthys crocea) to different types of predator stimuli

Predator recognition is crucial for the survival of fish, enabling effective anti-predator responses and avoids survival disadvantages caused by inappropriate reactions. Thus, incorporating predator recognition training into stock enhancement programs can enhance post-release survival rates of juvenile fish by reinforcing these innate survival mechanisms. While chemical cues are often emphasized in fish anti-predator studies, the roles of visual cues and multimodal sensory integration remain understudied in marine fish. To clarify the recognition mechanism of predator signals by juvenile large yellow croaker (Larimichthys crocea), this study systematically compared the effects of stimulus type (visual, chemical, coupled) and stimulus level (low, medium, high) on anti-predator behavior and plasma cortisol levels. The behavioral analysis results showed that the main effect of stimulus type was significant (p < 0.001), and visual cues mainly triggered immediate anti-predator behavior. The induced freezing time was significantly higher than that of other stimuli (p < 0.05), and the freezing time and the vertical movement time decreased significantly with the increase in visual cue (p < 0.05). The physiological results indicated that there was an interaction effect between stimulus type and stimulus level in cortisol levels (p < 0.001). Under the low-level of coupled cues, cortisol levels were significantly higher (34.57 ± 0.71 ng/mL, p < 0.001) than those under single-modal cue (visual: 21.12 ± 4.37 ng/mL, p < 0.01; chemical: 23.73 ± 1.84 ng/mL, p < 0.05), demonstrating that low-level coupled cues can synergistically enhance physiological stress responses. These findings highlight the important role of visual cues in predator recognition in the multi-sensory integration mode of juvenile L. crocea. These results provide a theoretical basis for sensory training of proliferated and released species, especially by incorporating coupled cue training into proliferation plans aimed at increasing population numbers. By synergistically enhancing the young fish's perception of predation risks, it has application value for optimizing breeding practices and improving the survival rate of released fish.