Behavioral and physiological responses of juvenile black rockfish (Sebastes schlegelii) to background colors

To investigate the effects of background colors on the behavior and physiology of juvenile Sebastes schlegelii and identify suitable background colors for their growth, this study examined how five different background colors (red, blue, black, green, and white) influenced growth performance, individual behavior, and serum physiological indicators. Correlation analyses among behavioral metrics were also conducted. The results showed that the black background group’s weight gain rate (44.64%±21.09%) and specific growth rate (1.28%±0.53%) were significantly lower than those in the green (65.41%±25.64%, 1.76%±0.59%) and white (64.53±19.97, 1.75±0.44) groups (P<0.05). Fish in the black group (52.28%±11.11%) took significantly longer to explore novel objects compared to the green group (22.82%±6.87%), while the white group (46.20±26.86) exhibited significantly higher aggression frequencies than the blue (8.00±2.19) and black (8.10±3.44) groups. Additionally, the white group (12.94%±6.07%) spent a significantly higher percentage of time in bright areas than the red (0.87%±0.36%) and black (0.17%±0.10%) groups. Behavioral correlations revealed that boldness was positively associated with exploratory behavior (P<0.05) and aggression (P<0.01) but negatively correlated with anxiety levels (P<0.05). Aggression was positively linked to activity levels (P<0.05) but negatively related to anxiety (P<0.05). Physiological analyses indicated that the hematocrit (Hct) levels in the red (37.87%±1.39%) and green groups (38.35%±1.28%) were significantly higher than those in the blue group (30.15%±3.46%, P<0.05). The red group (5.24±1.91) U/g prot showed significantly higher alkaline phosphatase (AKP) activity than the white group (1.74±0.16) U/g prot, P<0.05, while the white group (144.87±19.38) U/mL had significantly lower catalase (CAT) activity than the red (289.41±13.19) U/mL, blue (258.47±22.17) U/mL, and black groups (218.72±25.79) U/mL, P<0.05. The black group (14.64±0.92) U/mL exhibited significantly higher superoxide dismutase (SOD) activity than the red group (10.45±1.47) U/mL, P<0.05. In conclusion, background color significantly affects the growth performance, personality traits, oxygen-carrying capacity, antioxidant activity, and non-specific immunity of juvenile S. schlegelii, with correlations observed among individual behavioral indicators. The red background induced higher stress levels, whereas the green background improved welfare. This study identifies optimal background colors for juvenile S. schlegelii, enriching theoretical knowledge on how environmental enrichment influences fish behavior and physiology. The findings provide valuable insights for enhancing aquaculture welfare and optimizing breeding techniques.