Social Environment Shapes Color Choice: Differential Preference in Young <i>Coreius heterodon</i>

Abstract The color preference of juvenile bronze gudgeon (Coreius heterodon), an endemic fish species in the Yangtze River, remains poorly understood despite its importance for animal welfare and aquaculture. In this study, color selection behavior was assessed across six background colors (red, yellow, blue, green, black, white) under both isolated and grouped social conditions, using a six-arm radial maze. The results reveal that juvenile C. heterodon exhibit a strong and consistent preference for yellow-green backgrounds and distinct avoidance of black-red, regardless of social context, with these behaviors likely rooted in early imprinting, that is, fixed responses formed without the need for subsequent reinforcement. Social condition was found to modulate responses to white and blue, shifting white from slightly attractive to neutral/aversive and blue from aversive to attractive. These findings directly inform aquaculture practice, suggesting that establishing yellow-green substrates while minimizing black-red areas is advisable. Presumably, pre-release acclimatization based on imprinting mechanisms would shorten natural acclimatization time and enhance post-stocking survival. Our findings provide a scalable, behaviorally-informed framework for optimizing welfare and production in C. heterodon and related species.