The effect of temperature on the collective behavior of crucian carp (Carassius auratus) is related to context

Group living is ubiquitous in the animal kingdom and confers a number of benefits and costs. In nature, animal habitats are complex, diverse, and constantly changing. As one of the most important ecological factors, temperature can act directly on the physiology and behavior of ectotherms, and its effect might be related to the context. Here, we used crucian carp (Carassius auratus) as an animal model to investigate how the individual and collective behaviors of the fish respond to two different temperatures (15 °C vs. 25 °C) across three contexts (e.g., open water, food, and food + shelter). Compared to those at 25 °C, the fish at 15 °C had lower individual swimming speed, synchronization of speed, group speed, and longer time spent in the shelter with a lower foraging speed, but such effects of temperature were not found in terms of collective behavior (e.g., interindividual distance, nearest neighbor distance, distance to group center, or group polarization). The individual swimming speeds of the fish increased with increasing environmental complexity at both temperatures. The fish shoals had a higher foraging speed and better group coordination and cohesion in the food context than in the food + shelter context. In the food + shelter context, fish spent time on moving in and out the shelter under a pattern of high swimming speed. Consequently, groups are less efficient at foraging in food + shelter contexts than in food contexts at only 25 °C. Our results suggest that the effects of temperature on the individual and collective behavior of fish are dependent on context.

Establishing how collective behavior emerges is crucial to our understanding of animal societies. The collective behavior and structure of animal groups may change considerably depending on the context, which can alter collective behavior through adaptive changes in individuals’ behavior. Among the various environmental factors, temperature is an ‘ecological master factor’ that influences individuals’ physiology and behavior. Shoals of crucian carp exhibit distinct patterns of response to temperature between individual- and group-level behaviors across contexts. In the food + shelter context, fish at 15 °C spend more time hiding within the shelter, resulting in a lower foraging speed and a longer latency to forage with a smaller group size than those of fish at 25 °C. Our study provides new insights into the consequences of ambient temperature on the collective behavior of group-living animals in nature.