Temperature modifies activity, inter-individual relationships and group structure in a fish

A host of abiotic factors modify fish social behavior. However, few studies have characterized the effects of temperature on behavior. In this study, brown trout Salmo trutta fry were reared at 5 dif- ferent temperatures （4℃, 6℃, 8℃, 10℃, and 12℃）. In order to characterize group structure, 3 be- havioral parameters were investigated： group social structure （based on inter-individual distances）, inter-individual relationships （based on physical contacts）, and individual activity. These behavioral parameters were studied at the emergence stage, which corresponds to a switch from a social gre- garious life in the gravel to a solitary one in the water column. Data analysis showed that the inter- individual distances increased with increasing temperature, particularly the nearest neighbor distance. The mean number of physical contacts between fry increased at both low and high tem- peratures. At high temperatures, most fry moved apart from each other after a physical contact. Swimming activity decreased at both the lower and upper temperatures （18% of activity at 4℃, 38% at 8℃, and 12% at 12℃）. This study showed that temperature modifies brown trout fry activity, inter-individual relationships, and social behavior, which all affect group cohesion before emer- gence and can influence their survival and dispersal.