SOCIAL DYNAMICS IN SALMONID FISHES - DO KIN MAKE BETTER NEIGHBORS

Kin discrimination has been reported in a number of animal taxa, including fish; however, functional explanations for this ability have not been examined. To determine whether kin discrimination has an effect on the social dynamics in Atlantic salmon, Salmo solar, and rainbow trout, Oncorhynchus mykiss, groups of full-siblings and unrelated juveniles were studied in an artificial stream tank. Both species have been previously shown to discriminate kin. The form and frequency of aggressive interactions, and the mean distance to nearest neighbours was recorded. Mean frequency of aggressive interactions was found to be significantly higher in non-kin groups of both species compared with kin groups, and the mean distance to nearest neighbour was significantly lower in kin groups. In addition, kin groups used a significantly lower proportion of 'overtly aggressive' territorial defence modal action patterns and a significantly higher proportion of 'passive' territorial defence modal action patterns compared with non-kin in both species. These results suggest that inclusive fitness benefits may be associated with maintaining territories near kin versus non-kin conspecifics. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.