Adult three-spined sticklebacks prefer to shoal with familiar kin. Behaviour 141

Theory predicts several advantages for animals to shoal with kin or familiars such as the evolution of altruistic behaviour or the reduction of competition because of more stable dominance hierarchies. In three-spined sticklebacks, Gasterosteus aculeatus, the influence of kinship and familiarity on shoaling decisions is ambiguous. We tested the potential for kin recognition of laboratory-bred adult, reproductively non-active sticklebacks in an experimen-tal design in which a testfish was given the choice between two different shoals. One shoal consisted of its familiar full sibs while the other one was composed of fish unfamiliar and unrelated to the testfish. The time that testfish joined each group indicated that adult, repro-ductively non-active sticklebacks prefer to shoal with familiar relatives. Characteristics of the group such as measured by body mass, standard length, and body condition of its members did not significantly explain the shoaling preference for familiar kin