Differential responses of kin and nonkin salmon to patterns of water flow: does recirculation influence aggression?

Studies conducted in laboratory streams have shown that juvenile salmonid fish (parr) can differentiate between their kin and nonkin and may be less aggressive towards their kin. Chemicals produced by salmonids are also known to be used as cues to aid kin recognition. We tested the hypothesis that the ability of Atlantic salmon, Salmo salar, to recognize kin and hence modulate their level of aggression is influenced by the amount of water recirculation, which would be expected to affect the concentration of odour. Levels of aggression were similar between pairs of kin and pairs of nonkin when there was negligible recirculation of water. However, when water was recirculated, pairs of nonkin were on average 1.56 times more aggressive than pairs of kin, owing to an increase in attacks by the dominant fish. The data do not support the idea that odour concentration affects kin recognition and hence reduces aggression among siblings. Instead they indicate that recirculation of water instigates heightened aggression in dominant fish but only towards nonkin subordinates. The study suggests that the advantages for juvenile salmonids of associating with kin vary spatially, being influenced by water flow dynamics.