Salmonids are characterized by alternative reproductive tactics, which can lead to an asymmetry in relatedness among offspring within nests and consequently the benefit of discriminating among nestmates. In this study, we examined the effect of paternal reproductive tactic on juvenile behaviour and kin discrimination in Chinook salmon. We created maternal half-sibling families by collecting eggs from mature females and fertilizing one-half with the milt of a precocious 2-yr-old male and the other half with the milt of a non-precocious 4-yr-old male. These families were reared in full-sibling groups for approximately 9 mo, and social interactions were then observed in groups of six fish of mixed relatedness. We found evidence for kin discrimination, as significantly less aggression was directed towards related fish than unrelated fish, and the same trends were observed regardless of whether social interactions included full-siblings or half-siblings. These results show that familiarity is not required to recognize kin and thereby implicate phenotype matching as the mechanism of kin recognition. We also found that the offspring of 2-yr-old males were larger and more aggressive than the offspring of 4-yr-old males, which is consistent with other studies showing that precocious males are the fastest-growing members of their cohort. However, kin-directed behaviours did not differ between the offspring of 2- and 4-yr-old males.