Chinook salmon (Oncorhynchus tshawytscha) parr undergo a physiological transformation called smoltification that pre-adapts these fish for their transition from freshwater rivers to the saltwater ocean. While this occurs once annually and at a specific season in salmon in the wild, out-of-season spawning of farmed salmon imposes seawater transfer onto parr at unusual time points and under differing environmental conditions (e.g. temperature, photoperiod). This study is examining whether differences are occurring in smoltification between individuals from three different cohorts, i.e., an in-season (reaching target smolt weight between Oct and -Dec), a late-season (Dec-Jan) and an out-of-season cohort (Apr-Jun). Fish were sampled at commercial hatcheries every third week throughout their freshwater growth phase from around 4 g to their saltwater -transfer weight of 30 g; a final sampling was done at 60 -days post transfer at saltwater grow-out pens. We determined biometric parameters including length, body weight, standard growth rate, condition factor (K) and hepatosomatic index (HSI). Additionally, we assayed for blood plasma osmolality, for gill mRNA levels of both subunits (α1a –freshwater, α1b – saltwater) encoding the salt-regulating enzyme Na+/K+-ATPase-α1 (α1a – freshwater, α1b – saltwater) and for gill Na+/K+-ATPase activity. Initial observations indicate that the biometric parameters of the out-of-season cohort were more variable than those of the in-season cohort. Additionally, the presence of abnormal livers (white colouration and “crumbly” texture) across almost all sampling sessions has indicated the need for analysis of the metabolic function of these affected fish. We anticipate that our findings will assist the New Zealand salmon farming industry with making of informed decisions in the management of chinook salmon juveniles prior to seawater transfer.