Rearing conditions differentially affect behavioural phenotypes of male “jack” and “hooknose” chinook salmon and their sisters in both fresh and salt water

Alternative reproductive tactics are widespread in fishes. In Pacific salmon, males either become a competitive hooknose, or a sneaker jack, which is undesirable in aquaculture when overabundant. Juveniles often experience accelerated growth prior to becoming jacks, potentially caused by increased competitiveness. We tested the behaviour of hatchery-reared Chinook salmon (Oncorhynchus tshawytscha) in fresh water and after 1 year in salt water. We also tested the effects of freshwater rearing density (100, 50, or 35 fish per 200 L), food ration (high or low), sire (jack or hooknose) for jacks, hooknoses, and females with and without confirmed jack siblings. Sisters of jacks were further identified to test whether females closely related to jacks also showed behavioural differences. Overall, jacks did not behave as predicted; rearing conditions were the strongest determinant of behaviour, and jack sisters behaved differently than jacks and other females. Our study underscores the complexities of jack behaviour, and of females closely related to jacks, at all development stages and supports the use of behavioural screenings to regulate jacking rates in hatcheries by identifying jack sisters