The Effects of Growth on Development of Precocious Male and Smolts in Sockeye Salmon

BAN Masatoshi

doi:10.11233/aquaculturesci1953.55.507

The effects of alterations in growth on the incidence of precocious male maturation (PM) and seawater tolerance of sockeye salmon (Oncorhynchus nerka) were investigated. Juvenile sockeye salmon were separated into four groups (Groups A-D) and reared under different feeding regimes from November of age-0 to May of age-1. The growth regimes of groups A, B, C and D were the following: low growth throughout the duration, low from November to March and high from March to May, high from November to January and low from January to May, and high throughout the duration, respectively. The PM was determined by gonadosomatic index in May. Seawater tolerance was examined by monthly measurement of gill Na⁺, K⁺-ATPase (ATPase) activity. Proportions of PM among male fish of the groups A, B, C and D were approximately 0%, 50%, 80% and 80%, respectively. The ATPase activities of group-A remained consistently low, while that of the groups B, C and D was elevated significantly in April unrelated to differences of mean fork length and past growth. These results indicate that high growth in early winter of age-0 induces PM and consistent low growth during winter and spring hinders development of both seawater tolerance and smolt development.

The Effects of Growth on Development of Precocious Male and Smolts in Sockeye Salmon

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