The effect of restricted springtime feeding on growth and maturation of freshwater‐reared Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Springtime fasting was used as a means to reduce the incidence of early maturation in freshwater cultured male chinook salmon Oncorhynchus tshawytscha (Walbaum) of New Zealand origin. The experiment was started with yearling fish at the beginning of September (spring) and completed in the following April (autumn) at the time of expected maturation. Feeding was restricted for 2 months (September-October) and 3 months (September-November) by offering food only on alternate weeks. In April, the control group, full fed throughout, had a significantly higher incidence (60%) of mature males then the two groups that had been fasted for 2 or 3 months in the spring. There was little difference in maturation rate in the latter groups (21% and 24%). Growth was depressed during fasting, relative to controls, but the mean weight of the group fasted for 2 months was not significantly different to that of the controls by April.