THE EFFECT OF RESTRICTED SPRINGTIME FEEDING ON GROWTH AND MATURATION OF FRESH-WATER-REARED CHINOOK SALMON, ONCORHYNCHUS-TSHAWYTSCHA (WALBAUM)

Springtime fasting was used as a means to reduce the incidence of earl y maturation in freshwater cultured male chinook salmon Oncorhynchus t shawytscha (Walbaum) of New Zealand origin. The experiment was started with yearling fish at the beginning of September (spring) and complet ed 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 Apri l, the control group, full fed throughout, had a significantly higher incidence (60%) of mature males then the two groups that had been fast ed for 2 or 3 months in the spring. There was little difference in mat uration 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 co ntrols by April.