Effects of growth and fatness on sexual development of chinook salmon (Oncorhynchus tshawytscha) parr

The independent effects of size and fatness, 1 year prior to maturity, on male sexual development of chinook salmon (Oncorhynchus tshawytscha) were tested. Beginning in March 1995, ration size and dietary lipid were independently manipulated to produce four groups of spring chinook salmon differing in size and fatness. Size, growth rate, adiposity, Liver triacylglycerol and glycogen contents, and plasma insulin and insulin-like growth factor I (IGF-I) levels were monitored to follow the metabolic states of fish in the different treatment groups and to observe whether plasma levels of these growth mediators predict sexual development. Differences in size and fatness were well established by the first autumn (September 1995), 1 year prior to sexual maturity, and common ration size groups were pooled for further rearing. Subsequently in winter-spring (February-March), 6 months prior to sexual maturity, there were no within-tank differences in size or fatness. Nevertheless, the effects of size and fatness, from I year earlier, on incidence of sexual maturity were significant. Overall, size appeared to have the primary effect, but for smaller fish, an effect of fat content was indicated. Plasma insulin levels, and in limited cases, IGF-I levels, were correlated with growth rate and size, but were not accurate indicators of sexual development.