Plasticity of smolting in spring chinook salmon: relation to growth and insulin-like growth factor-I

In two year classes of Willamette River spring chinook salmon, reared at the Willamette Hatchery, and two groups of Yakima River spring chinook salmon, one sampled from the Yakima River and the other reared in a hatchery, fish which had relatively high growth rates in the summer-autumn period smelted in the autumn as measured by increases in gill Na+ K+ ATPase activity. In contrast, groups with relatively low growth rate did not smelt in the autumn. Plasma levels of insulin-like growth factor-I (IGF-I) showed discrete differences between groups, with high levels associated with increased gill Na+ K+ ATPase activities. These results demonstrate that smelting is plastic in spring chinook salmon, occurring in the autumn or the spring. In addition, smelting appeared to be related to growth rate; however, the relationships shown were correlational and causal mechanisms were not elucidated. Yet, the results do indicate a relationship between growth, an endocrine growth meter and smelting, suggesting a mechanistic link between developmental plasticity and the environment mediated by the endocrine system. (C) 1998 The Fisheries Society of the British Isles.