Evaluation of Endocrine Indices of Growth in Individual Postsmolt Coho Salmon

Abstract

Plasma levels of the hormones insulin and insulin-like growth factor-I (IGF-I) were assessed as indices of growth for individual juvenile coho salmon Oncorhynchus kisutch. Smolts were tagged in April, introduced to seawater in May, and reared at two different feeding levels. Fish lengths and weights were obtained in June, August, September, and November. Plasma samples were obtained in September and November. There was a consistent, robust relation (over both feeding rates and sampling dates) between plasma IGF-I and the instantaneous growth in length of individual fish when growth was measured over a 6-week period. There was no consistent association between plasma insulin level and growth, size, or condition factor. Plasma IGF-I levels were also measured in postsmolt coho salmon captured in September from the Strait of Georgia and Puget Sound and were found to be similar to those in laboratory fish.