Does presmolt growth rate in steelhead trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) predict growth rate in seawater?

The dependence of growth rate in postsmolts in seawater on presmolt growth rate was examined in steelhead trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch). Presmolt growth rate explained a significant but small proportion, 16% for steelhead and 6% for coho, of the variation in growth rate in seawater. The relationship between presmolt and postsmolt growth rate was positive for steelhead and slightly negative for coho. In steelhead trout, the relationship between freshwater and seawater growth rate was not affected by male parental type (steelhead or domesticated rainbow trout). In coho salmon, however, the slope of regression was affected by differences among family groups. These results demonstrate variable relationships between presmolt and postsmolt growth rate among salmonid species and families, suggesting that fast presmolt growth is not necessarily associated with fast seawater growth in hatchery-reared salmonids. These findings are of interest for rearing procedures in smelt hatcheries and for models predicting optimal time and size for migration in wild smelts.