The Effect of Low Temperature and Fasting during the Winter on Growth and Smoltification of Coho Salmon

This study examined the effect of winter feeding and fasting, under both warm (10°C) and cold (2.5°C) water temperatures, on smoltification of juvenile coho salmon Oncorhynchus kisutch. Treatments were warm–fed, warm–not fed, cold–fed, and cold–not fed during the winter (January–February) before smoltification in March–May. All groups were fed and maintained at 10°C during the smoltification period. The following variables were measured: Fork length, weight, condition factor, smolt-associated appearance, whole-body lipid levels, and gill Na+, K+-ATPase activity. Warm–fed fish grew continuously throughout the winter and were larger than fish from the other treatments. Fish from the other groups showed little or no growth during January and February. Although condition factors decreased significantly in the winter-fasted groups under both warm and cold temperatures, winter whole-body lipid levels and smoltification-associated gill Na+, K+-ATPase activities were not different among groups. These data suggest that winter fasting, even under relatively warm winter water temperatures, may not impair the condition or smoltification of hatchery-cultured coho salmon.