Compensatory Growth after Winter Food Deprivation in Hatchery-Produced Coho Salmon and Chinook Salmon Smolts

This study investigated whether coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha smolts would exhibit elevated compensatory growth rates in the spring after food deprivation during the winter. We also tested whether food-deprived fish would attain the same physiological attributes as smolts fed continuously during this period. Replicate treatment groups were deprived of food for 10 and 16 weeks, centered on the winter solstice. Control groups were fed to satiation 2 d weekly during the 10-week deprivation period and every day afterwards. All groups were fed daily to satiation from the end of the deprivation periods until after summer solstice. Treated fish of both species were smaller than controls after deprivation but grew faster after feeding resumed. Growth rates were not significantly different between treatment and control groups until the fish were transferred to seawater. which was 4 degrees C warmer than freshwater at the time of transfer. At the end of the study in July. fish of both species deprived of food for 10 weeks were the same size as controls but fish deprived for 16 weeks remained smaller. Protein content decreased during deprivation while moisture and ash content increased, but the proximate composition of all groups was similar by the end of the study. There was no statistically detectable difference in whole-body lipid between control and treatment groups at any time during the study. Spring increases in gill Na+,K+-ATPase activity were unaffected by deprivation. Although treated coho and Chinook salmon smolts grew faster in the spring, restored their body composition, and did not lose osmoregulatory ability, the life-long effects on size and survival remain unknown.