Effects of Dietary Fatty Acids on Juvenile Salmon Growth, Biochemistry, and Aerobic Performance: A Laboratory Rearing Experiment

Juvenile salmon undergo important physiological and ecological transitions as they migrate from freshwater to the ocean, a phase characterized by rapid growth and high mortality. It is becoming increasing clear that variations in nutritional quality of marine prey may be as important as prey quantity in determining salmon survival during this critical period in their life history. Growth potential, and hence survival, may be related to the size when salmon first become piscivorous. We tested the hypothesis that prey nutrient composition and predator nutritional history affects growth, biochemistry, and performance in a population of subyearling Chinook salmon (Onchorynchus tshawytscha). Salmon were reared for 12 weeks on three energetically similar experimental diets. Diets were created with ratios of docosahexaenoic acid (DHA) to eicosapentaenoic acid (EPA) of 0.56, 0.94, and 1.47 by altering the amount of krill, anchovy, and two fatty acid supplements. Tagged salmon reared on the high DHA:EPA anchovy diet trended towards faster growth (0.33±0.05 mm d^-1) compared to fish reared on the low DHA:EPA krill diet (0.27±0.03 mm d^-1) or blended diet (0.29±0.02 mm d^-1). Tissue turnover in salmon, measured in half-lives, was 5 to 28 days for essential fatty acids, and 9 to 184 days for bulk isotopes of nitrogen and carbon, indicating that predator tissue fatty acids reflect diet sooner than stable isotopes. After the rearing experiment, salmon were starved for 4 weeks and their critical swimming speeds measured to determine whether nutritional history had an affect on aerobic performance. Although there were no significant differences in swim performance among diet treatments, there was a significant relationship (r²=0.57, p=0.02) between swimming speed and an individual’s size and storage lipids across diet treatments. Results from this study will support future ecological studies of migrating juvenile salmon and quantitative estimates of diet in other anadromous fish.