Dietary effects on the fatty acid signature of whole Atlantic cod (Gadus morhua)

Understanding the influence of dietary fatty acids on whole fish is necessary to evaluate the degree to which fatty acids may be used for understanding foraging patterns in fish, as well as in marine mammals that consume their prey whole. Adult Atlantic cod (Gadus morhua) were fed two prey items that differed significantly in fat content and fatty acid compositions. Cod were first fed squid (Illex illecebrosus, 2.0% fat) for 6 weeks, followed by Atlantic mackerel (Scomber scombrus, 15.7% fat) for 8 weeks. Twenty whole cod were individually analyzed at each of 0, 3, 6, 11, and 14 weeks. Despite being on a low-fat squid diet, in only 3 weeks, cod fatty acid patterns changed significantly to reflect the patterns found in squid and did not further change at 6 weeks. When switched to a high-fat mackerel diet, total body fat of cod increased and the fatty acid composition of cod changed significantly in the direction of patterns found in mackerel. Despite changes in cod fatty acid signatures, cod were readily distinguished from the fatty acid signatures of their diets. Our results provide support for the use of fatty acids as indicators of diet at upper trophic levels.