Combining biochemical methods to trace organic effluent from fish farms

The substitution of fish oils and fish meal with terrestrial components in the diets of farmed fin-fish offers a unique opportunity to trace organic effluents from fin-fish aquaculture into the marine environment. In this study, we compared 3 techniques—the detection of soya DNA, fatty acids and stable isotopes—for tracing terrestrial components from fin-fish diets and fecal material passing from a coastal salmonid farm in Norway into the marine environment, i.e. seston traps and sediment, and then into benthic fauna, represented by the king scallop Pecten maximus. We detected soya in both the environment and scallops collected at farm locations, while changes in fatty acid composition and stable isotopes were detected between farm and reference locations in the seston traps and scallops, with great variation among organs in the latter. Combining the 3 techniques provided the greatest accuracy in distinguishing between scallops from farm and re ference locations. Our results show that these 3 techniques offer complementary information on the incorporation of terrestrial components from fin-fish aquaculture into the local environment, and provide support for their potential use as regional environment monitors of aquaculture effluents.