Tracing fish farm waste in the northern shrimp Pandalus borealis (Kroyer, 1838) using lipid biomarkers

A large amount of organic effluents are released annually from coastal fish farming locations primarily in the form of faeces that settle to the seabed, where they become a substantial food source for benthic communities. The inclusion of marine and vegetable oils as sources of lipids in salmon feed has resulted in a fatty acid (FA) composition that differs markedly from marine-derived material, and thus they can be used as an efficient tracer for the distribution of fish farm waste in both sediments and fish. To obtain a better understanding of the flux of organic fish farm waste through the benthic food web, we sampled northern shrimp Pandalus borealis at fish farming and reference locations in 4 regions along the Norwegian coast. Analyses of the FA compositions of muscular tissue demonstrated that shrimp collected within 800 m from fish farms had a higher content of the vegetable-derived FAs 18: 2n6 (linoleic acid) and 18: 3n3 (alpha-linolenic acid) and the marine FAs 20:1n9 and 22:1n11, compared with shrimp collected from reference locations. This difference in specific FA contents allowed us to separate shrimp collected at fish farming locations from those collected at reference locations. Our results demonstrate that shrimp within the distribution range of fish farms can incorporate organic fish farm waste into part of their diet, either directly through the consumption of waste feed and faeces or indirectly by feeding on influenced infauna.