Canthaxanthin as a potential tracer of salmon feed in mussels (Mytilus spp.) and sea urchins (Strongylocentrotus droebachiensis)

► Canthaxanthin used as a potential dietary tracer for salmon aquaculture ► Blue mussel digestive gland effective for short term detection of canthaxathin ► Green sea urchin gonad effective for long term detection of canthaxanthin ► Exponential decline of canthaxanthin signal within 100 m from our studied salmon cage ► Low but constant canthaxanthin signal from 300 m to 1 km from studied salmon cage