Carotenoids of sea lice (Lepeophtheirus salmonis) as potential indicators of host Atlantic salmon (Salmo salar L.) origin

Carotenoid pigment composition of sea lice (Lepeophtheirus salmonis) was compared in samples taken from wild salmon (Salmo salar L.) from the river North Esk and salmon fed on an artificial diet in a fish farm. Pigment was also extracted from sea lice egg strings. Two pigment peaks could be identified in the chromatograms (HPLC)-astaxanthin, normally considered characteristic of wild salmon, and canthaxanthin, the pigment fed to farm fish. The ratio of canthaxanthin-like pigment to astaxanthin (C:A ratio) was 45:1 in farm lice and 8:1 in wild lice. Carotenoid content therefore could potentially be used as a tracer of origin of sea lice in epidemiological investigations. Considerable variability of pigment concentrations in both farm and wild lice may make interpretation difficult. (C) 1997 International Council for the Exploration of the Sea.