Influence of food regimes and seasonality on fatty acid composition in the ragworm

Nereidid worms are well known to be key prey species for aquatic organisms, including economically important fish (e.g. plaice) and invertebrates (shrimps). Food regimes which include nereidids improve the reproductive fitness of cultured animals, i.e. the 'nereidid effect'. Aquaculture produces huge amounts of sludge, which might be recycled by feeding to the ragworm Nereis diversicolor. Here we analysed the fatty acid profiles in N. diversicolor over 1 yr for a wild population and for ragworms fed with commercial fish food or eel sludge. The omega-3 ([omega]-3) eicosapentanoic acid (20:5n3) was the most abundant fatty acid followed by palmitic (16:0), stearic (18:0) and oleic (18:1) acids. Biomass of the ragworms increased by 205% in worms fed with fish food and remained stable in worms fed with eel sludge, indicating the good adaptation of individuals to the culture conditions. Only under fish food regimes were significant increases observed in saturated and total unsaturated fatty acids compared to natural food regimes. However, the [omega]-3 polyunsaturated fatty acids did not differ among food regimes, indicating that sludge from aquaculture is a good nutritive resource for N. diversicolor. This suggests the potential use of ragworms in aquaculture to reduce the production of waste and increase the reproductive fitness of cultivated animals.