Unravelling the fatty acid profiles of different polychaete species cultured under integrated multi-trophic aquaculture (IMTA)

Abstract

Polychaetes can be successfully employed to recover otherwise wasted nutrients present in particulate organic matter (POM) of aquaculture effluents. The present study describes the fatty acid (FA) profile of four different polychaete species cultured in sand filters supplied with effluent water from a marine fish farm. The FA profile of cultured and wild Hediste diversicolor was compared and revealed a ≈ 24.2% dissimilarity, with cultured biomass displaying a higher content in two essential n-3 highly unsaturated FA (HUFA) (EPA [20:5 n-3] and DHA [22:6 n-3]-eicosapentaenoic and docosahexaenoic acid, respectively). The comparison of the FA profile of cultured H. diversicolor with that of other polychaete species whose larvae successfully settled on the sand filters (Diopatra neapolitana, Sabella cf. pavonina and Terebella lapidaria) revealed that their FA profile, which is here described for the first time, displayed high levels of EPA and DHA (≈ 1.5-4.8 and 1.0-1.1 µg mg^-1 DW, respectively). The highest concentration of total FA per biomass of polychaete was recorded in H. diversicolor and T. lapidaria, with both species being the ones whose FA profiles revealed a lowest level of dissimilarity and more closely resembled that of the aquafeed used in the fish farm. In the present work it was demonstrated that it is possible to produce polychaetes biomass with high nutritional value through an eco-design concept such as integrated multi-trophic aquaculture (IMTA). Indeed, this framework promotes a cleaner production and, in this specific case, allowed to recover essential fatty acids that are commonly wasted in aquaculture effluents.

Figure 1

Fatty acid profile of wild and IMTA-cultured Hediste diversicolor: (a) unsaturated and saturated fatty acids ratio (UFA/SFA); (b) n-3/n-6 highly unsaturated fatty acids ratio (n-3/n-6 HUFA); (c) sum of n-3 and n-6 highly unsaturated fatty acids content (∑n-3 and n-6 HUFA; values in µg mg⁻¹ DW). Average values ± SD (n = 5).

Figure 2

Polychaete species surveyed during the present study: (a) Hediste diversicolor; (b) Diopatra neapolitana; (c) Sabella cf. pavonina and (d) Terebella lapidaria.

Figure 3

Fatty acid profile of different IMTA-cultured polychaetes (Hediste diversicolor, Diopatra neapolitana, Sabella cf. pavonina and Terebella lapidaria): (a) unsaturated and saturated fatty acids ratio (UFA/SFA); (b) n-3/n-6 highly unsaturated fatty acids ratio (n-3/n-6 HUFA); (c) sum of n-3 and n-6 highly unsaturated fatty acids content (∑n-3 and n-6 HUFA; values in µg mg⁻¹ DW). Average values ± SD (n = 5).

Figure 4

Principal coordinates analysis (PCO) of common fatty acids present in the aquafeed supplied to fish being farmed and the four IMTA-cultured polychaetes (Hediste diversicolor, Diopatra neapolitana, Sabella cf. pavonina and Terebella lapidaria) (common with at least one of the species). Average values (± SD) (n = 5). ALA alpha-linolenic acid, ARA arachidonic acid, DHA docosahexaenoic acid, DPA docosapentaenoic acid, EPA eicosapentaenoic acid, ETA eicosatetraenoic acid, ETE eicosatrienoic acid, LA linoleic acid.

Figure 5

(a) Polychaete assisted sand filters (PASF) used in the present study; (b) Hediste diversicolor in sand bed.