Potential of the polychaete hediste diversicolor fed on aquaculture and biogas side streams as an aquaculture food source

We evaluated the potential of the marine bristleworm Hediste diversicolor (Polychaeta) to recycle side streams from aquaculture and biogas production. Polychaetes were fed along a gradient from pure aquaculture sludge (SS) to pure solid biogas digestate (SBD) in 33% steps, with a positive control reared on fish feed (FF). Worms fed with FF showed the highest specific growth rate; there were no significant differences in growth rates among worms fed pure SS, pure SBD or their mixtures. While the diets differed significantly in protein concentrations, the worms showed comparable protein concentrations at the end of the 30 d rearing period (42-47% of dry weight). Lipid content in the worms was positively correlated with that in their diets. The worms on mixtures of SS and SBD with different ratios showed similar amino acid profiles. Fatty acid (FA) composition in the polychaetes reflected diet, where increased fractions of SBD resulted in an increase in long-chain polyunsaturated FAs, such as arachidonic (C20:4 n-6) and eicosapentaenoic (C20:5 n-3) acids, whereas increased ratios of SS increased docosapentaenoic (C22:5 n-3) and docosahexaenoic (C22:6 n-3) acids. These results suggest that polychaetes can recycle organic nutrients from aquaculture and biogas side streams into high-quality proteins and lipids, and can potentially serve as ingredients for aquafeeds.