The use of biorefinery by-products and natural detritus as feed sources for oysters (Crassostrea gigas) juveniles

Abstract New research is currently underway to explore the potential of macroalgae for the production of biofuels. Marine biofuels in general and macroalgae in particular, offer a number of advantages over terrestrial biofuels including reduced competition for freshwater resources and for land use. Sugars can be extracted from macroalgae and processed into biofuels by anaerobic digestion and fermentation. This process generates significant waste biomass, which, if used, could improve the economic sustainability of the biorefinery sector. Bivalves' aquaculture relies heavily on the production of unicellular algae to feed juvenile individuals and this can represent a bottleneck for the bivalve industry especially in locations where sunlight is limited. Previous research explored the use of macroalgae derived digestate as alternative or integrative feed for juvenile bivalves, exploiting the notion that organic particulate matter (detritus) is an integral part of this animal class natural diet. The prospect of using waste products from the emerging biorefinery industry to solve a bottleneck for aquaculture businesses and, by so doing, improving profitability of both, is an exciting one. In this paper we describe the main nutritional profiles (Protein, Lipid, Carbohydrates and Fatty acids) of the tested diets and investigate the potential for the use of a biorefinery a by-product as replacement option for bivalves' production, by benchmarking it against aquaculture industry standards (live microalgae and commercially available algae paste) and natural detritus constituted by farmed sea urchin digesta. Both the digestate and the natural detritus supported the survival and growth of bivalve spat, especially when used at 50% inclusion rate, over the course of 4-week preliminary trials. Data suggest that a synergistic effect of the nutritional profiles of the diets employed may underpin the observed results. Statement of relevance With this study we compare the biochemical composition and suitability as oyster feed of the Single Cell Detritus produced by S. latissima enzymatic saccharification and natural detritus produced by sea urchin digestive action, with live microalgae as well as commercial algae paste. A comparison between biochemical composition and suitability as aquaculture feed between biorefinery by-products and natural detritus was, to our knowledge, lacking. Results indicate that both the digestate and the natural detritus supported the survival and growth of oyster spat, especially when used at 50% inclusion rate, over the course of 4-weeks trial.