Bioconversion of aquaculture waste blended with vegetable by-products using Hermetia illucens larvae: Process parameters and larval quality

The constantly increasing aquaculture production generates high amounts of biowaste worldwide, which must be properly treated in order to keep aquaculture’s footprint low. This study aimed at evaluating the bioconversion of aquaculture waste streams (RAS sludge, fish trimmings, and harvest macroalgae waste) using black soldier fly (Hermetia illucens, BSF) larvae and the quality of the resulting larval biomass. The study was conducted in a modified shipping container simulating a large-scale setting and the diets were formulated using brewery spent grains and cabbage as base, mixing in aquaculture waste, aiming to treat the highest inclusion rate possible. A bioconversion efficiency of above 20 %_DM and a material reduction generally above 55 %_DM were observed, while generating a larval biomass that was rich in protein (> 35 %_DM), essential amino acids and fatty acids. The larvae reared on fish trimmings (from an anchovy processing plant) had the highest crude fat content (29.0 ± 1.1 %_DM) in relation to other treatments, while the macroalgae waste dietary inclusion generated larvae with low fat content (14.7 ± 1.5 %_DM on average). Interestingly, it was observed that the addition of aquaculture wastes, even in small inclusion levels (between 15 % and 25 % on wet basis), reduced the concentration of saturated fatty acids in the larvae (especially lauric acid and pentadecanoic acid). It was concluded that BSF larvae are able to bioconvert varied aquaculture waste streams and it is possible to produce tailored larval biomass by adding such waste streams in their diets, enabling the production of a protein ingredient with specific traits to be used in aquafeeds.