Preliminary investigation on replacing fish meal with integrated multi-trophic aquaculture produced bioflocs in the diets of advanced Red drum (Sciaenops ocellatus, Actinopterygii) juveniles

Abstract

Biofloc technology is a microbially-based water quality strategy in which bacteria transform otherwise toxic ammonia and nitrite into nutritious biomass that may replace proteins in fish diets. Biofloc meal (BM) produced from an ex-situ bioreactor as part of a land-based integrated multi-trophic aquaculture system (LB-IMTA) was incorporated into five isonitrogenous diets consisting of, 1) fish meal (FM)-based control (no BM), 2) BM replacing FM at 25 % (BM25), 3) BM25 with an amino acid (AA) mixture (methionine, lysine, leucine, threonine, and arginine), 4) BM replacing FM at 50 % (BM50), and 5) BM50 with the AA mixture. These diets were fed to Red drum (Sciaenops ocellatus) advanced juveniles (initial weight of 61.5 g) for 8 weeks. Fish fed the BM25 diet had similar growth and feeding efficiency compared to the control, while those fed the BM25AA diet led to significantly faster growth and better feeding efficiency than the control. Fish fed the BM50 experienced negative growth values. While the BF50AA diet had numerically worse growth and feeding efficiency, these values were not significantly different than the control. Whole-body lipid content in fish fed the BM50 and BM50AA diets was significantly lower than the other treatments. Results demonstrate that BM, as a by-product from LB-IMTA, can replace FM without AA supplementation in the diets of advanced Red drum juveniles. Remarkably, replacing FM by 25 % with BM when the AA mixture was included significantly improved Red drum growth compared to those fed the FM-based control diet. These findings demonstrate that BM with AA inclusions may not only improve production but potentially decrease feeding costs while enhancing sustainability in closed recirculating systems. Further research on enhancing the nutritional value of LB-IMTA produced BM may be a worthwhile direction to take advantage of a readily available by-product.