Dietary fishmeal replacement by black soldier fly larvae meals affected red drum (Sciaenops ocellatus) production performance and intestinal microbiota depending on what feed substrate the insect larvae were offered

This study evaluated the production of two black soldier fly larval meals (BSFLMs) when rearing the larvae on brewers’ spent grains (BSFLM-B) or a commercially available substrate (BSFLM-C, Gainesville house fly diet). The resulting nutrient composition of the BSFLMs were significantly impacted by the feeding substrates, and they were evaluated as a protein ingredient for red drum, where BSFLM-B and BSLFM-C replaced 65% of the fishmeal protein from the control diet. For a comparative feeding trial, three experimental diets were formulated to be isonitrogenous and isoenergetic. Groups of 12 red drum (~ 5 g) were stocked in each of 15, 38-L aquaria, and the three experimental diets were distributed in a completely randomized block design. The experimental diets were offered for 8 weeks at fixed percentage of the body weight that was weekly adjusted. Red drum fed BSFLM-B diets presented impaired weight gain and feed efficiency when compared to the control group. However, red drum fed BSFLM-C diets had growth performance numerically lower, but it was not statistically different than that of fish fed the control diet. Dietary inclusion of BSFLMs significantly affected the whole-body saturated fatty acid composition, total omega-3 and omega-6, and reduced the mineral profile of red drum. The intestinal microbiota was also affected by the dietary BSFLMs, with possible reduction of the relative abundance of a prominent pathogenic bacterial Flavobacterium spp. The findings of the present study highlight the importance of the nutrition of BSFL prior ingredient manufacturing to be a suitable sustainable replacement of forage fishmeal for carnivorous fish, and the potential nutraceutical properties of BSLFMs to possibly combat enteric pathogenic in industrial conditions.