NUTRITIONAL VALUE OF BLACK SOLDIER FLY Hermetia illucens REARED IN TWO DIFFERENT SUBSTRATES, AND THEIR EFFECT ON GROWTH PERFORMANCE, IMMUNE RESPONSES, AND INTESTINAL MICROBIOTA WHEN PARTIALLY REPLACING FISHMEAL IN DIETS FOR JUVENILE RED DRUM Sciaenops ocellatus

Black soldier fly larvae meal  has been identified as a promising ingredient for  aquafeeds due to its  nutritional composition and high production capacity on relatively low-value substrates . In the current study,  two b lack soldier fly meals were produced when the larvae  were reared in Brewer's spent grains (BSFL-B ) and a commercially available substrate (BSFL-C). Nutrient composition  of the BSFL meals  were significantly impacted by their feeding substrates where the larvae fed spent grains  presented higher lipid and energy contents , and lower ash content than those reared o n  the  commercial substrate.

For the comparative feeding trial, a reference diet was formulated  for red drum  with practical ingredients to be similar to a commercial diet with menhaden fishmeal included at 15.45% of dry weight. T he experimental diets contained the  two larvae meals replacing 65 % of  the menhaden fishmeal  in  the reference diet on an equal weight basis .  Groups of 12 fish (~5.6 g) were stocked in 15, 38-L aquaria, and the three experimental diets were distributed in a completely randomized  block design (n=5). After 8 weeks,  fish fed BSFL-B diets presented  impaired weight gain and feed efficiency (FE) when compared to those fed the reference diet .  Red drum fed BSFL-C diets had growth performance numerically lower, but not statistically different, than the fish fed the  reference diet. H igher mineral  and lower lipid  content  were observed  in whole-body tissues of fish fed  the reference diet when  compared to fish fed either BSFL meals.  The remaining red drum had their intestinal d igesta aseptically collected, and b acterial DNA was extracted to assess  possible  differences in microbial communities using next-generation sequencing (NGS) (Figure 1).  The dietary treatments significantly impacted the intestinal  microbiome  in relative abundances of bacteria and the  predicted functions of the  bacterial metagenome using PICRUSt2. Alpha-  and beta-diversity metrics of the bacterial communities  also were significantly affected by the experimental diets . In conclusion, a  partial replacement of  fishmeal  could be achieved  with BSFL- C  without  significantly  impairing growth performance, and  both BSFL meals  altered  the intestinal microbiome when compared to red drum fed a reference diet.