Hermetia illucens (also known as Black Soldier Fly - BSF) is one of the most widely used insect species for producing insect meal and replacing fishmeal (FM) in aquafeeds. It can be reared on a wide variety of biowaste. The nutritional composition of rearing substrate is extremely important for an efficient BSF growth, and it can modulate the insect meal nutritional value. In turn, insect meal nutritional profile may affect fish performance. To this regard, few studies have been carried out. Hence, the purpose of this study was to investigate the effects of partially or totally FM replacement, with larval meal obtained from BSF reared on strawberry by-products (SB) and spent grain (SG), on fish growth performance and gut health.
To this purpose, 375 double transgenic zebrafish Tg(coro1a:eGFP;lyz:Dsred) were used as fish model, and macrophages and neutrophils were distinguished by green and green and red fluorescence, respectively. The experimental period lasted 42 days and five isoproteic, isolipidic and isoenergetic experimental diets were used: a control diet (CTRL) containing FM, and four experimental diets (SB25, SB35, SG25 and SG35) where 71% or 100% of the FM was replaced with BSFLM (Black Soldier Fly larval meal) obtained from larvae fed on SB and SG, respectively. At the end of the trial, confocal imaging analysis on the anterior intestine was performed to assess macrophages and neutrophils density (n/ µm2). mRNA expression analysis of gata4, nfkb1, pht1 genes (intestinal inflammation markers) was also performed on the caudal intestine portion.
The results showed no negative effects of BFSLM on fish mortality, feed intake, and feed conversion rate; moreover fish fed BSFLM showed higher growth performance (BWg, SGR and Kf) than the control (Figure 1). No differences were observed also for macrophages and neutrophils density as well as for gata4, nfkb1, pht1 expression. However, these genes showed to be downregulated in fish fed on BSFLM, even though not significantly (Figure 2).
However, it may be of interest to better understand the interactions between insect rearing substrate compositions and the possible different uses in aquafeeds.
In conclusion, the results suggested that using Hermetia illucens larvae meal for replacing fishmeal in aquafeeds, enhances fish growth performance, regardless of the type of substrate used.