Black soldier fly larvae (Hermetia illucens) meal is a viable protein source for Atlantic salmon (Salmo salar) during a large-scale controlled field trial under commercial-like conditions

Abstract

Black soldier fly larvae meal (BSFL) from Hermetia illucens is a promising alternative protein source in diets for farmed fish. The larvae can efficiently convert low-value organic material into high-value protein in a production cycle with low arable land and freshwater inputs. A few recent studies have shown that BSFL is a suitable protein source for Atlantic salmon (Salmo salar) in smaller controlled experiments. However, industry-relevant field trials conducted under large scale near-commercial conditions over a longer period are lacking. In this study, a feeding trial was performed to evaluate the impact of BSFL on growth performance and health of Atlantic salmon during the grow-out phase in seawater, in a commercial site in Vestland county, Norway. A total of 181,046 post-smolt Atlantic salmon were distributed into six duplicate sea cages and fed one of three diets (commercial-like control diet and two test diets partially replacing the protein content of the control diet with 4% and 8% defatted BSFL meal) for 21 weeks, until a relevant commercial slaughter size of 4.5–5.0 kg was reached. Health parameters were assessed, including histology of the distal intestine (DI), DI microbiota identification (by 16 s rRNA-seq) and salmon RNA-seq of DI and head kidney (HK). The results showed that the inclusion of BSFL meal supported growth performance and had no adverse effect on gut health. The beta diversity of the DI microbiota and the relative abundance of families Lactobacillaceae and the chitinolytic Bacillaceae increased in the fish fed the BSFL diets. Additionally, no histopathological changes were attributable to BSFL meal intake. Results from RNA-seq in DI revealed that BSFL inclusion modulates metabolic processes associated with lipids, response to estrogens, activity of immune receptors (to chemokines), phagocytosis and extracellular vesicles. Based on these results, black soldier fly larvae meal was shown to be a suitable alternative protein ingredient in inclusions of up to at least 8% for Atlantic salmon under industrial fish farming conditions.