Feeding black soldier fly larvae (Hermetia illucens) reared on organic rest streams alters gut characteristics of Atlantic salmon (Salmo salar)

Abstract

The Atlantic salmon (Salmo salar) aquaculture industry is growing, and with it, the need to source and optimise sustainable ingredients for aquafeeds. Black soldier fly (BSF) larvae (Hermetia illucens) have received increasing research attention since they are a good source of protein that can efficiently convert a wide range of low-value organic material into valuable resources. This study investigated the impact of three differently processed BSF meals, an untreated BSF diet (BSFC+), a dechitinated BSF diet (BSFC-) and a fermented BSF diet (BSFC+P+) at a 10% inclusion level replacing fish meal in a fish meal control (FM) and a marine and soy protein concentrate based control diet (SPC). Growth performance, gut microbiome and gut histology of salmon fry was assessed. The inclusion and processing methods of BSF showed no adverse impacts on either growth performance or gut histology. However, the gut microbiome of fish was significantly altered by both the protein source and the processing method of the BSF larvae. Fish fed BSFC+, had an increased diversity and evenness of the community compared with conventional protein sources alone, and compared with the other BSF processing methods. However, control diets had a greater presence of lactic acid bacteria and genera associated with faster growing hosts. Fish fed BSF had a high relative abundance of the genus, Exiguobacterium, a chitin-degrading bacterium and in BSFC+P+ fed fish this bacterium completely dominated the community, indicating the presence of dysbiosis. Future studies should determine, why Exiguobacterium has dominated the community for the BSFC+P+ diet, and if it provides a digestive function to the host and identify bacteria that are indicators of optimal host performance and resilience. The results confirmed that BSF is a promising fish meal replacement for salmon, and it demonstrated that BSFC+ has a potential prebiotic impact on the gut microbiome of Atlantic salmon.

Growth performance, hepatic gene expression, and plasma biochemistry of rainbow trout fed full-fat meal, defatted meal, oil and chitin from black soldier flies

“…In agreement, a meta-analysis of 17 studies by Weththasinghe et al (2021) fed BSF to rainbow trout and Atlantic salmon and found feeding between 5-60 % BSF in the diet or between 0-100 % replacement of fishmeal resulted in similar or improved growth performance compared to the control. Similar results have been found previously when BSF replaced animal-based protein in diets for Atlantic salmon that resulted in similar or improved growth and FCR [ 13 ]. In addition, another meta-analysis of 33 studies where several fish species were fed insects suggested a maximum inclusion of up to 29 % BSF [ 14 ].…”

“…These changes in leukocyte numbers have been largely attributed to the indirect effects of the gut microbiome that feed off chitin and chitosan, and interact with the host immune system [ 44 ]. In addition, a study that fed an untreated BSF diet to Atlantic salmon found that the gut bacteria had increased diversity and evenness of the community compared to the salmon fed dechitinated and fermented BSF diets [ 13 ]. As such, it was expected that the 1 % chitin diet as well as the other BSF diets, except 4 % BSF oil, would have extensively modulated gene expression.…”

The Salmon Microbial Genome Atlas enables novel insights into bacteria-host interactions via functional mapping

“…At a 97% identity cut-off when comparing SMGA 16S rRNA sequences to amplicon sequence variants (ASVs), 144 out of 146 SMGA bacteria were detected in publicly available 16S rRNA gene datasets from either in vivo trials or in vitro models with salmon gut microbial communities, as well as datasets generated within this study (ImpTrial1 and ImpTrial2) (Supplementary Fig. S3) 10, [25][26][27][28][29][30][31][32][33][34] . SMGA bacteria were detected in microbiomes not only from Norwegian salmon populations, but also in gut samples from wild and farmed Atlantic salmon retrieved from Scotland 27 , the UK 28 and Chile 34 .…”

Introducing the special issue ‘Application of insect ingredients in sustainable aquaculture’

“…However, the gut microbiome of fish was significantly altered by both the protein source and the processing method of the BSF larvae. In particular, the research showed a very interesting potential prebiotic impact of the fermented BSF meal (Leeper et al, 2022).…”