Insect (black soldier fly, Hermetia illucens) meal supplementation prevents the soybean meal-induced intestinal enteritis in rainbow trout and health benefits of using insect oil

Authors: KUMAR, VIKAS - University Of Idaho; FAWOLE, FEMI - University Of Idaho; ROMANO, NICHOLAS - University Of Arkansas At Pine Bluff; HOSSAIN, SAKHAWAT - University Of Idaho; LABH, SHYAM - University Of Ilorin; Overturf, Kenneth - Ken; SMALL, BRIAN - University Of Idaho

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2020
Publication Date: 12/19/2020
Citation: Kumar, V., Fawole, F., Romano, N., Hossain, S., Labh, S., Overturf, K.E., Small, B. 2020. Black soldier fly (Hermetia illucens) larvae (BSFL) supplementations prevented soybean meal-induced intestinal enteritis in rainbow trout and benefits of using BSFL oil. Fish and Shellfish Immunology. 109:116-124. https://doi.org/10.1016/j.fsi.2020.12.008.
DOI: https://doi.org/10.1016/j.fsi.2020.12.008

Interpretive Summary: The aquaculture industry continues to expand globally, and this has led to an upward rise in the demand for protein and lipid sources which in the past was supplied by fishmeal and fish oil. The use of plant proteins and oils as sustainable replacements has been difficult because inclusion at higher levels leads to reduced growth and liver and intestinal problems. Black soldier fly larvae (BSFL) and oils derived from BSFL (BSFLO) have been studied as possible replacements to fishmeal and fish oil and their potential to reduce the negative impacts of high plant protein in plant based aquaculture feeds. The addition of BSFL, at low levels decreased the development of intestinal inflammation in diets containing high levels of soybean meal as a protein source. The total replacement of fish oil or soybean oil with BSFLO led to no histopathological changes in the liver or intestine, decreased inflammation and improved immunity based on the gene expression and evaluation of specific immune parameters. These findings will likely increase the demand for BSFL and BSFLO as sustainable products to become a standard ingredient in the diets of rainbow trout. Moreover, these results appear to indicate that it may not be necessary to defat BSFL, which can reduce costs when added to rainbow trout feeds.

Technical Abstract: Black soldier fly larvae (BSFL) and their oils (BSFLO) are receiving increasing attention as sustainable ingredients in fish feeds, but mostly as replacements to marine sources. There were two aims of to this study; in exp. 1, soybean meal (SBM)-based diets were formulated to contain BSFL as supplements at 0 (SBM), 6 (SBM+BSFLlow) or 18% (SBM+BSFLhigh) with a control diet being fishmeal-based (FM). In exp. 2, diets included only fish oil (FO), soybean oil (SBO), BSFLO or BSFLO + bile acid (BA), and all lipid sources were added at 16%. Both experiments were run at the same time and fed to rainbow trout with each treatment being triplicated. After 10 weeks the fish were sampled for liver and distal intestine histology, expression of genes responsible for inflammation in the intestine and kidneys, and serum peroxidase and lysozyme activities. In exp. 1, supplementations of BSFL effectively prevented SBM-induced intestinal enteritis, down-regulated intestinal prostaglandin and interferon regulatory factor, while the SBM+BSFLhigh diet significantly increased serum lysozyme activity. In exp. 2, BSFLO caused no histomorphological change to the liver or intestine, but kidney interluekin-8, tumor necrosis factor and interferon regulatory factor were significantly upregulated along with significantly higher serum peroxidase activity. The inclusion of BA in the BSFLO diets significantly upregulated intestinal prostaglandin gene expression. Overall, BSFL supplementations of 6 or 18% prevented SBM-induced intestinal enteritis based on histological observations, which was supported by a down-regulation in pro-inflammatory genes and enhanced innate immunity. Meanwhile, the use of BSFLO showed some immunological benefits. Therefore, these sustainable resources are recommended in the diets of rainbow trout, especially when using elevated levels of plant-based proteins.