Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss)

Authors: FAWOLE, FEMI - University Of Idaho; LABH, SHYAM - University Of Idaho; HOSSAIN, MOHD - University Of Idaho; Overturf, Kenneth - Ken; SMALL, BRIAN - University Of Idaho; Welker, Thomas; HARDY, R - University Of Idaho; KUMAR, VIKAS - University Of Idaho

Submitted to: Animal Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2021
Publication Date: 10/11/2021
Citation: Fawole, F.J., Labh, S.N., Hossain, M.S., Overturf, K.E., Small, B.C., Welker, T.L., Hardy, R.W., Kumar, V. 2021. Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss). Animal Nutrition. 7(4):1360-1370. https://doi.org/10.1016/j.aninu.2021.07.008.
DOI: https://doi.org/10.1016/j.aninu.2021.07.008

Interpretive Summary: The primary protein and oil source for fish feed has traditionally been from ocean catch fisheries (e.g. anchovy, menhaden, etc.). Because these resources are dwindling, other sources for fish feeds are needed, and protein and oil from plants and oil seeds have been the primary alternative ingredients. A new potential source for fish oil replacement in fish feeds is insect oil, such as that from black soldier fly larvae (BSFL). The amount of oil in feed and its fatty acid (FA) composition affects the fat deposition in fish flesh, which has been observed in rainbow trout fed 100% alternative sources of oil as a fish oil replacer. Bile acids (BA) naturally solubilize dietary fat and are critical for digestion and absorption of fats in fish and other vertebrates. Bile acids could be used to improve the efficiency of lipid digestion, thereby reducing excess lipid deposition in fish and improve the FA profile. In this study, practical rainbow trout feeds were formulated with either 100% fish oil, soybean oil, insect oil (IO) from BSFL, or IO + supplemented BA as the fat source. Oil source did not affect growth performance of rainbow trout or the deposition of heart healthy, n-3 polyunsaturated fatty acids (PUFA). It was concluded that IO could be used as 100% replacement for fish oil in rainbow trout feeds without negatively affecting fish growth or potential human health benefits.

Technical Abstract: Alternative sources of fish oil are one of the major problems in aquaculture; therefore, the goal of the present study was to examine insect oil (IO) as a potential replacer of fish/soy oil in rainbow trout (Oncorhynchus mykiss) feed. Four diets were formulated wherein fish oil (FO; standard, control diet) was completely replaced with either soybean oil (SO) or IO, and an additional IO-based diet supplemented with 1.5% bile acid (IO+BA) was also evaluated. Three-hundred trout juveniles were randomly stocked into tanks and fed for 10 weeks. Growth performance of IO fed group is similar to FO and SO fed groups, whereas the lowest growth was observed in IO+BA group. Oil sources did not affect the major nutrient content of whole-body, however, the fatty acid composition of the muscle and liver was influenced, with significant changes in total saturated fatty acid detected in IO or IO+BA fed trout compared to the others. But significant changes were noted in omega-3 fatty acid ratios between the groups. Gene expression for genes related to fatty acid utilization were found to be lower in the liver in the FO group, and some were found to be significantly higher in the IO+BA group. Supplementation of BA in the IO diet increased expression of anti-oxidant genes compared to the other groups. In conclusion, IO could serve as a substitute for FO and SO in rainbow trout diet without negatively impacting growth performance.