Insect larvae meal as a complementary functional ingredient in high soybean meal-based diets improve the health of rainbow trout (Oncorhynchus mykiss)

Authors: MA, JIE - University Of Idaho; SINGHA, KRISHNA - University Of Idaho; ABANIKANNDA, MOSOPE - University Of Idaho; MYRSELL, VERONICA - University Of Idaho; Romano, Nicholas; KOUTSOS, ELIZABETH - Enviroflight Llc; ADAMS, DANIEL - Enviroflight Llc; CAIN, KENNETH - University Of Idaho; KUMAR, VIKAS - University Of Idaho

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2025
Publication Date: 5/17/2025
Citation: Ma, J., Singha, K., Abanikannda, M.F., Myrsell, V., Romano, N.P., Koutsos, E., Adams, D., Cain, K.D., Kumar, V. Insect larvae meal as a complementary functional ingredient in high soybean meal-based diets improve the health of rainbow trout (Oncorhynchus mykiss). Journal of Fish Diseases. e14153. 2025. https://doi.org/10.1111/jfd.14153.
DOI: https://doi.org/10.1111/jfd.14153

Interpretive Summary: Soybean meal (SBM) is the most commonly used plant protein in formulated fish diets. However, there are limits to the inclusion of dietary SBM in salmonids and other carnivorous fish because these cause intestinal inflammation that causes disruptions to health, nutrient utilization and subsequently growth. In this study, rainbow trout were fed diets containing black soldier fly larvae (BSFL) meal, either defatted or not, at different levels and compared with a fishmeal-based control diet. The hypothesis was that BSFL meal could mitigate intestinal enteritis in rainbow trout and enhance their resistance to a bacterial pathogen. Results demonstrated that fish fed diets with BSFL led to significantly better resistance to the pathogen along with reduced intestinal inflammation based on histological observations. The non defatted BSFL led to the best outcomes, likely due to lauric acid in the BSFL meal that are known to have health benefits in fish. Thus, the inclusion of BSFL can help replace SBM as a dietary ingredient while improving fish health.

Technical Abstract: This study explores the integration of black soldier fly larvae (BSFL) as a complementary functional ingredient to increase the soybean meal (SBM) inclusion in rainbow trout (Oncorhynchus mykiss) diets. Six experimental diets were formulated, including a control diet as fishmeal (FM), an SBM-based diet, and 2.5 and 5% whole-body (WB) or defatted (DB) BSFL-supplemented SBM-based diets. Results revealed that BSFL inclusion positively influences gut health, immune response, and survival rates following challenge with Flavobacterium psychrophilum. Dietary lauric acid content significantly impacted whole-body lauric acid levels in a dose-dependent manner, with BSFL diets showing higher levels than FM and SBM diets. Fish fed diets with BSFL exhibited enhanced survivability against F. psychrophilum infection compared to SBM-fed fish, with the highest survival rates observed in the WB5 (5% whole-body BSFL) group. Histological analysis demonstrated improved intestinal morphology in BSFL-fed fish, particularly evident in the absence of pathogenic enteritis. Gene expression analysis revealed upregulated proinflammatory markers (IL-8, TNF-a, C5) in BSFL-fed fish post-challenge, indicating an enhanced immune response. These findings indicate the potential of BSFL as a functional feed component to enhance the SBM inclusion in rainbow trout with improved health and performance. By strategically reducing inclusion levels and positioning BSFL as a complement to traditional protein sources, aquafeed formulations can mitigate economic concerns while maximizing the benefits of this sustainable alternative.