Complementing the high soybean meal diet with black soldier fly larvae meal as a functional feed ingredient to improve the performance, nutrient profile, and gut health of rainbow trout, Oncorhynchus mykiss

Authors: SINGHA, KRISHNA - University Of Idaho; ABANIKANNADA, MOSOPE - University Of Idaho; MA, JIE - US Department Of Agriculture (USDA); Romano, Nicholas; KOUTSOS, ELIZABETH - Enviroflight Llc; ADAMS, DANIEL - Enviroflight Llc; KUMAR, VIKAS - University Of Idaho

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2025
Publication Date: 3/8/2025
Citation: Singha, K.P., Abanikannada, M.F., Ma, J., Romano, N.P., Koutsos, E., Adams, D., Kumar, V. 2025. Complementing the high soybean meal diet with black soldier fly larvae meal as a functional feed ingredient to improve the performance, nutrient profile, and gut health of rainbow trout, Oncorhynchus mykiss. Aquaculture. 603:742405. https://doi.org/10.1016/j.aquaculture.2025.742405.
DOI: https://doi.org/10.1016/j.aquaculture.2025.742405

Interpretive Summary: The most commonly used alternative protein source to fishmeal is soybean meal (SBM), which is cheaper, more readily available and sustainable. However, rainbow trout, like other carnivorous marine fish, suffer from intestinal enteritis when fed high amounts of SBM in their diets. This is due to various antinutritional factors within SBM that irritate the intestine which disrupts nutrient absorption and decreases their overall health. A promising solution is the use of “functional feed ingredients” that can mitigate SBM induced intestinal enteritis in carnivorous fish. Black soldier fly larvae (BSFL) has the potential to act as a functional ingredient, but it is unclear whether this is influenced by the high amount of fat with BSFL. The dominant fat in BSFL is saturated fatty acid that is mostly in the form of lauric acid. In this study, rainbow trout were fed high SBM diets with whole body (WB) BSFL or defatted (DB) BSFL at two different levels of 2.5 or 5%. The two control diets were fishmeal based or SBM based with no BSFL. Diet with 5% of WB led to be better rainbow trout growth than the other SBM diets as well as reduced intestinal inflammation. Additionally, there was evidence that BSFL improved mineral absorption. This study indicates that BSFL meal (not defatted) can enhance rainbow trout growth by substantially reducing the negative effects of dietary SBM. While BSFL is still an expensive ingredient, relatively small amounts can improve the utilization of SBM in rainbow trout as a functional feed ingredient. Further studies like this on other carnivorous fish may be worthwhile.

Technical Abstract: This study explores the use of black soldier fly larvae (BSFL) as a "functional feed ingredient" in aquafeed formulations, aiming to mitigate the adverse effects of high soybean meal (SBM) inclusion in the diet of rainbow trout. Two forms of BSFL, whole body (WB) and defatted (DB), were supplemented at different levels (2.5% and 5%) in a high SBM diet. Six isonitrogenous (crude protein 50%) and isolipidic (20%) diets include fishmeal-based diet (FM), high SBM (SBM), WB at 2.5 and 5% (WB2.5 and WB5), and DB at 2.5 and 5% (DB2.5 and DB5). Fish (5.2 g) were randomly distributed in twenty-four tanks (30 fish/tank), maintaining four replications for each diet, and fed six experimental diets at apparent satiation for 10 weeks. The research investigated the impact of BSFL supplementation on growth, feed utilization, proximate and nutrient (amino acids, fatty acids, and minerals) compositions, immune-related gene expression, and intestinal histopathology. The results indicated that a 5% inclusion of whole-body BSFL (WB5) in the diet outperforms all other dietary treatments regarding growth. Fatty acid composition analysis shows higher levels of lauric acid in BSFL-supplemented groups, notably in WB5. Mineral composition analysis suggests that BSFL supplementation, especially WB5, can restore levels of sulfur and zinc affected by high SBM inclusion. Histopathological analysis of the intestine demonstrates that whole-body BSFL supplementation, particularly at 5% level, reduces inflammation and mucous cell populations, enhancing intestinal health. Gene expression analysis indicates a higher level of the complement factor 5 (C5) gene in the BSFL-supplemented group (DB5), suggesting an increase in the activity of the complement system, while the expression of IL8 and TNF did not show any difference. Overall, this study demonstrates the potential of BSFL as a functional feed ingredient to enhance rainbow trout performance and gut health in high SBM diets.