Evaluation of processed soy ingredients for largemouth bass (Micropterus nigricans) fingerlings on growth performance, intestinal health, and disease susceptibility

Authors: SEMLA, JAMISON - Auburn University; BUTTS, IAN - Auburn University; DAVIS, D. - Auburn University; OLADIPUPO, ABDULMALIK - Auburn University; Lafrentz, Benjamin; BRUCE, TIMOTHY - Auburn University

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2025
Publication Date: 7/3/2025
Citation: Semla, J.L., Butts, I.A., Davis, D.A., Oladipupo, A.A., Lafrentz, B.R., Bruce, T.J. 2025. Evaluation of processed soy ingredients for largemouth bass (Micropterus nigricans) fingerlings on growth performance, intestinal health, and disease susceptibility. Animal Feed Science and Technology. 327:116432. https://doi.org/10.1016/j.anifeedsci.2025.116432.
DOI: https://doi.org/10.1016/j.anifeedsci.2025.116432

Interpretive Summary: The largemouth bass (Micropterus spp.) is a native sportfish in the United States with a growing interest in becoming a food fish species. Feed is one of the largest expense sectors within the industry, with fishmeal making up a large portion of the cost. Aquaculture is moving towards a more sustainable direction, investigating renewable protein sources such as soy-based ingredients for aquafeed formulations. A feeding trial was conducted to examine growth performance, health metrics, and disease susceptibility in largemouth bass fingerlings fed formulated diets with either soybean meal, enzyme-treated soybean meal, or a soy protein concentrate. After a 14-week culture period, the largemouth bass displayed almost no differences in growth performance, except for the feed conversion ratio. The largemouth bass fed the basal dietary treatment had a lower average feed conversion ratio, compared to the largemouth bass fed a soy-based dietary treatments. Additionally, this study investigated health parameters relating to gut inflammation caused by the antinutrients commonly found in soybean meal. No differences in gut morphology or inflammatory gene expression were detected in the largemouth bass fed either a fishmeal-based diet or when fed a soy-based diet. We also examined gut microbiome across dietary treatments. The results showed no differences in the overall microbial diversity, but the actual composition of the species present varied among the different treatments. Lastly, the largemouth bass were infected with Flavobacterium columnare following the feeding trial period. The results showed no difference in mortalities across all dietary treatments. Overall, this study demonstrated the potential for soy-based ingredients to be used in formulated largemouth bass diets. The experimental inclusions in this trial did not affect growth, health status, or disease susceptibility compared to a basal, fishmeal-based diet. These findings open the door to feed cost reductions for producers and, in turn, may allow for increased profit margins when culturing this species.

Technical Abstract: Largemouth bass is a critically important sportfish in the United States, and cultural practices have led to the potential of this species as a food fish. The aquaculture industry relies heavily on fishmeal (FM) as a source of protein in dietary formulations. Although an excellent protein source, FM is subject to supply shortages, increased demand, and variable pricing. Soy proteins are also considered an excellent protein source but influence growth performance and health in several aquaculture species. To evaluate the potential of soy proteins in largemouth bass diets, a feeding trial was conducted with largemouth bass fingerlings (initial weight; 6.15 ± 0.11g) while formulating dietary treatments using a solvent extracted soybean meal (SBM), soy protein concentrate (SPC), or enzyme-treated soybean meal (ESBM) replacing FM. The study evaluated growth performance, intestines (histological examination, gene expression, and microbiome), health metrics of blood (sera lysozyme and chemistry), and susceptibility to columnaris disease. Endpoint growth results revealed no significant differences in growth parameters, but a difference in feed conversion ratio (P < 0.001). Qualitative histological differences were not found in the thickness of the lamina propria, thickness of connective tissue beneath folds, and vacuolization (P = 0.344). Gene expression of targeted cytokines in the intestine found no differences for il1b, il8, il10, and tgfb (P = 0.429). Gut microbiome differences did not occur for alpha diversity; richness, evenness, or the Shannon index (P = 0.082). However, differences occurred in beta diversity; Bray-Curtis (P = 0.002) and unweighted-UniFrac (P = 0.038). Blood sera differences were found for lysozyme activity, albumin, alkaline phosphate, alanine transaminase, creatine, globulin, and total protein concentrations (P = 0.044). Finally, the largemouth bass were subjected to an in vivo immersion-based challenge with Flavobacterium columnare (isolate ARS-LMB-23-5; 4.98´106 CFU mL-1 exposure). No differences in endpoint CPM were found among dietary treatment-fed largemouth bass (P = 0.530), but a difference in survival (P < 0.001) was discerned via Kaplan-Meier analysis. This study demonstrates the potential of replacing FM with soy proteins in largemouth bass fingerlings while showing comparable growth performance.