Research Highlights

Largemouth Bass Do Well on Soy-Based Diets

By Sarah Hill

Interest in largemouth bass as a food fish species has been growing in the Midwest and Southern U.S., and an Auburn University researcher has been studying feeding those largemouth bass a soy-based diet. China has historically produced large quantities of largemouth bass for food, while the U.S. has primarily focused on the species as a recreational sport fish, says Timothy Bruce, assistant professor, Aquatic Animal Health, Auburn University. Largemouth bass has tremendous potential as a food product.

“Advancing technologies in aquaculture, such as recirculating aquaculture systems, have allowed for better culture methods and control for largemouth bass production,” he says. 

Bruce’s team, including researchers Ian Butts and Allen Davis, conducted a growth study on largemouth bass, replacing fishmeal in the diet with soy at 30%. Three different soy sources were evaluated: soybean meal, soy protein concentrate and fermented soybean meal. After a 14-week study, no differences were found in primary growth metrics for the fish fed different types of soy, although the control diet had a slightly better feed conversion ratio numerically. 

Looking at the distal intestine using histology, the team found that the soybean meal-based diet increased the thickness of the mucosal folds and the inner lamina propria. Thicker and shortened folds make it more difficult for the fish to absorb nutrients from its food, and this can be caused by antinutritional factors present in soybean meal. The fish fed fermented soy and soy protein concentrate diets showed slight changes in their gut, but only one parameter, the height of the mucosae, was different from that of the control group.

Protection Against Columnaris Disease

The largemouth bass industry has been impacted by bacterial pathogens such as Flavobacterium spp., according to Bruce, which cause columnaris disease in the fish. Bruce’s team exposed the largemouth bass to columnaris-causing bacteria to see if soy-based diets influenced fish survival. The team speculates that largemouth bass with enhanced growth or overall improved well-being from soy-based diets will have decreased susceptibility to columnaris disease and reduced mortality.

“Producers with columnaris diseases have seen high mortality rates,” Bruce says. “In our challenge trial, we saw very low mortality rates, but we have yet to see any major dietary influence on the disease.”

Bruce’s team plans to conduct more studies on largemouth bass this summer, evaluating short-term performance on soy-based diets with revised formulations. The team will also run additional columnaris disease challenges and look at potential gene expression changes due to gut inflammation.

Published: Aug 19, 2024