An 8-week feeding trial with juvenile largemouth bass was initiated in Oct. 2023. We tested nine diets designed to meet all known nutrient requirements of largemouth bass. The control diet contained 15% fish meal. The other diets contained no fish meal but similar amounts of other animal proteins (poultry and blood meals). The experimental variables included conventional soybean meal (48% protein, dehulled, solvent-extracted), fermented soybean meal (Pepsoygen ™), a palatant (spray-dried poultry powder at 1%) and a prebiotic (Hilyses™ at 0.5%). Diets with conventional or fermented soybean meal, with or without the palatant, prebiotic or both were tested against the control diet. Groups of 20 fish (average 4.1 g) were stocked in each of 5 replicate tanks per diet (9 diets, 45 tanks total). Fish were fed twice daily to satiation for 8 weeks. Final weights and counts were taken and tissues were preserved for analysis.
Overall, results from this project indicated that there were no clear advantages of using fermented soy over conventional 48% protein, dehulled, solvent-extracted soybean meal in terms of weight gain, survival, feed intake or feed conversion ratio (FCR). The conventional soy would be cheaper, which would enhance cost-effectiveness of diets. There were a number of soy diets that supported similar weight gain, survival, feed intake and FCR to the control diet (with fish meal). Interestingly, the palatant did not improve feed intake, which differs from results with other fish species. The prebiotic appeared to suppress feed intake slightly for unknown reasons. However, the prebiotic also improved FCR, which means the fish ate less but converted the diet more efficiently. This finding could also have economic significance because the cost of the prebiotic might be offset by supporting good growth and nutrient utilization with less feed. Additional analyses are still in progress (e.g., gut microflora analysis).