Effects of dietary fermented soybean meal with Thua nao starter on the growth performance, body composition, and disease resistance against Aeromonas hydrophila of Nile tilapia ( Oreochromis niloticus )

The purpose of this study was to evaluate the improvement of the nutritional value of soybean meal by using Thua nao starter as a dietary supplement for tilapia culture. The study covered five different experimental diets, each containing fermented soybean meal (FSBM): FSBM0 (0 g/kg), FSBM75 (75 g/kg), FSBM150 (150 g/kg), FSBM225 (225 g/kg), and FSBM300 (300 g/kg) for 10 weeks. The results of the fermentation process revealed that the FSBM exhibited an abundance of Bacillus and Kosakonia, along with notable enzyme activities such as protease, filter paper cellulase, and carboxymethyl cellulase. Furthermore, the protein content of the FSBM increased from 42% to 44%. When the tilapia feed was supplemented with the FSBM, it was observed that supplementation with amounts below FSBM225 had no significant impact on fish growth. Conversely, the diet of FSBM300 had a detrimental effect on growth. Fish receiving FSBM diets demonstrated elevated white blood cells, particularly in those fed FSBM150, FSBM225, and FSBM300, with an increase in neutrophils in the FSBM225 and FSBM300. The whole-body composition revealed no significant changes in crude protein and ash, but there was reduction in crude lipid content. Notably, the supplementation of FSBM had a positive impact on the disease resistance of tilapia to Aeromonas hydrophila, with the FSBM225 group showing the lowest fish mortality rate at 23.8%. These findings indicate that the inclusion of FSBM at a concentration of 225 g/kg in the fish diet does not negatively affect growth and improves survival rates when exposed to A. hydrophila. This indicates that FSBM can be considered a valuable dietary supplement to resist bacterial infection for tilapia farming.