First report of significant growth improvement of Totoaba macdonaldi using Bacillus and soy

Soybean product utilization in carnivorous fish feeding is limited due to the presence of antinutritional factors (ANFs), which can affect fish growth performance and health status. Probiotic bacteria are commonly used to improve feed utilization in animals unable to digest high levels of protein, carbohydrate, and complex lipids from plant origin. In this study, we evaluated Bacillus sp1, sp3, sp4, and 9b strain probiotic capacity in Totoaba macdonaldi juveniles fed with high levels of soy protein concentrate (SPC). In vitro assays showed that sp1 and sp3 strains were capable of degrading soybean products and other plant-based ingredients commonly used in diet formulation. Soybean meal semi-solid-state-fermentation (SSSF) showed glycinin and β-conglycinin allergenic proteins, and other antinutritional factors were degraded when sp1 and sp3 strains were added to the SSSF process. HPLC product characterization of soybean meal fermented samples with Bacillus strains showed hydrophilic peptide increment and hydrophobic proteins decrement. Diets containing 30% fishmeal substitution with SPC and Bacillus strains sp1, sp3, sp4, and 9b were formulated and used to feed T. macdonaldi juveniles for 8 weeks. Fish growth was carried out using commercial diet (Ct), experimental diet with SPC and without Bacillus (C30), and experimental diets with SPC and Bacillus strains (C30sp1, C30sp3, C30sp4, C309b). Results show that C30sp1 diet produced better weight gain (WG: 224.56 ± 10.79%) than C30sp3 (196.56 ± 11.38%), C30sp4 (177.08 ± 10.79%), and C309b (190.78 ± 13.22%) diets. C30sp1 also produced better weight gain than Ct commercial (123.08 ± 10.98%) and C30 experimental control (194.90 ± 12.33%) diets. Specific growth rate (SGR), thermal growth coefficient (TGC), feed conversion ratio (FCR), and daily feed intake (DFI) parameters were also improved when C30sp1 diet was used. In conclusion, the ability of the Bacillus sp1 strain to degrade soy protein makes it a great feed additive for T. macdonaldi, enhancing growth performance and resulting in larger fish compared to commercially available feeds.