Fuente: PubMed "microbial biotechnology" Sci Rep. 2026 Jul 10. doi: 10.1038/s41598-026-57479-1. Online ahead of print.ABSTRACTThe current study evaluated the probiotic potential of Bacillus cereus PKA18, isolated from indigenous Clarias batrachus, as a dietary supplement for the cultivation of Clarias magur fingerlings (In India, the species Clarias batrachus was reclassified as the neotype Clarias magur). Prior to application in fish, Bacillus cereus PKA18 was subjected to safety evaluation, which confirmed negative enterotoxin production, non-hemolytic (γ-hemolysis) behavior on sheep, fish, and human blood agar, and the absence of pathogenic effects or adverse impacts on fish growth following intraperitoneal administration. A total of 240 fingerlings (average weight: 4.96 ± 0.06 g) were randomly assigned to four dietary groups (Control, C1, C2, and C3), each in triplicate, and reared for 60 days in continuous-flow chambers (92 × 61 × 92 cm³; 516 L; 5 cm bottom mud). The control group received basal feed without any probiotic additives, while treatment groups were administered feed supplemented with increasing concentrations of B. cereus PKA18: C1 (2 × 104 CFU), C2 (2 × 105 CFU), and C3 (2 × 106 CFU) per 100 g of feed. Fish in the C2 group exhibited significantly (p < 0.05) superior performance in terms of specific growth rate (3.14 ± 0.05), protein efficiency ratio (2.15 ± 0.12), and live weight gain (27.77 ± 1.24 g), along with the lowest feed conversion ratio (1.29 ± 0.11). Serum biochemical analyses showed notable enhancement in total proteins and reduction in hepatic enzymes (ALT, ALP, AST) in C2-fed fish. Antioxidant enzyme activities were significantly higher in the C2 group. These included superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX). Malondialdehyde (MDA) levels were lowest in this group. Digestive enzyme activities (protease, amylase, cellulase, xylanase, and lipase) were also significantly higher in the C2 group compared to control. Species-level 16 S rRNA gene analysis demonstrated that probiotic-fed Clarias magur exhibited a marked shift in intestinal microbiota, characterized by dominance of beneficial Cetobacterium spp., enrichment of Bacillus spp., and a significant reduction of opportunistic and pathogenic bacteria compared to the control group. Functional profiling further revealed that probiotic supplementation promoted a more metabolically efficient microbial community, with targeted enrichment of core metabolic and genetic information processing pathways despite lower overall functional abundance. Following a pathogenic challenge with Vibrio vulnificus (MTCC 1145), fish in the control and C2 groups were assessed for immune response. Fish fed C2 have demonstrated enhanced activity of respiratory burst, myeloperoxidase, α2-macroglobulin and antiprotease. Additionally, a significant upregulation of immune-related genes (IL-6 and C3a) was observed in the liver, muscle, and intestinal tissues of fish fed with C2. Post-challenge survivability was found to be highest in the C2 group, indicating improved resistance to vibriosis. Overall, the study identifies 2 × 105 CFU/100 g feed of B. cereus PKA18 (C2 feed) as the optimal probiotic dose for promoting growth performance, digestive activity, immune functions and disease resistance in Clarias magur. These findings support its potential application in the conservation-oriented aquaculture of this endangered species.PMID:42431976 | DOI:10.1038/s41598-026-57479-1