Isolation, probiotic screening, molecular identification, and dietary evaluation of intestinal Bacillus cereus (LSPNCOF_P1) and its effects on growth performance, hematological, immunological, and carcass characteristics of Cirrhinus mrigala fingerlings

Abstract

Probiotics have gained increasing attention as sustainable approaches for improving fish health and reducing reliance on antibiotics. This study aimed to isolate, characterize, and evaluate the probiotic potential of intestinal bacteria from Cirrhinus mrigala, with a focus on their effects on growth performance, hematological, immunological, and carcass characteristics. Fourteen bacterial isolates were obtained from the intestinal tract and screened for probiotic traits. Based on superior tolerance, isolate C8 (renamed LSPNCOF_P1) was selected and identified as Bacillus cereus through 16S rRNA gene sequencing. A feeding trial was conducted using three dietary inclusion levels (105, 108, and 1010 CFU   mL–1) along with a control group. Growth parameters showed no significant differences among treatments; however, fish fed the diet sprayed with B. cereus at 108 CFU mL–1 showed numerically better weight gain, specific growth rate, and feed conversion efficiency. Hematological parameters, including RBC, Hb, and Hct, were significantly enhanced (p < 0.05) in probiotic-fed groups, while WBC counts decreased, indicating reduced stress and improved physiological status. Immunological responses, including NBT, lysozyme, and MPO activities, were significantly elevated (p < 0.05), particularly in fish fed the diet sprayed with B. cereus at 108 CFU mL–1, reflecting enhanced innate immunity. Carcass composition analysis revealed increased protein content and reduced lipid levels in probiotic-fed fish. Dietary administration of B. cereus, sprayed onto the feed at 108 CFU mL–1, improved health status, immune response, and flesh quality of C. mrigala fingerlings. The findings highlight the potential of host-associated probiotics as sustainable alternatives to antibiotics in aquaculture systems.