Investigation of bacterial gut flora of prussian carp (carassius gibelio (bloch, 1782)) inhabiting hirfanli dam lake

This study aimed to isolate, determine the antagonistic activities and molecular identification of culturable bacteria in the intestinal flora of Carassius gibelio inhabiting Hirfanlı Dam Lake. Intestinal contents of 6 healthy individuals obtained in March 2023 were homogenized in sterile physiological serum and serial dilutions were made. Nutrient agar (NA), Eosin Methylene Blue Agar (EMB), Esculin Bile Agar (EBSA), De Man-Rogosa-Sharpe Agar (MRS) and Bacillus Chromogenic Agar (BCA) were inoculated. High total bacterial loads were detected in the range of 2.5×10⁷–3.5×10⁸ CFU/mL in NA. 44 isolates were purified according to colony morphology; Among these, 6 isolates with antagonistic potential were selected (NK-7, NK-14, NK-36, NK-38, NK-40, NK-42). These isolates were tested for their antagonistic activities against E. coli, K. pneumoniae, S. aureus, E. faecalis, B. subtilis, B. cereus and Candida species using the agar well diffusion method. It was determined that isolates NK-36, NK-38, NK-40 and NK-42 in particular showed antagonistic activity against Gram-positive reference strains, and all isolates showed antagonistic activity against C. albicans and C. tropicalis. Based on 16S rRNA sequencing and phylogenetic dendogram analysis, isolate NK-7 was identified as Pseudomonas putida, isolates NK-14 and NK-36 as Bacillus sp, isolate NK-38 as Enterobacter mori, and isolates NK-40 and NK-42 as Acinetobacter calcoaceticus. The findings suggest that the intestinal flora of C. gibelio has a high microbial load, with members of Proteobacteria and Firmicutes predominating, and that some isolates may exhibit antagonistic activity against pathogens. Recognizing the limitations of the culture-dependent approach (culturable fraction only), the study emphasizes the need for metagenomic validation with bile salt and low pH tolerance, epithelial adherence, safety, and in vivo efficacy tests for the selected isolates to be considered biocontrol/probiotic candidates in aquaculture.