International Journal of Aquaculture, 2026, Vol.16, No.4, 234-242 http://www.aquapublisher.com/index.php/ija 236 2.7 Molecular identification Genomic DNA was extracted and amplified using universal 16S rRNA primers. PCR products were sequenced and analyzed using BLAST analysis. Genomic DNA was extracted using a modified CTAB protocol according to Saraniya and Jeevaratnam (2012). 2.8 Statistical analysis All experiments were conducted in triplicate and data were expressed as mean ± standard deviation (SD). Statistical analyses were performed using one-way analysis of variance (ANOVA) to determine significant differences among treatments. When significant differences were detected (p < 0.05), means were separated using Duncan’s Multiple Range Test (DMRT). Superscript letters were used to denote statistical differences between treatments. For microbial enumeration data, bacterial counts were log₁₀ transformed prior to analysis to ensure normal distribution and homogeneity of variance. The statistical model applied was Yij=μ+Ti+ϵij Where: 1 Yij= observed value 2 μ= overall mean 3 Ti= treatment effect 4 ϵij= experimental error Significance was declared at p < 0.05. All analyses were conducted using SPSS version 25.0 (IBM Corp., USA). 3 Results 3.1 Distribution of gut microbiota The distribution of bacterial populations along the intestinal tract of Oreochromis niloticus is presented (Figure 1). The results indicate that the lower gut harboured consistently higher bacterial loads compared to the upper gut across all bacterial groups, including total heterotrophic bacteria, cocci, and Bacillus spp. This pattern may be associated with the more stable physicochemical conditions and nutrient availability in the distal intestine, which favor microbial proliferation and colonization. Table 1 Relative abundance of bacterial groups in the gastrointestinal tract Bacterial Group Representative Genera Upper Gut (CFU g⁻¹) Lower Gut (CFU g⁻¹) Probiotic Potential Helicobacter / Fusobacterium Opportunistic commensals 1.75 × 10¹ᵃ 6.65 × 10⁶ᵇ No Cocci bacteria Staphylococcus, Streptococcus 1.14 × 10⁶ᵃ 3.05 × 10⁶ᵇ Variable Bacillus spp. Spore-forming rods 1.14 × 10⁶ᵃ 3.05 × 10⁶ᵇ Yes Different superscripts indicate significant differences (p < 0.05). 3.2 Morphological and biochemical characterization 3.2.1 Gram staining Gram staining result presented shows both Bacillus spp. and Cocci bacteria to be gram positive while Helicobacter spp and Fusobacterium spp to be gram negative (Table 2). 3.2.2 Spore test Table 3 shows that only Bacillus spp. is capable of sporulation, while the other isolates; Cocci bacteria, Helicobacter spp. and Fusobacterium spp. are non-spore forming bacteria.
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