International Journal of Aquaculture, 2026, Vol.16, No.4, 234-242 http://www.aquapublisher.com/index.php/ija 237 Figure 1 Comparative bacterial load in the intestinal tract of Oreochromis niloticus Image caption: (A) Total heterotrophic bacteria, (B) cocci bacteria, and (C) Bacillus spp. counts in the upper and lower gut segments. Bacterial abundance is expressed as colony-forming units per millilitre (CFU mL⁻¹). The lower gut consistently exhibited higher bacterial populations than the upper gut. Table 2 Gram staining results Isolate Morphology Gram Reaction Bacillus spp. Rod-shaped cells Gram positive Cocci bacteria Spherical cells Gram positive Helicobacter spp. Spiral rods Gram negative Fusobacterium spp. Spindle rods Gram negative Table 3 Spore staining Isolate Spore Formation Bacillus spp. Positive Cocci bacteria Negative Helicobacter spp. Negative Fusobacterium spp. Negative 3.2.3 Catalase and hemolysis test The result of production of catalase and hemolytic test by the Isolates is presented in Table 4. Gas production from the isolates comes out positive for both Cocci and Bacillus spp., while both isolates were negative to hemolysis which is a good sign of potential probiotics Table 4 Catalase and Hemolysis Test Isolate Catalase Hemolysis Bacillus spp. Positive Negative Cocci bacteria Positive Negative The absence of hemolytic activity suggests the isolates are non-pathogenic and safe for probiotic application. 3.3 Acid and bile salt tolerance The results of acid tolerance and bile salt tolerance are presented in Tables 5 and 6, respectively. The results shows that selected isolates survived bile salt at all concentration, however, the tolerance of Bacillus spp. is greater than Cocci bacteria at all level of bile salt concentration. Also, isolates survived pH tolerance at all concentration, meanwhile, the tolerance level of Bacillus spp. at all pH concentration is higher in value than the value recorded for Cocci bacteria.
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