The efficacy of dietary commercial probiotic (Bacillus subtilis) on growth performance, hemato-biochemical response, and histological status of red tilapia (Oreochromis sp.)

Red tilapia (Oreochromis mossambicus x O. niloticus) is a target fish in aquaculture. One of the recent topics is improving its feed quality. Bacillus sp. is a common aquaculture probiotic that emits several exoenzymes and can stimulate fish performance. In the current study, red tilapia (5.1 +/- 1.1 g) were fed on a control diet (30% crude protein and 7.74% ether extract) enriched with a commercial probiotic, B. subtilis of 0, 2, 3, and 4 g/kg feed (expressed as BS0, BS1, BS2, and BS3, respectively) until satiation three times daily for 70 days. B. subtilis positively (p < 0.05) modulated the fish growth performance and hematological profile, especially at BS2 and BS3. The polynomial regression curves indicate that the BS3 displayed the optimum growth performance compared with other treatments. Regarding the biochemical indices, feeding fish on the BS3 significantly (p < .05) reduced levels of glucose (mg/dL), aspartate transferases (U/L), and alanine transferases (U/L), as well as alkaline phosphatase (U/L), while increasing total protein (g/dL), albumin (g/L), and globulin (g/L) levels. Adding B. subtilis to diets for red tilapia did not affect their proximate chemical composition. Histologically, intestinal sections showed improved muscular layers, intestinal villi, and absorption zones due to the B. subtilis supplementation, particularly at the BS3. With increasing B. subtilis doses in diets, especially at BS3, the liver sections showed considerable modulation in the structure of hepatocytes surrounding the central hepatic veins, blood sinusoids, and pancreatic glands (surrounding the portal hepatic vein). In conclusion, feeding red tilapia on diets enriched with commercial probiotic B. subtilis at rates of 4 g/kg feed (BS3) enhanced their overall health status and growth performance.