Effects of Dietary Protease at Different Levels of Probiotics on the Growth Potential, Enzyme Activities, Physiological and Hematoimmune Responses of Striped Catfish (Pangasianodon hypophthalmus (Sauvage, 1878))

Probiotics and exogenous enzymes play essential roles in the growth and health of aquatic animals. This study explored the interactive effects of probiotics (Prob) and exogenous protease (Prot) on the growth indices, digestive and antioxidant enzyme activities, body composition, hematoimmune parameters and serum biochemical indices of striped catfish (n = 600, ≈10.17 ± 0.03 g). In this context, ten diets were formulated with a crude protein level of 35.23% by incorporating Prob (0.0, 1.0, 2.0, 3.0, and 4.0 g/kg) at each Prot level (0.5 and 1.0 g/kg). After a 14-day acclimatization period, the fish were stocked in ten groups, each in triplicate (20 fish/aquaria (40 × 40 × 70 cm, i.e., width × depth × length)) in a 2 × 5 factorial design and fed for 90 days at 3% of their body weight. The results of the current study revealed significant improvements in growth performance with Prob supplementation at both Prot levels (0.5 and 1.0 g/kg). At 0.5 g/kg Prot, FBW and AWG increased with increasing Prob supplementation, reaching their highest mean values at 4.0 g/kg Prob. However, WG% was highest (498.49%), and FCR was lowest (1.33) at 2.0 g/kg Prob, with no substantial further improvement at higher Prob levels. In contrast, at 1.0 g/kg Prot, the optimal Prob level shifted to 1.0 g/kg, resulting in a WG% of 486.99% and an FCR of 1.37. Similarly, the main effect and interactive effect were significant for digestive and antioxidant enzymes in response to dietary Prot and Prob. However, the levels of malondialdehyde (MDA), white blood cells (WBCs), and liver enzymes significantly decreased, reversing the growth trend. Furthermore, hematoimmunological parameters, including red blood cell (RBC) count, hemoglobin (Hb) concentration, hematocrit (HCT), lysozyme activity, and immunoglobulin M (IgM), showed the highest mean values at 4.0 g/kg Prob with 0.5 g/kg Prot, although the differences among the 2.0, 3.0, and 4.0 g/kg Prob treatments were not statistically significant. At 1.0 g/kg Prot, these parameters generally showed the highest mean values at 1.0–2.0 g/kg Prob. Moreover, the proximate analysis (crude protein, crude fat, moisture and ash) was not significantly (p > 0.05) affected by either supplement. The polynomial broken-line regression analysis based on WG% indicated that the optimum Prob level with 0.5 g/kg protease was 1.46 g/kg, whereas at 1.0 g/kg protease supplementation, the optimal probiotic level was estimated at 1.39 g/kg. In conclusion, dietary supplementation with Prob and Prot enhances the growth and health status of P. hypophthalmus, suggesting a sustainable and economical approach for intensive catfish farming.