Effect of dietary taurine/ methionine ratios on growth performance, digestive, metabolic enzyme activity, antioxidant status and innate immune responses in pangasius (Pangasianodon hypophthalmus)

The study aimed to evaluate the effect of dietary taurine and methionine ratios on growth performance, digestive enzyme activity, metabolic enzyme activity, antioxidant status and innate immune responses in pangasius fingerlings when fed with plant ingredients. Four isonitrogenous (300 g/kg crude protein) and isolipidic (60 g/kg crude lipid) diet with varying ratios of Tau (g/kg)/Met (g/kg) (T0/M25, T5/M20, T10/M15, and T15/M10) were prepared. Pangasius (Pangasianodon hypophthalmus) fingerlings were randomly stocked in twelve 150 L FRP tanks with 20 fingerlings (6.43 ± 0.06 g) in each and fed experimental diets for 60 days. Final weight, weight gain, specific growth rate and protein efficiency ratio were significantly higher (P < 0.001) in T15/M10 group and the same group showed lower feed conversion ratio. The whole-body crude protein and ash showed a positive linear and quadratic response (P < 0.001) and was highest in T15/M10 group. Likewise, the same group showed lowest crude lipid and moisture and exhibited negative linear and quadratic responses. Serum glucose and triglycerides were also significantly lower (P < 0.05) in T15/M10 group. The protease, amylase and lipase had a positive linear and quadratic response (P < 0.001) and were significantly higher (P < 0.05) in T15/M10 group. Metabolic enzymes viz. aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase, glucose 6 phosphate dehydrogenase, hexokinase, and fructose 1,6 bisphosphate showed significantly higher (P < 0.05) activity in T15/M10 diet and except for glutamate dehydrogenase which has no apparent effect. The antioxidant enzyme activity such as superoxide dismutase, catalase, glutathione S-transferase and glutathione peroxide showed a positive linear and quadratic (P < 0.05) response to different Tau/Met ratio. Lipid peroxidation activity showed negative linear and quadratic responses (P < 0.001) and was significantly lower (P < 0.05) in T15/M10 group. Respiratory burst activity and lysozyme activity showed a positive linear and quadratic response (P < 0.001) and were significantly higher (P < 0.05) in T15/M10 group. The expression level of proinflammatory gene, Interleukin-1β did not show any significant difference among the treatments (P > 0.05). The transferrin gene expression was upregulated in T15/M10 group. In summary, the growth performance was increased when the taurine in the diet increased, whereas the only methionine diet ceased the growth performance. It seems that methionine is not as efficient as supplementing intact dietary taurine. The T15/M10 diet showed to be the best inclusion for pangasius in a plant-based diet.