Effects of Dietary Phenylalanine: Tyrosine Ratio on Growth, DNA/RNA, Serum Biochemistry, Digestive Enzyme Activities and Physiological Responses of Heteropneustes fossilis

Stinging catfish (Heteropneustes fossilis) has high consumer demand due to its high iron and calcium contents. Also, being a lean fish, it is very suitable for people who do not prefer to consume animal fats. In view of its nutritional and therapeutic significance and lack of data on dietary phenylalanine: tyrosine ratio, a dose-response experiment was conducted to determine phe: tyr ratio for H. fossilis fry (4.1±0.3g). Six isonitrogenous (380 g/kg crude protein) and isocaloric (15.3 kJ/g digestible energy) amino acid test diets were prepared by adjusting 26.6 g/kg of total phenylalanine and tyrosine in varying ratios of phenylalanine/tyrosine (30:70, 40:60, 50:50, 60:40, 70:30, 80:20) on molar basis. Quadruplicate groups of fishes were fed with diets indicated for 12-weeks to apparent satiation, thrice daily. Mathematical analyses of Daily Growth Coefficient (DGC%), Specific Growth Rate (SGR%/day), Feed Conversion Ratio (FCR) and Erythrocyte Osmotic Fragility (EOF) as quadratic-broken line regression analyses, exhibited optimum dietary phenylalanine: tyrosine ratio of 64.94: 35.06 corresponding to 15.83 g/kg: 8.55 g/kg on equimolar basis. Data of this study would be of high significance to ensure that optimum phenylalanine and tyrosine ratio of fish is met while using a greater variety of cost-effective dietary protein feedstuffs for sustainable aquafarming of this fish.