Amino Acid Digestibility of Catfish (Clarias gariepinus) Fed Soyabean Meal Supplemented with Lysine and DL-Methionine

Background and Objective: Soyabean Meal (SBM) could be a suitable replacement for the expensive fishmeal but for its low digestibility in fish. Appropriate dietary supplements of amino acid can improve digestibility of SBM based diets. Therefore, the effect of supplementing lysine and DL-methionine in solvent extracted soyabean based diets (SESBD) on performance and amino acid digestibility of Clarias gariepinus ( C. gariepinus ) was assessed. Materials and Methods: Juvenile fish (n = 360) with the weight of 17.74±0.29 g were fed experimental diet to satiation for 12 weeks. Six diets containing varied combinations of lysine+DL-methionine (g 100 g ^–1 ) in SESBD were formulated, S ₁ (without supplemental lysine and DL-methionine), S ₂ (0+1 g), S ₃ (0.25+0.75 g), S ₄ (0.5+0.5 g), S ₅ (0.75+0.25 g), S ₆ (1+0 g). Each treatment was in triplicate. Results: Fish fed S ₁ (43.35±4.03 g), S ₃ (40.80±1.74 g) and S ₅ (36.70±5.11 g) were not significantly different (p>0.05) but significantly higher (p<0.05) than those on S ₂ (34.77±1.17). Lysine and DL-methionine supplementation had no significant effect (p>0.05) on feed conversion ratio. Supplemental lysine and methionine resulted in an increase (p<0.05) in both apparent (96.34±0.31) and true (96.51±0.31) protein digestibility in diet S ₅ . The C. gariepinus on S ₅ (95.75±0.26) had a significantly higher (p<0.05) apparent lysine digestibility than other treatments. The optimum estimates of supplemental lysine and methionine in SESBD for the weight gain of C. gariepinus occurred at 0.6 g 100 g ^–1 (R ² = 0.66) and 0.4 g 100 g ^–1 (R ² = 0.42), respectively. Conclusion: The findings suggest that lysine and DL-methionine supplementation could improve growth performance and amino acid digestibility in C. gariepinus fed SESBD.