EFFECTS OF TRYPTOPHAN SUPPLEMENTED IN LOW PROTEIN DIETS ON APPARENT DIGESTIBILITY COEFFICIENTS, DIGESTIVE ENZYME ACTIVITY AND AMINO ACIDS COMPOSITION OF LITOPENAEUS VANNAMEI

To examine effects of L-tryptophan supplemented in low protein diets on apparent digestibility coefficients, digestive enzyme activity and amino acids composition of the whole body in Litopenaeus.vannamei, six diets including high protein diet with 40.79% crude protein (HT0), and low protein diets with 37.01% crude protein supplemented with 0 (LT0), 1.20 (LT1), 2.50 (LT2), 5.0 (LT3) and 10.0 (LT4) g/kg L-tryptophan were formulated to feed 960 shrimp with the average body weight of (2.000.01) g that were randomly allocated into 6 groups with 4 replicates for a 56-day experiment. The results showed that tryptophan supplemented in low protein diets significantly increased the apparent digestibility coefficients (ADCs) of crude protein (CP) and amino acids, dry matter (DM), gross energy (GE), protease activity, and the body amino acids composition (P0.05). The ADCs of CP in LT3 and LT4 were significantly higher than that of LT0 (P0.05). The ADCs of methionine in LT3 was significantly higher than that of LT0 (P0.05). The ADCs of tyrosine in LT3 was significantly higher than that of HT0 (P0.05). The ADCs of DM in LT3 and LT4 were significantly higher than that of LT0 (P0.05). The ADCs of GE in LT1, LT2, LT3 and LT4 were higher than that of LT0, and the ADCs of GE in LT4 significantly higher than that of LT0 (P0.05). The addition of L-tryptophan significantly increased the intestine protease activity, and LT2 was the highest group. The hepatopancreas protease activity in LT2, LT3 and LT4 were significantly higher than that of LT0 (P0.05), but there was no significant difference compared to HT0 (P0.05). Aspartic acid, glycin, alanine, methionine and leucine content of the shrimp in LT4 was significantly higher than that of LT0 (P0.05), and lysine content of the shrimp in LT2 were significantly higher than that of LT1 (P0.05). In conclusion, L-tryptophan supplemented in low protein diets could enhance the ADCs of CP, amino acids, DM, GE, the protease activity, as well as improve the shrimp body amino acids composition.