Abstract:A 10-week feeding trial was conducted to study the effects of soybean meal supplemented replacement by peanut meal supplemented with lysine and methionine on growth, apparent digestibility coefficient (ADC) and body composition of juvenile hybrid tilapia (Oreochromis niloticus×O. aureus) at initial mean body weight of 7.30±0.12 g, which were stocked in floating net cages suspended in an earthen pond. Five isonitrogenous and isoenergetic experiment diets (D1~D5) were formulated with low fish meal content (2%). D1 was used as control containing 30% soybean meal (SBM). D2 was formulated with peanut meal (PNM) replacing 50% SBM protein. D3~D5 were formulated on the basis of D2 supplemented with crystalline lysine (0.25%)+methionine (0.05%), microencapsulated lysine (0.25%) + methionine (0.05%) or microencapsulated lysine (0.50%)+methionine (0.10%), respectively. Chromic oxide (0.5%) was added as an external indicator to determine the ADC for nutrient or energy of the experimental diets. The results showed that no significant difference (P>0.05) were found among survival rates of the experimental diets. Specific growth rate (SGR) had no significant differences (P>0.05) between the control and D5, which were significantly higher (P<0.05) than the other three diets, and D2 resulted in the lowest SGR. Fish fed D2 and D3 had significantly higher (P<0.05) feed conversion ratio than D5 and the control. Fish fed D5 and the control had significantly higher (P<0.05) protein efficiency ratio than D2 and D3. Condition factor showed no significant difference (P>0.05) among the D4, D5 and the control, which were significantly higher than D2 and D3 (P<0.05). There were no significant differences (P>0.05) in viscerasomatic index and hepato-somatic index between the experimental diets. ADCs of dry matter, crude lipid, gross energy and essential amino acid had no significant difference (P>0.05) among the experimental diets. ADC of crude protein had no significant difference (P>0.05) among the microencapsulated amino acid supplemented diets and the control, however, which were significantly higher (P<0.05) than D2. Whole-body proximate and essential amino acid composition of the fish were not affected by replacement of SBM with PNM or supplement of crystalline or microencapsulated lysine and methionine. Compared to crystalline amino acid, the results indicated that dietary microencapsulated lysine and methionine supplements obviously improved the growth performance of juvenile tilapia and the ADC of dietary protein under the conditions of this experiment.
