Effect of glycine supplementation on growth performance, body composition and salinity stress of juvenile Pacific white shrimp, Litopenaeus vannamei fed low fishmeal diet

An 8-week feeding trial was conducted to evaluate the optimum dietary glycine level in low fishmeal diet for juvenile Pacific white shrimp, Litopenaeus vannamei. Six practical diets (44.4% protein, 8.8% lipid) were formulated to contain graded levels (2.26, 2.33, 2.44, 2.58, 2.67 and 2.74%) of l-glycine. Each diet was randomly assigned to triplicate groups of 30 shrimps (approximately 0.61 g) and the shrimps were fed 4 times a day to apparent satiation. The results indicated that the weight gain and specific growth rate were significantly increased with the supplementation of glycine. The highest weight gain and specific growth rate were observed at 2.56% dietary glycine, and then decrease with a further increase in dietary glycine. Hepatosomatic index, protein productive value and condition factor were also significantly influenced by the dietary glycine levels and show a similar trend to those of growth performance. There were no significant differences observed in feed efficiency, protein efficiency ratio and survival among all treatments. Mg, Ca and Fe concentrations in whole body were significantly increased with the supplementation of glycine. Non-essential amino acid, essential amino acid and arginine ratio in muscle were significantly affected by the dietary glycine levels. Dietary glycine levels higher than 2.44% significantly increased the survival of shrimps after 2 h and 3 h of acute salinity change, and T-SOD activity and Na+/K+-ATPase activity in hematological and hepatopancreas before and after acute salinity change are also significantly affected by the dietary glycine levels. Analysis by second-order regression of weight gain indicated that the optimal dietary glycine level was 2.54% of the dry diet (5.7% of the dietary protein and 6.66% of the dietary amino acids).