Effect of dietary protein and energy levels on growth, oxygen consumption,haemolymph and digestive gland carbohydrates, nitrogen excretion and osmotic pressure of Litopenaeus vannamei (Boone) and L-setiferus (Linne) juveniles (Crustacea, Decapoda; Penaeidae)

The influence of protein and energy levels on growth rate, survival. pre- a nd post-prandial oxygen consumption. ammonia excretion, haemolymph glucose (HG), glycogen in digestive gland and osmotic pressure (OP) in white shrimp Litopenaeus vannnmei (Boone) and L. setiferus (Linne) juveniles was studie d. Diets containing a high-quality protein at a protein/energy (P/E) ratio of 16, 26, 31 and 36 mg kJ(-1) were fed at 20% of shrimp body weight of two sizes: < 1 g and > 1 g. Both species showed a optimum P/E ratio of 36 mg k J(-1) (33-44% protein and 6-23% carbohydrate) in juveniles <1g. For shrimp >1g, L. setiferus showed a higher growth rate in the diet with 16 mg kJ(-1) (27% protein: 32% carbohydrate) and L. vannamei between 26 and 36 mg kJ(-1 ) (33-44% protein and 6-23% carbohydrate). In both experiments, the growth rate of L. vannamei was 2-3 times that observed in L. setiferus. Routine ox ygen consumption and apparent heat increment (AHI) of L. setiferus juvenile s was two times higher than that observed in L. vannamei juveniles, which c ould indicate that L, setiferus has a higher metabolic rate. The O/N ratio varied according to protein level, with higher values (O/N = 180) with a 16 -mg kJ(-1) diet and lower values (O/N = 73) with a 36-mg kJ(-1) diet in L. setiferus juveniles. A similar variation in O/N ratio was obtained in L. va nnnmei fed with all diets with an interval between 22 and 50. An inverse re lation between ammonia excretion and HG, and digestive gland glycogen (DGG) in relation to an increase in the P/E ratio indicate that both shrimp spec ies are well adapted to use carbohydrates and/or proteins from their diet. The higher values of hyper-osmotic capacity (hyper-OC) were observed in L. setiferus <1g fed with 36 mg kJ(-1) and the lowest in L. vannamei <1 g fed with 31 mg kJ(-1). Intermediate values of hyper-OC were observed in both sp ecies fed all diets indicating that osmotic factors of juveniles <1g of bot h species are more affected by the P/E ratio than juveniles >1g. All result s showed that juveniles > 1 g of both species are less dependent of P/E rat io than juveniles <1 g. Litopenaeus vannnmei is a most tolerant shrimp spec ies with a high capacity to use a wide range of dietary P/E ratios for grow th, which may be due to its lower energy requirements. Litopenaeus setiferu s showed a lower capacity to accept different P/E ratios but the optimum P/ E ratio obtained with this species shows that L. setiferus accept diets wit h a high carbohydrate level as well. These results demonstrate that there a re nutritional and physiological differences that explain the differences t hat have been observed when both species were cultured in commercial ponds.