Influence of dietary carbohydrate on the metabolism of juvenile Litopenaeus stylirostris.

The effect of dietary carbohydrates (CBH) on glucose and glycogen, digestive enzymes, ammonia excretion and osmotic pressure and osmotic capacity of Litopenaeus stylirostris juveniles was studied. The increase of CBH, ranging between 1 and 33%, stimulates activities of alpha-amylase and alpha-glucosidase in the hepatopancreas. High levels of glucose in hemolymph and of glycogen in the hepatopancreas were reached at the highest level of dietary CBH; however, the kinetics of accumulation is different. Shrimps fed with low level of CBH needed 3 h to reached glucose peak, whereas only 1 h is necessary for high CBH levels. A saturation curve was observed in glycogen level and alpha-amylase activity with maximum values in shrimp-fed diets containing 21% CBH. This level could be used to be included as a maximum shrimp dietary CBH level. Pre-prandial glycogen levels were observed in shrimp fed a diet containing 1% CBH, indicating an important gluconeogenesis, which affected the protein metabolism. The present results show that a diet containing 10% CBH may not be enough to cover the CBH requirement, which could be satisfied by dietary protein content. The low osmotic capacity observed in shrimp fed on a diet containing 10% CBH coincided with a relatively low post-prandial nitrogen excretion which reflects a low concentration of amino acids circulating in hemolymph, which affected the osmotic pressure and the osmotic capacity. These results reflect the high plasticity of shrimp species to use protein to obtain metabolic energy from food and its limited capacity for processing dietary CBH.