Effect of dietary cornstarch levels on growth performance, digestibility and microscopic structure in the white shrimp, Litopenaeus vannamei reared in brackish water

The ability of Litopenaeus vannamei (initial mean weight: 0.96 +/- 0.02 g) to utilize different levels of cornstarch was examined in terms of growth indices, body composition, digestibility and microscopic structure of the hepatopancreas. Six isonitrogenous semipurified diets were fed to satiation to shrimp for 8 weeks in triplicate tanks (30 shrimps per tank) connected to a natural brackish water (6-8 g L-1) recirculating system. Diets contained different levels of cornstarch (100, 150, 200, 250, 300 and 350 g kg(-1)) as the source of carbohydrate and were balanced using cellulose. Weight gain (WG), survival rate and feed conversion rate (FCR) were considerably affected by cornstarch levels of diets. The highest WG (453.6 g kg(-1)) and best FCR was observed in shrimp fed the 150 g kg(-1) (cornstarch level) diet and was significantly (P < 0.05) higher than those fed diets containing 250-350 g kg(-1) cornstarch. However, the survival rate reached maximum in shrimp fed the 100 g kg(-1) diet (96.7), some 30% higher than the lowest rate, which was found in shrimp fed the 250 g kg(-1) diet. Body lipid tended to be higher in shrimp fed diets with higher cornstarch levels. The apparent digestibility of dry matter and crude fat increased with increasing levels of cornstarch and, hence, decreasing levels of cellulose. In addition, histological study on shrimp fed 10-350 g kg(-1) diets exhibited histological changes. The overall conclusion was that the optimum cornstarch level may be set at 100-200 g kg(-1) when the diets contain 380 g kg(-1) protein.