|Fish meal is preferred among other protein sources because it is an excellent source of essential nutrients such as protein and indispensable amino acids, essential fatty acids, cholesterol, vitamins, minerals attractants and unidentified growth factors. The cost of fish meal has increased over time because of increased demand, limitations of availability, and growing social and environmental concerns regarding wild fish extraction practices. To develop sustainable and environmentally friendly aquaculture, various plant-based ingredients that contain high protein content are potential alternative sources for fish meal. Among plant protein sources, soybean meal is the most utilized and has received considerable attention as a replacement for fish meal in aquatic animal feeds because of its availability, low price, reasonably balanced amino acid profile and consistent composition. However, the presence of anti-nutritional factors such as phytate and non-starch polysaccharides (NSPs) limited the supplementation level of soybean meal in some aquaculture feeds. In order to deal with the negative effects caused by phytate and NSPs, exogenous phytase and carbohydrase are utilized as feed additives in soybean meal based diet. The second chapter in this research was to evaluate the growth response and apparent digestibility coefficients to practical diets containing grade level of phytase. Results of this study revealed that 2000 IU/kg feed phytase was the recommended addition level in terms of improving phosphorus (P) and protein availability. Growth performance was not affected by phytase supplementation, which indicated that the possibly improved P and protein availability did not pose a significant effect on growth response. Copper content in the whole shrimp body was significantly increased in the treatment supplemented with 1000 IU/kg feed phytase, which indicates that the addition of phytase to a soybean meal based diet might increase bioavailability of copper, thereby increasing whole body copper deposition. The third chapter of this study investigated the growth performance and apparent digestibility coefficients of Pacific white shrimp responded to carbohydrase incorporation in the soybean meal based diets. Results showed that 0.02% carbohydrase inclusion significantly improved protein digestibility and numerically (P-value=0.0863) increased energy digestibility for more than 3%. However, growth performance was not affected by carbohydrase supplementation, which indicated growth performance responded to the possibly enhanced protein availability was not significant.
Overall, results from these studies reveal that the use of feed additives phytase and carbohydrase should be encouraged in shrimp feed formulation. However, more studies will be needed to further determine the best inclusion level of carbohydrase in terms of protein and energy digestibility and investigate the combined effects of organic acids (as acidifier) and phytase or carbohydrase on the performance of Pacific white shrimp.