IDEAL PROTEIN CONCEPT AND ITS APPLICATION IN PRACTICAL DIETS FOR NILE TILAPIA Oreochromis niloticus

Lay Nguyen, D. Allen Davis, Guillaume P. Salze, Shimaa M. R. Salem
School of Fisheries, Aquaculture and Aquatic Sciences
Auburn University, Auburn, AL 36849
davisda@auburn.edu
 

Nutritional methodologies applied to formulating cost effective feeds is often geared towards using low protein diets or inexpensive protein sources. However, this can result in an imbalance of amino acid profiles of feed, causing impaired growth, and reduced feed efficiency. Therefore, it is necessary to optimize amino acid balance in diets for fish. Like other fish species, researches on the balance of indispensable amino acid (IAA) and dispensable amino acid (DAA) for promoting maximum growth and protein deposition on Nile tilapia have been limited and inconsistent. Considering the importance of meeting amino acid requirements, this research sought to further optimize amino acid balance of the diets offered to Nile tilapia Oreochromis niloticus by applying and validating the use of the ideal protein concept. The efficacy of reduced protein diets and the effects of IAA supplements was evaluated in the first study. The results of this study indicate that the utilization of balanced IAA profiles of feed (under the application of the ideal protein concept) can help the fish to attain better growth performance and feed utilization efficiency. With the use of balanced IAA diets, the percentage of intact protein inclusion of feed can be reduced from 32% to 27.2% without causing impaired growth performance and feed utilization efficiency of fish. Further reduction of intact protein levels to 24.7% and 22.2% of diet, however, induced growth depression which could result from the deficiency of nonspecific nitrogen as a source of energy or limitation of daily IAA intake. In our ingredient matrix, in addition to lysine, methionine and threonine, it was hypothesized that tryptophan, isoleucine, arginine, histidine and valine could also be limiting. Hence, the following study was conducted to confirm a potential deficiency of these IAAs in our matrix of ingredients. These IAAs were individually deleted from the IAA profile of the diet with enhanced IAA (the IAA profile of diet which supported the highest growth of fish in the first study) and DAA supplements. The results illustrated that with the exception of valine, the deletion of the other crystalline IAA supplements (tryptophan, arginine, threonine and isoleucine) did not cause any deleterious effects on growth performance and protein utilization efficiency of fish. Therefore, in addition to lysine, methionine and threonine, valine is limiting in our ingredient matrix and the supplementation of this IAA is necessary to meet the requirement of fish. While tryptophan, histidine, arginine and isoleucine are likely adequate for growth of fish. The supplementation of DAA to spare the use of relatively expensive IAA was also taken into consideration by revising the ideal protein concept. Based on the growth data obtained from this study, it can be concluded that DAA plays an important role in meeting the nonspecific nitrogen requirement of fish. In a low protein diet (22.2%), enhancing IAAs above the requirement (120% NRC or to the IAA profile of the reference diet which supported highest performance of fish) did not help the fish to reach comparable weight gain to fish fed the diet with DAA supplements (4%). The results of this study also indicated the inferior growth of fish fed diet with IAA supplements at 100% NRC requirement and 4% DAA supplements which might result from limitation of daily IAA intake.