Efficacy of Purified Amino Acids in Practical Diets for Pacific White Shrimp Litopenaeus vannamei
Type of DegreeMaster's Thesis
Fisheries and Allied Aquacultures
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Shrimp growth and nitrogen loading is influenced by the quantity and quality of protein supplied to the diet. Protein is also the main cost component of the diet, and, therefore, feed formulations need to be cost effective. Feed formulations are moving towards using less fishmeal in diets and more plant-based protein sources, which are cheaper and more widely available. However, plant protein sources have some disadvantages and one of the major problems are unbalanced amino acid profile. To meet an amino acid requirement, a combination of different ingredients may be used, or the diet may be supplemented with crystalline amino acids (CAA). Formulations now are “nutrient-based” as shrimp have a requirement for amino acids rather than for protein which makes the determination of essential amino acid requirements important. Studies determining amino acid requirements have been variable and opinions differ on whether CAA are utilizable by shrimp due to their slow feeding habits. Other possible causes of this variation are unclear but there could be some environmental factors or differences in experimental design limitations. Lysine and methionine are often the most limiting amino acids in plant-based diets. Methionine is an amino acid that is often supplemented in shrimp diets when soybean meal is the main protein source which is known to be deficient in sulphur containing amino acids. Reported methionine requirement is quite high and studies are variable and often not repeatable. Before a methionine requirement can be determined a suitable source that produces a response needs to be identified. Consequently, the objective of the first study was to determine the efficacy of CAA in diets of Pacific White Shrimp. For this experiment, a basal diet was designed to have 30% crude protein (CP) and 6% lipid. The CP was then decreased gradually to reach 28, 26, 24 and 22% CP in the first series. In the second series of diets, CAA was supplemented back to each of the lower CP diets to reach 30% CP of the basal diet. Limited statistical differences were found but, as the CP content of the diet decreases the percentage weight gain (PWG) and mean final weight (MFW) was significantly affected. None of the diets supplemented with CAA seemed to produce the same performance as that of the 30% CP diet. A second study was then formulated to determine the effect of protein level on CAA supplementation. A fishmeal-based reference diet was formulated, as in theory, fishmeal should be replete in essential amino acids required by this species. Two soybean meal-based diets were then formulated to reach 30 and 35% CP and each supplemented with essential amino acids in one set and methionine in another to reach the same level as a percent protein as that of the fishmeal reference diet. In terms of PWG, no significant differences existed among the diets, but in terms of protein retention efficiency (PRE), the fishmeal diets produced significantly higher performance compared to most other treatments. The last study looked at the efficacy of different methionine sources when supplemented to a soybean meal basal diet. Methionine (Met) was supplemented to reach 0.60% (by using DL-Met, coated Met, peptide Met and intact protein Met) of the diet from a basal diet containing 0.45%. However, none of the supplemented sources significantly improved performance of the shrimp leading to the conclusion that methionine may actually not be deficient in a soybean diet for Pacific White Shrimp. There is a clear need to find suitable sources that can be used for determining essential amino acid requirements, which may then also be used for diet supplementation in the industry. As per overall observation during the present study, it was not clear whether purified amino acids are effective in the diets of Pacific White shrimp or if a practical diet designed to be low in methionine is actually deficient.It may be necessary to complete further research to determine what the cause may be for the poor utilization of CAA. Poor utilization is likely due to leaching but other factors such as pH of the diet, absorption from the gut and palatability may also be considered.