| Summary: | Considerable effort has been invested into the development and validation of alternative feed formulations forshrimp. Based on the PI’s experience with the transfer of this technology to feed manufactures, the primaryconstraint is a poor understanding or a lack of defined studies that pinpoint the methionine or total sulfur amino acid(methionine + cysteine) requirement of shrimp. Many feed manufactures have the methionine requirement setrelatively high which favors the inclusion of expensive fishmeal vs that of non-marine protein sources. Givencurrent economic and social concerns, this is not a sustainable approach. There are several publications evaluatingmethionine supplements to Pacific white shrimp feeds. Yet these papers do not provide a clear definition of therequirement, which is a major constraint to feed manufactures acceptance of low fishmeal feed formulations. Onetheory often presented, is that crystalline amino acids are absorbed and circulate in an asynchronous patter to thosefrom intact proteins. Based on current research we have demonstrated that the uptake of amino acids in shrimpcorresponds to the digestive physiology of the animal. In that, shrimp are semi-continuous feeders that process anddigest foodstuffs very quickly. From the initiation of feeding, an upswing in amino acids in the hemolymph wasapparent within 10 minutes confirming very quick processing and digestion of nutrients. The clearance of aminoacids was also relatively fast with amino acid levels returning to overnight fasting levels within 60 minutes offasting. This cycle of nutrient cycling corresponds to the semi-continuous feeding habits of shrimp. Based on bothabsorption and clearance patterns of the amino acids, there was no indication of a synchronous absorption ofsupplemented amino acids; hence, crystalline amino acids should be available for metabolism. Hence, if we canproduce a deficient diet, we should be able to induce a classic dose response. Across numerous growth trials,published and unpublished, the response of juvenile shrimp to a range of methionine sources have been evaluatedsuch sources include Dl-methionine, Micro-encapsulated methionine, coated methionine, synthetic peptides andvarious chelated forms. Yet, within the published literature there is little consistency of responses or any definitivestudies. Many of these studies present contradictory or inconsistent data and hence do not provide strong evidencefor a definitive requirement. Within our laboratory, across numerous independent growth trials, increasing the levelof methionine as a supplement or using corn protein concentrate as an intact protein source, increasing methioninelevels of the diet produced very little evidence of growth enhancement or no consistency of the response. In thisauthors opinion, inconsistent responses are due to other factors and the methionine requirement for this species isDavis, A. and M. Duan. 2017. Fact or Fiction: Methionine Requirement for Pacific White Shrimp Litopenaeus vannamei. En: Cruz-Suárez, L.E., Ricque-Marie, D., Tapia-Salazar, M., Nieto-López, M.G., Villarreal-Cavazos, D. A., Gamboa-Delgado, J., López Acuña, L.M. y Galaviz-Espinoza, M. . (Eds), Investigación y Desarrollo en Nutrición Acuícola Universidad Autónoma deNuevo León, San Nicolás de los Garza, Nuevo León, México, pp. 32-54.quite low and may not be a limiting amino acid in many commercial feed formulations. The alternative hypothesis,is that many of our purified forms are not available to shrimp or that test diets and systems are not appropriate.Clearly, there is a need to better understand amino acid metabolism in shrimp and define limiting amino acids aswell as techniques to consistently define amino acid requirements.
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