Fact or Fiction: Methionine Requirement for Pacific White Shrimp

Resumen

Considerable effort has been invested into the development and validation of alternative feed formulations for
shrimp. Based on the PI’s experience with the transfer of this technology to feed manufactures, the primary
constraint 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 set
relatively high which favors the inclusion of expensive fishmeal vs that of non-marine protein sources. Given
current economic and social concerns, this is not a sustainable approach. There are several publications evaluating
methionine supplements to Pacific white shrimp feeds. Yet these papers do not provide a clear definition of the
requirement, which is a major constraint to feed manufactures acceptance of low fishmeal feed formulations. One
theory often presented, is that crystalline amino acids are absorbed and circulate in an asynchronous patter to those
from intact proteins. Based on current research we have demonstrated that the uptake of amino acids in shrimp
corresponds to the digestive physiology of the animal. In that, shrimp are semi-continuous feeders that process and
digest foodstuffs very quickly. From the initiation of feeding, an upswing in amino acids in the hemolymph was
apparent within 10 minutes confirming very quick processing and digestion of nutrients. The clearance of amino
acids was also relatively fast with amino acid levels returning to overnight fasting levels within 60 minutes of
fasting. This cycle of nutrient cycling corresponds to the semi-continuous feeding habits of shrimp. Based on both
absorption and clearance patterns of the amino acids, there was no indication of a synchronous absorption of
supplemented amino acids; hence, crystalline amino acids should be available for metabolism. Hence, if we can
produce 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published and unpublished, the response of juvenile shrimp to a range of methionine sources have been evaluated
such sources include Dl-methionine, Micro-encapsulated methionine, coated methionine, synthetic peptides and
various chelated forms. Yet, within the published literature there is little consistency of responses or any definitive
studies. Many of these studies present contradictory or inconsistent data and hence do not provide strong evidence
for a definitive requirement. Within our laboratory, across numerous independent growth trials, increasing the level
of methionine as a supplement or using corn protein concentrate as an intact protein source, increasing methionine
levels of the diet produced very little evidence of growth enhancement or no consistency of the response. In this
authors 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 de
Nuevo 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 as
well as techniques to consistently define amino acid requirements.