Protein digestion in penaeid shrimp: digestive proteinases, proteinase inhibitors and feed digestibility

Protein is the most abundant ingredient in both natural and prepared diets of penaeid shrimp. The assessment of protein digestion through the developm ental stages of penaeids may contribute to the development of more suitable feeding schedules for their cultivation. Among the techniques to study pro tein digestion, detection and characterization of digestive proteinase inhi bitors in proteinaceous feed ingredients can be achieved by substrate-[sodi um dodecyl sulphate polyacrylamide gel electrophoresis] (SDS-PAGE). In vitr o assays of protein digestibility are also useful tools when testing altern ative protein sources in the formulation of shrimp feeds. The present artic le reviews three methods that have been used to assess protein digestion: ( 1) detection and characterization of proteinase activity and proteinaceous proteinase inhibitors by substrate-SDS-PAGE, (2) quantification of proteina se activity, and (3) in vitro evaluation of digestibility of dietary protei n sources by shrimp proteinases. A compilation of previously reported and u npublished data on some aspects of penaeid protein digestion is presented. Trypsin activity of Litopenaeus schmitti varied considerably during larval and postlarval development, showing the highest value at protozoea III. The molecular weight of digestive proteinases from early stages of Farfantepen aeus paulensis also differed from the adult pattern, and some activity band s could be characterized as trypsin in adult F, paulensis. The digestive pr oteinase pattern of adult Farfantepenaeus californiensis, F. paulensis, L. schmitti and Litopenaeus vannamei in SDS-PAGE showed clear differences amon g these species, which may be evidence of a species-specific pattern of pro tein digestion. In vitro evaluation of digestibility of aquafeeds can be ac hieved by the pH-stat method, which can help in the choice for alternative protein sources. Moreover, the quality of postharvest shrimp may also be af fected by increased digestive proteinase activity that seems to be stimulat ed by low nutritional quality feeds. (C) 2000 Elsevier Science B.V. All rig hts reserved.