Page 13 - PII: S0044-8486(99)00371-3

)
D. Lemos et al.rAquaculture 186 (2000 89–105 101

Fig. 7. Relationship between APD and DH of some meal samples ŽTable 2 in juveniles L. Õannamei
.
ŽEzquerra et al., 1998 . DH measured by the pH-stat method at 258C. APD was determined by the chromic
.
oxide method ŽCho and Slinger, 1979; Tacon and Rodrigues, 1984 . Significant correlation at P-0.05.
.
protein in crustacean seafood occurs rapidly after harvest and has been attributed to
digestive proteases ŽSalem et al., 1970 . As observed in other cultured animals, the
.
activity of shrimp digestive proteinases seems to be stimulated by low quality feeds ŽLee
´
and Lawrence, 1986; Rodrıguez et al., 1994; Le Moullac et al., 1996; Lemos and
´
Rodrıguez, 1998 .. Thus, the supply of a low nutritional quality feed may reduce the
shelf life of shrimp ŽNip et al., 1985 , decreasing its trade value. Both trypsin and
.
chymotrypsin of L. Õannamei had higher activities when fed with a low quality protein
meal Žmenhaden B when compared to other feeds Table 2 . The low nutritional value
.
.
Ž
of feeds containing menhaden B meal may be due to the heat-treatment during drying
which decreased the amount of some essential amino acids available in the feed
ŽEzquerra et al., 1997b . In shrimp farming, the use of low quality feeds may result in
.
lower growth rates but also in the reduction of the product storage life.
Penaeid nutritional background is scarce and few research projects are devoted to
understanding the biochemical capabilities of shrimp during digestion. So far, most of
the proteinases in the shrimp digestive system have been described and some have been
characterized ŽMaugle et al., 1982; Van Wormhoudt et al., 1992; Hernandez-Cortes et
´
´
al., 1997 .. There is evidence that some of these proteinases are translated as zymogens
ŽSellos and Van Wormhoudt, 1992 . However, the zymogen has never been isolated.
.
Recently, an inhibitor for trypsin was found in L. Õannamei digestive gland ŽGarcia-
Carreno et al., 1999 .. There is a lack of information about the transcription and
˜
translation processes as well as the mechanisms of regulation of both processes. It is
unclear if the enzymes are constitutive or inducible, how many mRNAs are coded and
their half-life, and how many proteins are translated by any mRNA. Also, posttrans-