February 15-18, 2009 Washington State Convention Center Seattle ...

ONTOGENY AND CHARACTERIZATION OF SOME INTESTINAL ENZYMES IN COBIA
Rachycentron canadum LARVAE
Nguyen Quang Huy, Helge Reinertsen, Tran Mai Thien and Elin Kjørsvik
Norwegian University of Science and Technology
N7491 Trondheim , Norway
huy.nguyen@bio.ntnu.no
The ontogeny of some intestinal enzymes were investigated during the development of cobia (Rachycentron canadum) larvae
in order to determine the timing of intestinal maturation. The larvae in one treatment was fed live feed only (LF) and in another
treatment was co-fed with a microdiet (L-MD) from 17 to 27 days post hatching (dph), and then microdiet alone to the end of
the experiment at 33 dph. The larvae grew exponentially from initial standard length (SL) 3.1 ± 0.02 mm at hatch to a final SL
20.6 ± 0.6 mm in LF and 21.3 ± 0.6 mm in L-MD treatment, with no significant difference between the treatments (p> 0.05).
However, survival rate at 30 dph of larvae in L-MD treatment (9.6%) was about almost half of that in LF treatment (19.8%). In
addition to intestinal enzymes, the pancreatic enzyme trypsin was assayed. Individual activity of trypsin increased with larval
growth as expected in both treatments. The specific activity of brush border membrane (bbm) alkaline phosphatase (AP) was
abruptly elevated from 23 to 26 dph (twofold; p< 0.05) in LF treatment and from 26 to 30 dph (2.5-fold; p 0.05) and about threefold between 26-30 dph in L-MD treatment (p< 0.05). No significant increase
in specific activity of bbm leucine aminopeptidase (LAP) and ratio of bbm LAP/leu-ala during larval development in both
treatments suggesting that LAP was a less clear marker for intestinal maturation than AP in cobia. As the activity of bbm AP
has been well recognized as intestinal maturation marker, it can be assumed that intestine of cobia larvae attained maturational
stage when bbm AP activity reached its plateau at 26 dph (SL 17.0 mm; 699.3 degree days) in LF treatment and at 30 dph (SL
20.0mm; 814.0 degree days) in L-MD treatment. Weaning of cobia larvae as early as 17 dph thus delayed the intestinal maturation
process clearly and was associated with lower survival rate than that of LF treatment, although growth rate of the larvae
was not affected.
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