Expression and activities of
pancreatic enzymes in developing sea bass larvae (Dicentrarchus labrax)
in relation to intact and hydrolyzed dietary protein; involvement of
cholecystokinin
C. Cahu, I. Rønnestad, V. Grangier, J.L. Zambonino
Infante-2004
Aquaculture, 238: 295-308
Abstract:
In order to assess the influence of dietary protein
on digestive enzyme expression and cholecystokinin (CCK) content in sea bass
larvae, four groups of larvae were fed experimental diets from mouth opening
until day 42: three isonitrogenous diets with increasing protein hydrolysate
levels (0%, 14% and 46% of crude matter) and one diet incorporating starch.
The groups fed high starch or high protein hydrolysate level exhibited the
lowest growth. The final weight in these groups was 9.5 and 5.6 mg,
respectively, whereas it reached approximately 20.0 mg in the groups fed 0%
or 14% protein hydrolysate level. The highest levels of trypsin secretion
were observed in larvae fed the lowest protein hydrolysate level.
Paradoxically, the groups fed diet containing starch also exhibited a high
trypsin secretion level. There was a clear allometric relationship between
larval CCK content and body mass, but there were also differences between
dietary groups. On day 42, the CCK level in the group fed diet incorporating
starch (40 fmol/mg dry weight of larvae) was more than twice as high as that
found in the other groups. The lowest CCK level (13 fmol/mg) was found in
the group fed the highest protein hydrolysate level. Our data suggested that
dietary protein level and chain length combined with protein intraluminal
proteolytic activity regulate the CCK level in fish larvae as in other
vertebrates. The CCK concentration assayed in larvae fed diets with a low
protein content or different protein hydrolysate levels is compatible with
the existence of an indirect mechanism controlling CCK release and mediating
pancreatic enzyme secretion.