ontogeny of gut function in
marine fish larvae
I. Rřnnestad
Abstract:
Our current research focuses on ontogeny of digestive
function in marine fish larvae. Particularly, the intestinal digestion and
assimilation processes of dietary amino acids, and the hormonal control of
intestinal function. Our current experimental system provides a unique
opportunity for such studies. The set-up consists of controlled micro-tube
feeding of the larvae in combination with metabolic tracer studies enabling
us to quantify the intestinal proteolytic capacity, transfer kinetics of
nutrients from gut to body and the metabolic fate of essential and
non-essential amino acids. Data show that dietary free amino acids (FAA) are
absorbed faster (about 3.5 times in Senegal sole and 10 times in Atlantic
halibut) from the gut into the larval body tissues compared with the
protein. The FAA was also assimilated with higher efficiency than the
protein (>80% vs >60%). Our recent data indicate that a key intestinal
regulatory peptide (cholecystokinin, CCK) is not present until two weeks
after first feeding in Atlantic halibut. This raises the question of how
digestion is regulated during this vital developmental window. In larval
herring we have found a correlation between CCK and trypsin activity in
larvae upon tube feeding dietary protein. The response was much lower in
larvae fed FAA. We have recently demonstrated a marked, relatively rapid
retrograde peristaltic activity in the pyloric region of larval Atlantic
halibut, Hippoglossus hippoglossus L. in vitro and in vivo.
This could provide a mechanism by which the fish can fill the pyloric caeca
and seems also to be involved in mixing the chyme with digestive secretions
in the region of the pyloric caeca. These findings will be discussed in
relation to formulation of starter diets for marine fish.
(Department of Zoology, University of Bergen, Allégt
41, N5007 Bergen, Norway)