Development of endocrine system regulating exocrine pancreas and estimation of feeding and digestive ability in Japanese eel larvae

To investigate the feeding and digestive physiology of early eel larvae, the development of cholecystokinin (CCK) and peptide YY (PYY) in the larval intestine, the feeding speed and pancreatic trypsin secretion in response to feeding were observed. CCK and PYY mRNA started to be expressed in the larval intestine at 8 days post-hatching (dph). This indicates that the pancreatic enzyme secretion is probably controlled by the CCK and PYY endocrine systems from the first feeding. Using fluorescein isothyiocyanate isomer (FITC)-labeled freeze-dried shark egg powder (Aquaran) as a diet, 10-dph eel larvae were estimated to feed at a rate of 0.04 μg Aquaran/min. The tryptic activity in the intestines of 11-dph larvae increased approximately 4.2-fold at 1 h of feeding, whereas that in the pancreas remained constant. These results indicate that the digestive tract of these larvae recognized Aquaran as a nutrient, and that the exocrine pancreas secreted digestive enzymes into the intestine and began to synthesize digestive enzymes in response to feeding.