Histological ontogeny of the digestive system of marble goby (Oxyleotris marmoratus) larvae

The development of the digestive system in the larvae of marble goby Oxyeleotris marmoratus was examined histologically from the 2nd to the 35th day after hatching. The larvae absorbed their yolk sacs 4-5 days after hatching, however they commenced exogenous feeding 2 days after hatching. After the onset of exogenous feeding 5 regions could be easily distinguished in the gut: the buccal capvity, the oesophagus, a future stomach, the intestine and the rectum. At this time, the intestinal tract was functional however the stomach was not developed completely. The first signs of intestinal absorption appeared in day 3 after hatching and could be identified as lipid vacuoles in the rectum. The larvae started to absorb protein in day 5. The stomach formed from day 10 to 15 but only circular muscle layer was identified in the muscularis external. Liver and pancreas were formed and well-developed in the early larval period. After metamorphosis, the appearance of gastric glands in day 30 indicated that the development of digestive system was completed.