Development of digestive organs and feeding ability in larvae of Japanese eel (Anguilla japonica)

As part of a study on the early life of Japanese eel, the development of the digestive organs was observed during the 13 d after hatching. The digestive tract was formed only at the pharynx at hatching; the posterior part of the duct differentiated during 1 d posthatch (DPH). Pancreas and liver started to develop at 3 DPH. Immunohistochemistry using an antibody to eel trypsinogen showed weak signals first appearing in the pancreas at 6 DPH, suggesting that the eel pancreas starts to synthesize digestive enzymes at 6 DPH. The immunohistochemical signals became strong at 7 DPH, at which time the mouth opening orientation moved from ventral to anterior, the intestine differentiated into small intestine and rectum and the yolk was absorbed. Rotifers were first observed in the digestive tract of 13-d-old larvae. We inferred from the developmental process of the digestive organs that the larvae can start feeding at 7 DPH, which is earlier than observations of first feeding.