Histological studies on post-embryonic development of digestive system of seahorse Hippocampus kuda

The post-embryonic development of the digestive system of seahorse Hippocampus kuda,an ovoviviparous teleostean,was examined histologically from one day post-hatch to three months post-hatch.The result showed that the oesophagus,intestine,rectum,liver and cholecyst had already come into being in the digestive system after hatching from brood pouch of the male parent seahorse,however, the larvae still gained essential nutrition from yolk and tiny animal baits until five days post-hatch,when the larvae depended on feed from the environment completely.There was a critical period of high mortality for the seahorse during the development,it was at the ninth day after hatching;and the histological character began to be more complex just at this stage.In contrast with the larval stage,one-month old seahorse had a more perfect digestive system.The forepart of the intestine showed a Z configuration,and the intestinal wall was thick,especially its muscle layer.The liver was dramatically big so as to fill up the half part of the coelom;in contrast,the pancreas was dispersed among the liver and developed into a separate organ.Generally,the digestive system of seahorse has already matured after hatching for 3 months,which guaranteed that seahorse could digest and assimilate large animal feed,such as Acetes spp.and Mysis spp.Seahorse was also found to be a non-stomach teleostean.The study demonstrated again that the morphological and histological digestive features of seahorse always benefit its feeding activity.