Ultrastructure of Hepatocyte and Liver Ontogeny of the Indo-Pacific Seahorse Hippocampus barbouri Jordan & Richardson 1908

Abstract

The Indo-Pacific seahorse, Hippocampus barbouri, is one of the most important marine fish and a potential target of aquaculture, but basic biological information on this fish is largely missing. In this study, we described the hepatocyte ultrastructure and the ontogeny of the liver in H. barbouri during the 1^st and the 35^th day after birth (DAB). The histological observation of the liver structure identified that hepatocytes have a centrally placed oblong to round nucleus surrounded by the basophilic cytoplasm. Extensive accumulation of lipid droplets and glycogen was observed in the cytoplasm of the hepatocytes. Transmission electron microscope observation confirmed that the hepatocytes contained cisternae of granular endoplasmic reticulum associated with mitochondria of various shapes. Secretory granules of uniform density were scatted in hepatocytes, which were considered as the glycogen storage granules. According to the liver ontogeny analysis, the basic liver structure such as a network of the hepatocyte and sinusoid capillary was present at the 1^st DAB and a large amount of collagen accumulation was observed by the 14^th DAB. These results increase the knowledge about the initial development of H. barbouri, which will be useful to assess nutritional status of this species during aquaculture development.