Distribution of ghrelin immunoreactivity in artificially reared Japanese eel, Anguilla japonica, leptocephalus and metamorphosed glass eel

Ghrelin plays a role in regulation of appetite and satiety, and the orexigenic effects of peripheral or central ghrelin administration in fish have been reported. Ghrelin distribution in artificially reared eel leptocephalus and metamorphosed glass eels were examined in the present study using immunohistochemical methods. Immunoreactivity was detected in spinal cord, mucinous pouch, vascular tubules, and skin of eel leptocephalus on various days-after-hatching. Moreover, predominant immunopositive reactions were detected in the vascular system, including heart, along with spinal cord, notochord, head kidney and skin of the metamorphosed glass eel. Ghrelin immunopositivity was elevated after development of hematopoietic and vascular systems of the metamorphosed eel. Ghrelin thus, has more marked effects on physiology after the metamorphosis stage in Japanese eel.