Morphological and histological changes in the swim bladder during maturation of the Japanese eel

Abstract

Silver eels Anguilla japonica ( I G 1·5–3·5) had more developed rete mirabile, gas gland and submucosa than yellow eels ( I G 0·4–1·5) and the development of swim bladder components increased with sexual maturity only in the early maturation process ( I G 3·5). These observations indicate that the Japanese eel develops its swim bladder in either the river or shallow sea water and leaves for the open sea after the swim bladder has become adapted to a deeper‐sea environment.