On the Juvenile of Anguilla marmorata QUOY et GAIMARD in Yakushima (Yaku Island) : Its Ecology and Morphorogy

The authors had investigated the ecology and morphorogy of the juvenile stage of a tropical eel, Anguilla marmorata QUOY et GAIMARD, through 1966-67 at the Isso River in Yakushima (Yaku Island, 30°26'N 130°30'E), Kagoshima Prefecture. The elvers and youngs up to 300 mm in length live under the small rocks and boulders rolling on the sandy bottom in the middle or lower reaches of the river (for examples, at the section b indivision A and the section e in division B in Figs. 2 and 3). The larger eels are fond of the crevices of the large rocks. The vertebral number of the collected specimens are shown in Fig. 5. Their range distributes from 101 to 107, and the average is 104.63. The smallest specimen collected during this investigation is 48.0 mm in length. In the specimens about such a size, the morphorogical characters and the pigmentation indicate the V-VI stages-elver by BERTIN (1956). The anadromy of the elvers seems to begin in October, ascend abundantly in November to January, and last to May or June. Differing from temperate eels, such as A. japonica, the tempreture of sea water in the coastal region is much higher than the river through the anadromous season