Ecological aspects of the Japanese eel, Anguilla japonica, collected from coastal areas of Japan.

The ecological characteristics of 597 yellow and silver-stage Japanese eels, Anguilla japonica, were examined and compared among collection sites located at three different latitudes of Japan (Amakusa Islands, Mikawa Bay, and Sanriku Coast) to provide basic data on this unusual catadromous fish species. Eels were sexed and their total length, body weight, age, and growth rate based on otolith analysis was compared among sexes, stages, and collection sites. The overall sex ratio favored females (94%), but the sex ratio differed among the three locations. The frequency of females was highest in the coastal waters at Sanriku in the north (100%), next highest at Mikawa Bay in central Japan (95%), and lowest in the Amakusa Islands in the south (70%). Silver eel males ranged from 41.2-66.3 cm in length and 4-10 years in age, and silver eel females from 44.3-97.2 cm in length and 5-17 years in age. Female eels generally grew faster (8.7+/-2.2 cm/year) than males (6.4+/-2.6 cm/year), and the growth rate slowed in the older eels. The growth rate of A. japonica at all three sites was much faster than that of other temperate anguillid species (< 4 cm/year), and their age at maturation was younger than that of other temperate species (approximately 7 to > 50 years), suggesting this species has important ecological differences from other similar species.