Synchronous changes of morphology and gonadal development of silvering Japanese eel Anguilla japonica

The gonadal development of Japanese eel Anguilla japonica during silvering was examined via gonadal histology and morphometric characteristics. Specimens were collected from the Kaoping River of Taiwan between November 1998 and November 2001. Female eels predominated, constituting 87.6% of the sex-determined eels. The degree of gonadal development was assessed by skin coloration, with female eels divided into yellow, pre-silver, and silver phases. Males were divided into yellow and silver phases because of small sample size. Silver phase eels predominated in the winter. Mean (±S.E.) total length of silver-phase eels was significantly larger in females (642.2±10.4) than males (564.8±14.6) ( p