Determination of the freshwater mark in otoliths of Japanese eel elvers using microstructure and Sr/Ca ratios

Yutaka Kawakami, Noritaka Mochioka, Koichiro Morishita, Hidctoshi Toh, Akinobu Nakazono

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Abstract

The microstructure, in particular checks within the otolith edge, of Anguilla japonica glass-eels and elvers and changes in otolith Sr/Ca ratios were examined to ascertain the environmental history of the eels, especially with regard to the time when glass-eels entered the river, and as a benchmark for count daily increments. The percentage of glass eels and elvers with checks and the mean number of checks within the otoliths of glass-eels caught at four localities, Tosa Bay off Tosa City, the mouth of the Gokase River, the mouth of the Saigo River and the dam of the Tsuri River were 0% (0), 15.0% (0.2), 51.6% (1.0) and 100.0% (4.2), respectively. The Sr/Ca ratios and Sr content peaked in the region where checks were formed and the values decreased rapidly towards the edge of the checks; on the other hand, these decreased gradually in the otolith when checks were not formed. These checks were estimated to be formed by stress when the glass-eels were affected by ambient fresh water within the river. The innermost check was called the 'freshwater mark' in the present study and this mark may be useful as a benchmark in studying the growth history of the eel before and after entering freshwater.

Original languageEnglish
Pages (from-to)421-427
Number of pages7
JournalEnvironmental Biology of Fishes
Volume53
Issue number4
DOIs
Publication statusPublished - Jan 1 1998

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All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science

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