To determine the effect of environmental factors on otolith increment deposition in Japanese eel, Anguillu juponicu T. & S., a total of 337 elvers with a tetracycline time mark in the otolith were reared for 50 days under various experimental temperatures (12, 19 and 25" C), feeding rations (fed and unfed)and salinities (one-third sea water of I 2 k a n d freshwater). Fish were sequentially sampled after 5. 15,30 and 50 days and their sagittal otolith increments were observed. Under fed conditions at 19 and 25" C, daily increment deposition was observed throughout the 50-day period. In unfed groups and/or at 12" C, the rates of increment deposition were reduced sharply after the fifth day and no clear increments were added. No difference was obtained in increment deposition rates between one-third sea water and fresh water groups. Increment deposition rate was independent of otolith and body size.

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Results of age determination of Anguilla japonica leptocephali collected in the Western North Pacific, 16•‹29'N, 139•‹21'E in July 1990 are presented. The mean age of 18 leptocephali of 19.5-25.4mm TL was estimated to be 35.2 d. Backcalculated birth dates ranged from 26 May to 12 June 1990, with a mean birth date of 2 June 1990. This value was about one month earlier than

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