IMMIGRATION PERIOD AND AGE OF ANGUILLA-JAPONICA GLASS-EELS ENTERING RIVERS IN NORTHERN KYUSHU, JAPAN DURING 1994

The immigration period, age at immigration, and hatching dates of 174 glass-eels Anguilla japonica caught in northern Kyushu during 1994 wer e examined, based upon continuous sampling and counting of the daily i ncrements of the sagittal otoliths. Immigration of glass-eels to north ern Kyushu occurred from February to July, four months later than on t he Pacific coast. Examination of otoliths showed that glass-eels had e ntered into freshwater at the mouth of rivers at the age of 169 +/- 15 days (mean +/- SD). Hatching dates extended from August 1993 to Janua ry 1994 and the mean ages of glass-eels of different hatch months were as follows: August-184, September-166, October-169 and November-168 d ays. The peak spawning month was September. Otolith microstructure sho wed three separable phases, i.e., leptocephalus stage, metamorphosing stage and glass-eel in sea water stage. Age at the freshwater mark and duration of the leptocephalus stage of August-hatched eels were signi ficantly older and longer, respectively, than those eels hatched in ot her months.