Immigration Patterns of Glass-Eels Anguilla Japonica Entering River in Northern Kyushu, Japan
Abstract:Immigration periods and growth histories of glass-eels, Anguilla japonica, caught in northern Kyushu during 1995 and 1996 were examined based upon continuous sampling and daily counts of sagittal otolith increments. Immigration periods of glass-eels in 1995 and 1996 occurred from January to June, 1 mo earlier than in 1994. Examination of otoliths showed that glass-eels had entered into fresh water at the mouth of the river at the mean age of 168 ± 20 and 172 ± 21 d (mean ± SD) in 1995 and 1996, respectively. Hatching dates spanned July to November 1994 and July to December 1995. Mean ages of glass-eels entering fresh water during 1995 and 1996 following different hatching months ranged from 164–174 d during the months of July–December. Back-calculation of the age from the catch date suggested that the peak of spawning season was in fall, that the peak metamorphosing season of leptocephalus was in winter, and that glass-eels immigrated into the rivers of northern Kyushu in December. The age at freshwater mark and durations of each stage, i.e., leptocephalus stage, metamorphosing stage, and glass-eel in the sea water stage, were not significantly different between hatching months. Conversely, comparing 1994 results and this study, the age at the freshwater mark and the duration of the leptocephalus stage of earlier hatched eels was significantly older and longer, respectively, than those eels hatched in other years. These results indicated that there were two different immigration patterns of glass-eels entering river of northern Kyushu during the three years, 1994, 1995, and 1996.
Document Type: Research Article
Publication date: 1999-03-01
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