Back-calculated annual growth of 156 yellow-phase female Japanese eels Anguilla japonica sampled from freshwater sites in the Tsuchikawa River, Kagoshima, Japan, were compared among eels from the upper reaches (“upstream emigrants”), large eels (≥240 mm) from the lower reaches (“downstream residents”), and small eels (<240 mm) from the lower reaches (“undetermined”, including future emigrants and residents) to elucidate the possible relationships between growth conditions and habitat selection by Japanese eels. The youngest eels caught in the lower reaches were 1 year of age, whereas eels in the upper reaches were >3 years of age. Back-calculated annual growth of large eels captured in the lower reaches was significantly greater than that of eels in the upper reaches for the first 3 years after recruitment (age 0–2 years), and small eels in the lower reaches had intermediate growth. These results suggest that female eels in this river decide whether to emigrate or reside in the lower reaches approximately 3 years after recruitment, and that slower-growing eels emigrate upstream, whereas faster-growing eels reside downstream.
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