Seasonal appearance and size of newly-hatched larvae of Ryukyu-ayu Plecoglossus altivelis ryukyuensis in the Yakugachi and Kawauchi Rivers, Amami-oshima Island, southern Japan
2004
Kishino, T. (Kagoshima Univ. (Japan). Faculty of Fisheries) | Shinomiya, A.
To clarify the hatching season and size of the Ryukyu-ayu, Plecoglossus altivelis ryukyuensis, newly-hatched larvae were collected in the Yakugachi and Kawuchi Rivers, Amami-oshima Island, between November-March in 1995, 2001 and 2002. Hatching began from mid-November when the water temperature had decreased to about 18 deg C. This was compared with hatching onset dates recorded for Ayu P.a. altivelis at various locations around Japan, a significant negative correlation between latitude and onset of hatching being found. This was believed due to the lowering of water temperatures being delayed in the more southern latitudes, hatching starting when water temperature had decreased to around 20 deg C. The notochord length of newly-hatched Ryukyu-ayu larvae increased and water temperature decreased with each month. Larger larval size provide greater resistance to low water temperatures.
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