島根県の河川におけるミナミアカヒレタビラの生活史と季節移動

抄録

The life history and seasonal migration of the critically endangered freshwater fish Acheilognathus tabira jordani was studied in an undisclosed river in Shimane Prefecture, from April 2011 to November 2012. A total of 705 individuals were captured and marked by hypodermic injection of fluorescent elastomer tags, and released to clarify growth and migration of each individual. Based on ovulation and ovipositor length, breeding of A. tabira jordani occurred from ca. May 15 to July 20 in 2011, and ca. April 20 to July in 2012, peaking in May and June of both years. The 2011 spawning season started later, possibly due to lower water temperature in April, than in the following year. Oneyear-old fish formed two cohorts from April to June, possibly due to the differences in spawning time. The smaller cohort had a high growth rate from May to July, becoming integrated with the larger cohort in July 2012. This suggests that small cohort individuals invested their energy in growth without breeding. Mature female and male fish aggregated downstream, where mussels were abundant, during the main spawning season, but in upper streams waters in autumn and winter, where mussels were less abundant. The maximum distance migrated between the spawning and non-spawning seasons was estimated as ca. 5300 m.