Age-dependent changes in the growth and reproductive patterns of the southern red tabira bitterling, Acheilognathus tabira jordani
Tamura, Moe | Ikeda, Saho | Nishio, Masaki | Kawakami, Ryosuke | Yamazaki, Yuji
The age structure, growth pattern, and reproductive traits of the southern red tabira bitterling, Acheilognathus tabira jordani, were investigated in a small pond in Toyama Prefecture, central Honshu, Japan. Analysis of 5,720 individuals over two years revealed the existence of three or four age groups in every month, and individuals born during the study years were observed after June. Individuals of two years of age and younger increased their body size in the spring and summer and maintained them in the winter, while individuals in the 3+ age cohort did not show noticeable increases in body size throughout the year. Based on the appearance of spawning-capable individuals, the oviposition period of the A. t. jordani population was estimated to range from late April to late August. Compared with the oviposition periods of populations in other regions, the period in the study area was delayed, probably as a result of lower water temperatures, especially in the summer. During the oviposition period, the proportion of spawning-capable individuals differed between age cohorts in both males and females; in younger individuals the proportion of ovipositors was higher in the early part of the oviposition period. Taking into consideration observed differences in growth and spawning patterns due to age, younger individuals appear to invest their acquired energy into their own growth, while older individuals invest it in spawning. The present study reveals that habitat conservation strategies for A. t. jordani should be determined for specific regions.
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