Abstract
Two subspecies of ayu, Plecoglossus altivelis altivelis (nominotypical subspecies) and P. a. ryukyuensis (Ryukyu-ayu), differ morphologically, behaviorally, and genetically. Specimens from nine populations comprising both subspecies were investigated to examine whether their meristic characteristics follow a widely observed geographical tendency known as Jordan’s rule. Seven out of the eleven characteristics increased in frequency with latitude, following Jordan’s rule. Contrarily to the expectation from Jordan’s rule, however, Ryukyu-ayu had more anal fin rays than nominotypical subspecies in the temperate zone, suggesting genetic divergence underlying this characteristic between these two subspecies. The two subtropical populations showed a reversal of the geographic cline in the number of scales and dorsal fin rays, indicating these do not share a gene pool. The present study, without using genetic indicator, remains disputable to consider genetic status within Ryukyu-ayu further.
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Acknowledgments
We would like to express our gratitude to the personnel from Churaumi Aquarium, who allowed us to use specimens of extinct ayu from Okinawa-jima Island. We pledge that the use of the fish specimens in the present study was performed in compliance with the current laws of Japan and the Guidelines for the use of fishes in research.
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Ha, L.M., Iguchi, K. Geographical continuity and discontinuity in the meristic characteristics of ayus of the southern subspecies Plecoglossus altivelis ryukyuensis. Ichthyol Res 68, 177–181 (2021). https://doi.org/10.1007/s10228-020-00766-2
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DOI: https://doi.org/10.1007/s10228-020-00766-2