Ecomorphological dimorphism of juvenile <Emphasis Type="Italic">Trachurus japonicus</Emphasis> in Wakasa Bay,Japan |
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Authors: | Munenori Kishida Yu Kanaji Songguang Xie Yoshiro Watanabe Tomohiko Kawamura Reiji Masuda Yoh Yamashita |
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Institution: | (1) Biodiversity Policy Division, Nature Conservation Bureau, Ministry of the Environment, 1-2-2 Kasumigaseki, Chiyoda, Tokyo 100-8975, Japan;(2) National Research Institute of Far Seas Fisheries, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa, Yokohama Kanagawa, 236-8648, Japan;(3) Key Laboratory of Biodiversity and Conservation of Aquatic Organisms, Institute of Hydrobiology, Chinese Academy of Science, Wuhan, Hubei, 430072, China;(4) Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa Chiba, 277-8568, Japan;(5) Maizuru Fisheries Research Station, Field Science Education and Research Center, Kyoto University, Nagahama, Maizuru, Kyoto 625-0086, Japan |
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Abstract: | Morphometric analyses of marine pelagic fishes have generally been conducted for stock identification rather than for ecomorphological
understanding. Many papers on stock identification of Trachurus japonicus reported polymorphisms in the Japanese Islands waters. However, none of them has found polymorphism in fish less than 100 mm
standard length (SL), despite the environmental differences experienced by juvenile cohorts. The objective of this study was
to detect ecomorphological polymorphism of juvenile T. japonicus (<100 mm SL) in Wakasa Bay, Japan, where multiple juvenile cohorts appear. From analyses of size frequency distributions
and otolith microstructure, five cohorts were recognized in the bay from September 2003 to August 2004. We then compared 17
morphometric characters on body, fin, and otolith morphology, and found cohort-specific and roughly dimorphic pattern (a streamlined
morph and a compressed morph). The dimorphism was markedly observed in 50–70 mm SL, and was regarded as specific to the juvenile
stage by comparison with the senior dimorphisms (≥100 mm SL). Referring to the literatures on functional morphology, the streamlined
morph and the compressed morph were considered to be suitable to body and caudal fin (BCF) periodic propulsion and BCF transient
propulsion, respectively. The juvenile dimorphism was interpreted as adaptive in its developmental environments (i.e., ecomorphological
dimorphism) by relating the functional differences to the inferred ecological differences: the streamlined morph is adaptive
to feed on larval Engraulis japonicus in coastal waters, whereas the compressed morph is adaptive to associate with jellyfishes in offshore waters. |
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