© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Direct measurement of the swimming speed, tailbeat, and body angle of Japanese flounder (Paralichthys olivaceus)
a Graduate School of Fisheries Sciences, Hokkaido University Minato 3-1-1, Hakodate 041-8611, Japan
b National Institute of Polar Research Kaga 1-9-10, Itabashi, Tokyo 173-8515, Japan
c Field Science Center for the Northern Biosphere, Hokkaido University Minato 3-1-1, Hakodate 041-8611, Japan
*Correspondence to R. Kawabe: tel: +81 95 819 2803; fax: +81 95 819 2799. e-mail: kawabe{at}net.nagasaki-u.ac.jp.
It is well known that flatfish species such as plaice can utilize the selective tidal stream to conduct vertical movements. However, detailed description of actual swimming behaviour is lacking, principally as a result of the difficulties encountered in monitoring the behaviour of flatfish in the open sea. The present study describes the use of a newly developed data-logger in obtaining simultaneous recordings of the swimming speed, depth, tailbeat, and body angle of free-ranging Japanese flounder (Paralichthys olivaceus) in the open sea. Our data indicate that Japanese flounders adopt a tailbeat-and-glide behaviour. They are found to glide downward without tailbeats for propulsion, and only during the ascent phase are tailbeats conducted. Flounders move horizontally at speeds of 0.59–1.23 km d–1 and at a maximum speed of 0.70–0.82 km h–1 in the open sea. Modal flounder swimming speeds are 30–40 cm s–1 (0.57–0.76 and 0.58–0.77 BL s–1), i.e. sometimes lower than the threshold of the speed sensor. In most cases, however, tailbeat oscillations occur at frequencies of 1.2–1.4 Hz. Moreover, flounders travel at a significantly steeper angle during the ascent phase than during the descent phase. In both cases it is believed that flounder optimize the energetic costs of migration, as has been shown for tuna, sharks, and seals.
Keywords: acceleration, beat-and-glide behaviour, body angle, Japanese flounder, swimming speed, tailbeat frequency, vertical movement
Received 16 March 2003; accepted 26 May 2004.
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  K. Sato, Y. Watanuki, A. Takahashi, P. J.O Miller, H. Tanaka, R. Kawabe, P. J Ponganis, Y. Handrich, T. Akamatsu, Y. Watanabe, et al. Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans Proc R Soc B, February 22, 2007; 274(1609): 471 - 477. [Abstract] [Full Text] [PDF]
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