Characterizing the escape response of juvenile summer flounder Paralichthys dentatus to diel-cycling hypoxia

Authors

  • D. C. Brady,

    Corresponding author
    1. University of Delaware, School of Marine Science and Policy, 700 Pilottown Rd, Lewes, DE 19958, U.S.A.
      Author to whom correspondence should be addressed at present address: University of Delaware, Department of Civil and Environmental Engineering, 301 DuPont Hall, Newark, DE 19716, U.S.A. Tel.: +1 207 312 8752; fax: +1 302 831 8402; email: damian@udel.edu
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  • T. E. Targett

    1. University of Delaware, School of Marine Science and Policy, 700 Pilottown Rd, Lewes, DE 19958, U.S.A.
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Author to whom correspondence should be addressed at present address: University of Delaware, Department of Civil and Environmental Engineering, 301 DuPont Hall, Newark, DE 19716, U.S.A. Tel.: +1 207 312 8752; fax: +1 302 831 8402; email: damian@udel.edu

Abstract

Swimming speed, angular correlation and expected displacement were measured in juvenile summer flounder Paralichthys dentatus acclimated to either oxygen saturation (c. 7·8 mg O2 l−1; saturation-acclimated fish) or diel-cycling hypoxia (cycling between 11·0 and 2·0 mg O2 l−1) for 10 days and subsequently exposed to more severe diel-cycling hypoxia (cycling between 7·0 and 0·4 mg O2 l−1). Saturation-acclimated P. dentatus exhibited an active response to declining dissolved oxygen (DO) by increasing swimming speed, angular correlation and expected displacement to peak levels at 1·4 mg O2 l−1 that were 3·5, 5·5 and 4·2 fold, respectively, greater than those at DO saturation. Diel-cycling hypoxia-acclimated P. dentatus also exhibited an active response to declining DO, although it was relatively less pronounced. Diel-cycling hypoxia-acclimated P. dentatus swimming speed, however, still doubled as DO decreased from 7·0 to 2·8 mg O2 l−1. Diel-cycling hypoxia-acclimated P. dentatus did not recover as well from low DO exposure as did saturation-acclimated fish. This was reflected in their relatively more random swimming (low angular correlation between successive moves) and poor maintenance of rank order between individuals during the recovery phase. Even saturation-acclimated P. dentatus did not resume swimming at speeds observed at saturation until DO was 4·2 mg O2 l−1. Paralichthys dentatus were very sensitive to decreasing DO, even at DO levels that were not lethal or growth limiting. This sensitivity and their poor recovery may preclude juvenile P. dentatus from using highly productive nursery habitats affected by diel-cycling hypoxia.

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