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Physiological protective action of dissolved organic carbon on ion regulation and nitrogenous waste excretion of zebrafish (Danio rerio) exposed to low pH in ion-poor water

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Abstract

Dissolved organic carbon (DOC) represents a heterogeneous group of naturally-occurring molecules in aquatic environments, and recent studies have evidenced that optically dark DOCs can exert some positive effects on ionoregulatory homeostasis of aquatic organisms in acidic waters. We investigated the effects of Luther Marsh DOC, a dark allochthonous DOC, on ion regulation and N-waste excretion of zebrafish acutely exposed to either neutral or low pH in ion-poor water. In the first experiment, simultaneous exposure to pH 4.0 and DOC greatly attenuated the stimulation of Na+ diffusive losses (J Naout ), and prevented the blockade of Na+ uptake (J Nain ) seen in zebrafish exposed to pH 4.0 alone, resulting in much smaller disturbances in Na+ net losses (J Nanet ). DOC also attenuated the stimulation of net Cl losses (J Clnet ) and ammonia excretion (J Ammnet ) during acidic challenge. In the second experiment, zebrafish acclimated to DOC displayed similar regulation of J Nain and J Naout , and, therefore, reduced J Nanet at pH 4.0, effects which persisted even when DOC was no longer present. Protective effects of prior acclimation to DOC on J Clnet and J Ammnet at pH 4.0 also occurred, but were less marked than those on Na+ balance. Urea fluxes were unaffected by the experimental treatments. Overall, these effects were clearly beneficial to the ionoregulatory homeostasis of zebrafish at low pH, and were quite similar to those seen in a recent parallel study using darker DOC from the upper Rio Negro. This suggests that dark allochthonous DOCs share some chemical properties that render fish tolerant to ionoregulatory disturbances during acidic challenge.

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Acknowledgements

Supported in Brazil by FAPEAM and CNPq through the INCT-ADAPTA Grant to ALV, and a Science Without Borders Program grant to ALV and CMW (CNPq Process Number: 401303/2014-4), and in Canada by Discovery grants to CMW and DSS from the Natural Sciences and Engineering Research Council of Canada (NSERC). CMW was supported by the Canada Research Chairs program and a visiting fellowship from the Science Without Borders Program (CNPq-Brazil), while RMD received a postdoctoral fellowship from the same program (CNPq Process Number: 151083/2013-4). ALV received a research fellowship from CNPq. Special thanks to Linda Diao for technical assistance during the experiments.

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Correspondence to Rafael M. Duarte.

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Communicated by G. Heldmaier.

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Duarte, R.M., Wood, C.M., Val, A.L. et al. Physiological protective action of dissolved organic carbon on ion regulation and nitrogenous waste excretion of zebrafish (Danio rerio) exposed to low pH in ion-poor water. J Comp Physiol B 188, 793–807 (2018). https://doi.org/10.1007/s00360-018-1169-y

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  • DOI: https://doi.org/10.1007/s00360-018-1169-y

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