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Front. Physiol. | doi: 10.3389/fphys.2018.01645

The air-breathing Macropodus opercularis differs from aquatic breathers in strategies to maintain energy homeostasis under hypoxic and thermal stresses

  • 1Marine Research Station, Institute of Cellular and Organismic Biology, Academia Sinica, Taiwan
  • 2Department of Life Science, Tunghai University, Taiwan

Two major strategies are used by most fish to maintain energy homeostasis under hypoxia. One is to utilize alternative metabolic pathways to increase energy production, and the other is to limit energy expenditure by suppressing energy-consuming processes, especially ionoregulation. Some anabantoid fishes live in tropical rivers, where hypoxic environments occur frequently. We previously found that under ambient hypoxia, anabantoid fishes do not downregulate Na+/K+-ATPase (NKA) activity to conserve energy in gills but instead increase the frequency of air-breathing respiration (ABR). In addition to the hypoxic condition, another factor that may cause cellular hypoxia in fish is abnormally high environmental temperatures. The frequency of such extreme thermal events has increased due to global climate change. In the present study, we examined whether the anabantoid fish, Macropodus opercularis employs the two strategies mentioned above to resist both ambient hypoxic and elevated thermal (cellular hypoxic) conditions. Results indicate that neither glucose metabolism nor gill NKA activity were altered by hypoxia, but glucose metabolism was increased by thermal stress. NH4+ excretion and ABR frequency were both increased under hypoxia, thermal or hypoxic-and-thermal treatments. In fish that were restricted from breathing air, increased mortality and glucose metabolism were observed under hypoxic or thermal treatments. These results suggest that for M. opercularis, increasing ABR is an important strategy for coping with unmet oxygen demand under hypoxic or thermal stress. This behavioral compensation allows anabanoid fish to physiologically withstand hypoxic and thermal stresses, and constitutes a mechanism of stress resistance that is unavailable to water-breathing fishes.

Keywords: Anabantoid fish, hyperthermia, hypoxia, Energy allocation, Energy Metabolism, Ionoregulation, air-breathing respiration

Received: 25 Jul 2018; Accepted: 31 Oct 2018.

Edited by:

Cheng-Hao Tang, National Sun Yat-sen University, Taiwan

Reviewed by:

Alexssandro G. Becker, Universidade Federal do Paraná, Setor Palotina, Brazil
Amit K. Sinha, University of Arkansas at Pine Bluff, United States  

Copyright: © 2018 Wang and Lin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Miss. Min-Chen Wang, Marine Research Station, Institute of Cellular and Organismic Biology, Academia Sinica, Taipei City, Taiwan, mcwinlab@gmail.com
Dr. Hui-Chen Lin, Department of Life Science, Tunghai University, Taichung City, 40704, Taiwan, hclin@thu.edu.tw