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Oxygen consumption in weakly electric Neotropical fishes


Weakly electric gymnotiform fishes with wave-type electric organ discharge (EOD) are less hypoxia-tolerant and are less likely to be found in hypoxic habitats than weakly electric gymnotiforms with pulse-type EOD, suggesting that differences in metabolism resulting from EOD type affects habitat choice. Although gymnotiform fishes are common in most Neotropical freshwaters and represent the dominant vertebrates in some habitats, the metabolic rates of these unique fishes have never been determined. In this study, O2 consumption rates during EOD generation are reported for 34 gymnotiforms representing 23 species, all five families and 17 (59%) of the 28 genera. Over the size range sampled (0.4 g to 125 g), O2 consumption of gymnotiform fishes was dependent on body mass, as expected, fitting a power function with a scaling exponent of 0.74, but the O2 consumption rate was generally about 50% of that expected by extrapolation of temperate teleost metabolic rates to a similar ambient temperature (26°C). O2 consumption rate was not dependent on EOD type, but maintenance of “scan swimming” (continuous forwards and backwards swimming), which is characteristic only of gymnotiforms with wave-type EODs, increased O2 consumption 2.83±0.49-fold (mean±SD). This suggests that the increased metabolic cost of scan swimming could restrict gymnotiforms with wave-type EODs from hypoxic habitats.

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The authors would like to thank Hernan Ortega and Lorgio Verdi for helping to arrange permits to work in the Peruvian Amazon, Katty Miche for field assistance, Victoriano Panduro of the Red Tail Cat Aquarium in Iquitos, Peru for providing space to perform experiments, and Lauren J. Chapman, David H. Evans, Brian K. McNab, and Ashley W. Seifert for valuable insights and discussions. The final manuscript was greatly improved by comments from Philip Stoddard and an anonymous reviewer. All studies were approved by the University of Florida Institutional Animal Care and Use Committee, and by the Peruvian National Ministry of the Environment under permit 13 S/C-2000 INRENA-DGANPFS-DANP to J.S. Albert.

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Correspondence to David Julian.

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Julian, D., Crampton, W.G.R., Wohlgemuth, S.E. et al. Oxygen consumption in weakly electric Neotropical fishes. Oecologia 137, 502–511 (2003).

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  • Gymnotiforms
  • Electric fish
  • Electric organ discharge
  • Metabolism
  • Amazon
  • Scan swimming