Eyeless Mexican cavefish save energy by eliminating the circadian rhythm in metabolism

PLoS One. 2014 Sep 24;9(9):e107877. doi: 10.1371/journal.pone.0107877. eCollection 2014.


The eyed surface form and eyeless cave form of the Mexican tetra Astyanax mexicanus experience stark differences in the daily periodicities of light, food and predation, factors which are likely to have a profound influence on metabolism. We measured the metabolic rate of Pachón cave and surface fish at a fixed swimming speed under light/dark and constant dark photoperiods. In constant darkness surface forms exhibited a circadian rhythm in metabolism with an increase in oxygen demand during the subjective daytime, whereas cave forms did not. The lack of circadian rhythm in metabolism leads to a 27% energy savings for Pachón cave fish compared to surface fish when comparing both forms in their natural photoperiods. When surface forms were tested under constant dark conditions they expended 38% more energy than cave forms under equivalent conditions. Elimination of the circadian rhythm in metabolism may be a general feature of animals that live in perpetually dark food-limited environments such as caves or the deep sea.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Basal Metabolism
  • Characidae / physiology*
  • Circadian Rhythm*
  • Darkness
  • Mexico
  • Ocular Physiological Phenomena
  • Photoperiod

Grant support

DM was supported by a Marie Curie Fellowship from the European Research Agency. RS was supported by an Erasmus Work Placement Grant. EW acknowledges the ongoing support of the Swedish Research Council. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.