| Zusammenfassung: | Dissolved oxygen and carbon dioxide undergo daily cycles in the water hyacinth community inhabited by Pseudobranchus striatus (Amphibia, Sirenidae). Concentrations of both gases are uniform from the surface to the bottom at sunrise, as is the water temperature. A slight temperature gradient of 1-2° C develops during the day, accompanied by an increasing top to bottom differential in the concentrations of the dissolved gases. This differential becomes maximal during the warmest part of the day, and disappears by the next morning. Oxygen peaks in the late afternoon, when carbon dioxide is at a minimum; oxygen is minimal at sunrise, when carbon dioxide is highest. At any given time, the oxygen concentration is lower under the hyacinths than it is in the open water and carbon dioxide is higher. Pseudobranchus can utilize purely aquatic respiration, or supplement this with air breathing. Analysis of field and experimental data suggests that supplemental air-breathing is required at least 50% of the day for the period studied.
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