Respiration in An Air-Breathing Fish, the Climbing Perch, Anabas Testudineus

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Abstract
1. A study has been made of the patterns of respiration in climbing perch (Anabas testudineus) living in water containing different concentrations of oxygen and carbon dioxide and also in air-exposed fish. 2. The fish breathes both water and air in normal tap water. The intervals between air-breaths are irregular and vary within the range 8-15 min. 3. Air-breathing increases in water of high CO2 content. The time interval between air breaths falls with increasing CO2 content. Gill ventilatory frequency increases when 5-10% CO2 is bubbled into the water. Aquatic respiration stops and only aerial respiration occurs if more than 20% CO2 is bubbled into the water. 4. Three factors, CO2 content, pH and O2 content of water, control the respiratory patterns in climbing perch. Of these CO2 content appears to be most important for fish living in water. 5. The climbing perch can live for long periods (6-12 h during observations made) in water of very high CO2 content (20-33 vols. %). In such hypercarbic water gases are only exchanged through the air-breathing organs. The mouth and opercula are closed tightly and gill ventilation stops completely. 6. Exposure to air increases air-breathing but the frequencies are irregular. Inhalation of hypoxic gas or pure nitrogen also evokes air-breathing.