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Journal of Experimental Biology 55,421-434 (1971)
Published by Company of Biologists 1971

Respiration of an Air-Breathing Catfish Clarias Batrachus (Linn.)

B. N. SINGH ¹ and G. M. HUGHES ¹

¹ Research Unit for Comparative Animal Respiration, Bristol University, Bristol BSS 1UG

1. The respiratory behaviour and the rate of O₂ consumption and CO₂ elimination has been studied in Clarias batrachus under different environmental conditions which were also designed to test its suitability for life in water and on land.

2. The mean V O₂ from water and air is about 93 cc/kg/h. It consumes more O₂ from air (58.4%) than from water (41.6%). The rate of CO₂ release through the airbreathing organs is very low (RQ = 0.11), much more CO₂ is released through the gills and skin in water.

3. When the fish is submerged under air-saturated water and prevented from surfacing V O₂ is low (about 65 cc/kg/h). However, the fish does not struggle to breath air over a period of 6-8 h in aerated water. It exchanges about 17 % of O₂ through the skin and the rest through the gills in aerated water.

4. If the fish is maintained in still water in a closed chamber V O₂ is about 61 cc/kg/h. It starts to search for air once the O₂ tension in water is reduced below 100 mmHg and this searching becomes vigorous below 60 mmHg (WPO₂).

5. When exposed to air V _COCO2 is about 71 cc/kg/h; V O₂ air-exposed fish is about 37 cc/kg/h; hence RQ in air is only 0.52. It shows independent respiration in air although P_OO2 in ambient air was reduced to about 80 mmHg and P_COCO2 rose to about 51 mmHg.

6. When the fish is kept in deoxygenated water but allowed free access to air, V_OO2 is low, but RQ air is not reduced (0.51) from that of air-exposed fish. It shows dependent respiration under these conditions when aerial P_OO2 is reduced below 80 mmHg and P_COCO2 raised above 50 mmHg.

7. Clarias batrachus can live in deoxygenated water for several days if allowed free access to air, and appears to be more suited for life in poorly oxygenated water than Saccobranchus fossilis or Anabas testudineus.