RESPIRATORY BEHAVIOR, OXYGEN-CONSUMPTION AND RELATIVE DEPENDENCE ON AERIAL RESPIRATION IN THE AFRICAN LUNGFISH (PROTOPTERUS-ANNECTENS, OWEN) AND AN AIR-BREATHING TELEOST (CLARIAS-LAZERA, C.)

The relative dependence on branchial and pulmonary organs was studied in the African lungfish P. annectens and in the catfish Clarias lazera. The frequency of pulmonary ventilation varied, in the normal state, with the activity and age of the fish and followed a circadian rhythm. Small specimens of both species exhibited a higher branchial ventilatory rate than older specimens and depended largely on aquatic O2 uptake (over 85% and 90% in Clarias and Protopterus respectively). The dependence on aerial respiration appeared to develop gradually with age in Clarias but occurred over a limited age-range (200-300 g) in Protopterus. In mature fish (over 400 g), pulmonary respiration constituted 50-60% of the total in Clarias and 80-85% in Protopterus. Partitioning of O2 uptake between air and water depended on the O2 content of the water and that of O2 and CO2 in the pulmonary organs. Protopterus and Clarias surfaced for air when the O2 content of the respiratory organs was reduced to 90% and 85% (of that immediately following an air-breath) respectively. An increase in the pulmonary O2 content lengthened the apnoeic period and reduced pulmonary respiration more markedly in Protopterus than in Clarias whereas an increase of that of CO2 produced the reverse effects. © 1979 Dr. W. Junk b.v. Publishers.