Respiration in a primitive air breather, amia calva

Abstract

Amia calva is a primitive air breathing fish having a well vascularized air bladder and efficient gills. The roles of aquatic and aerial gas exchange were studied in relation to temperature, activity and gas composition of the ambient water. At 10 °C, Amia is relatively inactive and is an almost exclusive water breather. With increasing temperature and activity, the rate of oxygen depletion from the air bladder increases progressively and the air breathing rate increases. At 30 °C, three times as much oxygen is taken from air as from water but the gills continue to be the principal site for CO 2 elimination. There was a gradual increase of air breathing and gill breathing rates with decreasing oxygen tensions in the water (Pw O 2 ) until the air breathing rate increased sharply and gill breathing declined at a Pw O 2 of 40 to 50 mm Hg at 20 °C. The sharply increased emphasis on air breathing occurred at higher oxygen tensions at 30 °C. The gill breathing rate varied reciprocally with air bladder O 2 tensions. The changes of gas tensions in central systemic vessels and vessels of the air bladder indicate a tendency for blood to bypass the exchange vessels in a gas exchange organ, either gill or air bladder, when it was not the primary site for oxygen uptake. The bimodal breathing pattern of Amia is discussed relative to the distribution and behavior of the fish.