Studies on the Queensland lungfish, Neoceratodus forsteri (Krefft). 3. Aerial respiration in relation to habits.

Abstract

Field observations made on the Mary and Burnett rivers in Queensland show that seasonal stagnancy and deoxygenation are unlikely to be factors accounting for the air-breathing habit in Neoceratodus, as current theory suggests. An alternative hypothesis that the lung is an accessory respiratory organ during active periods, was suggested by current work which showed that Neoceratodus is more active nocturnally and surfaces to take air more often at night. Respirometry studies on juvenile fish confirmed this, for the oxygen consumption of forcibly active fish prevented from surfacing while in the respirometer, was consistently lower than that of fish allowed to surface. At 25°C, active fish allowed to surface had an oxygen consumption of 0.07 ml g-l hr-l, derived from branchial respiration at a rate of 67 beats/min supplemented by use of the lung. When prevented from surfacing however the oxygen consumption fell to approximately 0.05 ml g-l hr-1, derived from gills alone, but with a branchial pumping rate of 80 beats/min. This correlation of oxygen consumption with branchial pumping emphasizes the limit placed on the fish by its gills, whereas the higher oxygen consumption exhibited by active fish allowed to surface indicates the value of the lung as an accessory respiratory organ, allowing more vigorous reaction to a stimulus than would be possible with gills only.