Respiratory properties of blood and pattern of gas exchange in the lungfish Neoceratodus forsteri (Krefft)

Abstract

Blood respiratory properties and gas exchange patterns have been studied in the lungfish Neoceratodus. O 2 - Hb dissociation curve reveals a high affinity for o 2 (P 50 of 11 mm Hg at P co 2 3.5 mm Hg). No Root effect but a pronounced Bohr effect was discernible. Temperature exerted only a minor influence on the affinity for O 2. The Co 2 dissociation curves conform to the shape observed in other classes of vertebrates and show a steep initial portion. The buffering capacity of the blood was low being 13.3 mMol/l/pH. An increased buffering power upon reduction of Hb was apparent. During rest in well oxygenated water, gill breathing prevailed entirely. Pulmonary arterial blood assumed to represent mixed arterial blood characteristically showed a Pco 2 averaging 3.5 mm Hg. Pao 2 was 40 mm Hg corresponding to an o 2 saturation of 95 %. The pulmonary venous blood showed gas partial pressures in equilibrium with those in pulmonary arterial blood and air, documenting the minor importance of the lung as a gas exchanger during these conditions. When the fish was artificially exposed to air P a o 2 diminished to 10–15 mm Hg with a concurrent increase in P a co 2 to 20 mm Hg in 30 min. While the lung performed well as an 02 absorber during air exposure it was totally inefficient in eliminating CO 2. The data indicate that Neoceratodus is unfit to live out of water for any length of time.