Ionic content of body fluids and sodium efflux in Oreochromis alcalicus grahami, a fish living at temperatures above 30°C and in conditions of extreme alkalinity

Abstract

1. Values for blood plasma ions at 35°C are: Na, 210.4 ± 4.6; Cl, 144.6 ± 2.6 and K, 6.5 ± 0.4 mM; osmotic pressure, 400 ± 18 mOsm. 2. 2. Blood ionic composition resembles that of marine teleost species except that at 210 mM plasma Na+ is rather elevated while body ionic composition is unusual in that at 46 mM kg− K+ is rather low. 3. 3. Although Lake Magadi has a high bicarbonate content (87 mM) and high alkalinity (pH 10) blood values for these parameters are not unusually high when compared to other fishes. 4. 4. O. alcalicus grahami shows a Na+ efflux value of only 5 mM kg− hr−1 at 35°C which is at least five times lower than values reported for marine teleosts and low branchial ionic permeability appears to be a major ionic regulatory adaptation to life in an alkaline environment