Camp. Biochem.P!z#oi. Vol. 81A, No. 2, PP. 423-426, 1985 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH Printed in Great Britain ~3~9429/ 85 $3.00 i_ 0.00 Q 1985 Pergamon Press Ltd THE OXYGEN UPTAKE OF SAROTHERODON NILOTICUS L. AND THE OXYGEN BINDING PROPERTIES OF ITS BLOOD AND HEMOLYSATE (PISCES: CICHLIDAE)” E. VERHEYEN,~ R. BLUST and C. DOUMEN Laboratory of Biochemistry and General Zoology, University of Antwerp (R.U.C.A.), Groenenborgerlaan 171, B 2020 Antwerp, Belgium. Telephone: (03) 2180347 zyxwvutsrqponmlkjihgf (Received 30 October 1984) zyxwvutsrqponmlkjihgfedcbaZYXWVUT Abstract-l. The oxygen consumption of Sarotherodon niloticus L. was found to decline below a critical oxygen concentration of about 2mg 0,/l. 2. An important influence of CO, on the oxygen affinity of whole blood was observed at all temperatures between 20 and 35°C for gas mixtures containing 5.6% CO,. 3. Purified hemolysate showed extremely high oxygen affinities (pso = 1.08 mmHg at pH 8.2 and 20°C). Low coo~rati~ty was observed at all temperatures from 20 to 35”C, and pH values between 6.5 and 8.2. 4. The Bohr effect proved to be important at pH values fower than pH 7.5 (Q = A logp,/A pH = -0.58 between pH 6.5 and 7.0 at 35°C). 5. The oxygen affinities show high thermal sensitivity without a marked pH influence (AH value for overall oxygenation at pH was -71.7 kJ/mol). 6. The obtained results are interpreted as adaptations to diurnal variations in ambient temperature and oxygen availability. INTRODUCTION The respiratory physiology of the aquatic fauna in African fresh water is very interesting because of the great diversity of habitats and respiratory properties of the water. Cichlids are mostly relatively small freshwater fish that are widely distributed in the tropical parts of the world. They display an enormous adaptive radiation in the large African lakes, but seem to have been somewhat less successful in fluviatile environments (Fryer and Iles, 1972). Most cichlids are known to show great tolerance to extreme variations in the physico-chemical properties of water, especially with regard to temperature, pH, salt concentrations and low oxygen levels. Surotherodon niloticus L., a mem- ber of the “Tilapia” group, is, wherever it occurs, larger than any other cichlid species present and is seemingly the dominant species of this group. Its success is due to an impressive plasticity in its ecology-related behaviour and growth pattern. In addition, this species developed a particularly good tolerance to high temperatures and low oxygen levels, which seems to be one of the main reasons for the extended range of this species and of its success as a food source inside and outside of Africa (Philippart and Ruwet, 1982; Lowe McConnei, 1958). This communi~tion reports our findings concern- ing the respiratory response of S’. niloticus to ambient oxygen levels and the respiratory properties of its whole blood and purified hemoglobin solutions. The obtained results are compared with character- istics previously found in mainly South American and Asian cichlids, in order to compare the respiratory - *This work is part of the program 2.9005.84 of the F.K.F.O. Y‘Bursaal” at the I.W.O.N.L. adaptations of these related species, which occur on four continents (Wilhelm and Weber, 1983). MATERIALS AND METHODS The Jish Live S. niloti~ were obtained from a Iocal commercial fish stock imported to Belgium (Tihange) by Philippart. The fish were kept in aerated aquaria at 25°C (Antwerp Zoo) and were fed every 48 hr with commercial fish food. Respiration measurements The respiration chamber consists of a sealed ghass cylinder (Fig. 1). Two respiration chambers are placed into a water- bath which has a matching number of sample taps (a) and three-way valves (b) mounted into the front panel. Each chamber opens by means of two orifices to the correspond- ing three-way valves and sample tap. The second outlet of the three-way valve connects through a waterproof circu- lation pump (Eheim 1012) (c) while the third outlet opens freely into the aerated and thermostated waterbath (d). By ma~p~ating the three-way valve, a constant waterflow of 4.5 l/min is created in this system, whether it is opened or closed. During the pm-experimental period of adaptation (20 hr) the test animals were provided with aerated filtered water by appropriately turning the three- way valve and opening the sample tap. During the experiments, the described respirometcr was used as a closed system. The rn~sur~~ts of the declining oxygen conce~~ation in the apparatus was continuously monitored with an oxygen-measuring electrode (f) (Delta Scientific 2110). From the obtained data (the decline in oxygen concen- tration as a function of time and oxygen concentration) the oxygen uptake &g Odgehr) was computed for 10 fish at 2.5% Unanaesthetized fish were bled by tail sectioning. The erythrocytes were washed three times in an ice-cold isotonic buffer (Tris-HCl 8.2) and lysed with the same buffer. To remove cellular debris the hemolysate was centrifuged at 423 CBPA 81/ ?-N