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Journal of Experimental Biology 151,361-369 (1990)
Published by Company of Biologists 1990

The Effects of Reducing Water pH and Total CO₂ on a Teleost Fish Adapted to an Extremely Alkaline Environment

P. A. WRIGHT ¹, S. F. PERRY ², D. J. RANDALL ³, C. M. WOOD ⁴, and H. BERGMAN ⁵

¹ Department of Animal Physiology, Veterinary College, University of Nairobi, Kenya; Laboratory of Kidney and Electrolyte Metabolism, National Institutes of Health, Building 10 Room 6N307 Bethesda, MD 20892 USA
² Department of Animal Physiology, Veterinary College, University of Nairobi, Kenya; Department of Biology, University of Ottawa Ottawa, Ontario, Canada, KIN 6N5
³ Department of Animal Physiology, Veterinary College, University of Nairobi, Kenya; Department of Zoology, University of British Columbia Vancouver, BC, Canada V6T 2A9
⁴ Department of Animal Physiology, Veterinary College, University of Nairobi, Kenya; Department of Biology, McMaster University Ontario, Canada, L8S 4K1
⁵ Department of Animal Physiology, Veterinary College, University of Nairobi, Kenya; Department of Zoology and Physiology, University of Wyoming Laramie WY 82071, USA

The teleost fish Oreochromis alcalicus grahami is well adapted to an extremely alkaline environment (pHIO, total CO₂ 184mmoH^-1) in Lake Magadi, Kenya. O. a. grahami excretes all nitrogenous wastes as urea, and exposure to neutral water (pH7, total CO₂>lmmoll^-1 ) results in a complete inhibition of urea excretion. In the present study, we further characterized the physiological effects of transferring O. a. grahami from alkaline to neutral water. Exposure to neutral water resulted in a significant decrease in blood pH, a large reduction in plasma HCO₃^- levels, a severe impairment of swimming ability, an increase in Na^+; influx, but no change in O₂ consumption. A closely related species of tilapia, O.nilodca, living in neutral waters of the Sagana River, was relatively unaffected by acute exposure to tapwater at pH 10, but showed a marked alkalosis in Lake Magadi water prior to death. These results demonstrate that O. a. grahami thrive in an environment of high pH and bicarbonate/carbonate concentration, conditions that are fatal to other species adapted to neutrality. O. a. grahami, however, is extremely unusual amongst aquatic animals in its adverse response to neutral water.

Key words: urea excretion, ammonia excretion, swimming speed, Lake Magadi, soda lake

Accepted on February 20, 1990

This article has been cited by other articles:

				P. Walsh, M Grosell, G. Goss, H. Bergman, A. Bergman, P Wilson, P Laurent, S. Alper, C. Smith, C Kamunde, et al. Physiological and molecular characterization of urea transport by the gills of the Lake Magadi tilapia (Alcolapia grahami) J. Exp. Biol., January 2, 2001; 204(3): 509 - 520. [Abstract] [PDF]