Respiratory Physiology of the Lake Magadi Tilapia (Oreochromis alcalicus grahami), a Fish Adapted to a Hot, Alkaline, and Frequently Hypoxic Environment
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Date
1996Author
Naraharal, Annie
Bergman, Harold L
Laurent, Pierre
Maina, JN
Walsh, Patrick J
Wood, Chris M
Type
ArticleLanguage
enMetadata
Show full item recordAbstract
The tilapia Oreochromis alcalicus grahami is a unique ureotelic teleost, the only
fish that lives in the alkaline hotsprings of Lake Magadi, Kenya. Physical condi-
tions and fish behavior were monitored in the Fish Springs Lagoon area, a site
where the tilapia were particularly abundant. Water Po2 and temperature fluc-
tuated more or less in parallel in a diurnal cycle from less than 20 Torr and less
than 25* C at night to greater than 400 Torr and 380 C during the day, whereas
pH remained constant at approximately 9.8. Field laboratory tests demonstrated
that routine Mo, (under normoxia) increased greatly from 270 C to 360 C (Qo
= 62) but then stabilized at a very high level (-~34.5 jgmol g-' h-1) up to the le-
thal temperature (- 42.5 " C), a pattern that was adaptive to the natural diurnal
regime. The Po2 threshold for survival during acute exposure (!; 1 h) was approx-
imately 16 Torr. Io, from water was well maintained down to a Po2 of 60 Torr,
below which it declined. Under such hypoxic conditions, the fish performed sup-
plementary surface breathing when allowed access to air. Both the better oxygen-
ated surface layer and air bubbles were inspired, resulting in significant uptake
of 02. The Po2 threshold for surface breathing was 1.8-fold higher at 3 7.50 C than at 310 C. Surface breathing and voluntary entry offish into air were observed in
the field. The blood O, dissociation curve at 300 -320 C was h3perbolic, with a
high afinity (P50o = 6 Torr), low cooperativity (Hill coeficient = 1. 18), and no
Bohr effect over the extracellularpH range 8.2-8.6.
URI
http://www.jstor.org/stable/30164249http://erepository.uonbi.ac.ke:8080/xmlui/handle/123456789/49584
Citation
Physiological Zoology, Vol. 69, No. 5 (Sep. - Oct., 1996), pp. 1114-1136Publisher
The University of Chicago Press Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071 Laboratoire de Morphologie Fonctionnelle et Ultrastructurale des Adaptations, Centre d'Ecologie et de Physiologie Energetique, CNRS, BP20CR, F-67037 Strasbourg cedex, France; Department of Veterinary Anatomy, University of Nairobi, Chiromo Campus