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Am J Physiol Regul Integr Comp Physiol 293: R1376-R1383, 2007. First published July 11, 2007; doi:10.1152/ajpregu.00536.2006
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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Multiple strategies of Lake Victoria cichlids to cope with lifelong hypoxia include hemoglobin switching

H. A. Rutjes,1 M. C. Nieveen,1 R. E. Weber,2 F. Witte,1 and G. E. E. J. M. Van den Thillart1

1Institute of Biology, Leiden University, Leiden, The Netherlands; and 2Zoophysiology, Department of Biological Sciences, University of Aarhus, Aarhus, Denmark

Submitted 27 July 2006 ; accepted in final form 4 July 2007

Many fish species adapt to hypoxia by reducing their metabolic rate and increasing hemoglobin-oxygen (Hb-O2) affinity. Pilot studies with young broods of cichlids showed that the young could survive severe hypoxia in contrast with the adults. It was therefore hypothesized that early exposure results in improved oxygen transport. This hypothesis was tested using split brood experiments. Broods of Astatoreochromis alluaudi, Haplochromis ishmaeli, and a tilapia hybrid (Oreochromis) were raised either under normoxia (NR; 80–90% air saturation) or hypoxia (HR; 10% air saturation). The activity of the mitochondrial citrate synthase was not different between NR and HR tilapia, but was significantly decreased in HR A. alluaudi and H. ishmaeli, indicating lowered maximum aerobic capacities. On the other hand, hemoglobin and hematocrit levels were significantly higher in all HR fish of the three species, reflecting a physiological adaptation to safeguard oxygen transport capacity. In HR tilapia, intraerythrocytic GTP levels were decreased, suggesting an adaptive increase of blood-O2 affinity. Similar changes were not found in HR H. ishmaeli. In this species, however, all HR specimens exhibited a distinctly different iso-Hb pattern compared with their NR siblings, which correlated with a higher intrinsic Hb-O2 affinity in the former. All HR cichlids thus reveal left-shifted Hb-O2 equilibrium curves, mediated by either decreased allosteric interaction or, in H. ishmaeli, by the production of new hemoglobins. It is concluded that the adaptation to lifelong hypoxia is mainly due to improved oxygen transport.

hypoxia acclimation; isohemoglobins; P50; phenotypic plasticity; oxygen transport


Address for reprint requests and other correspondence: G. Van den Thillart, Institute Biology Leiden, POB 9516, 2300RA, Leiden, The Netherlands (e-mail: g.van.den.thillart{at}biology.leidenuniv.nl)






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