Submitted on July 27, 2006
Accepted on July 4, 2007
Multiple Strategies of Lake Victoria Cichlids to cope with Life Long Hypoxia include Hemoglobin Switching
H.A. Rutjes1, Maaike C Nieveen1, Roy E. Weber2, Frans Witte1, and Guido E.E.J.M. Van den Thillart1*
1 Biology, Leiden University, Leiden, Netherlands
2 Zoophysiology, University of Aarhus, Aarhus, Denmark
* To whom correspondence should be addressed. E-mail: g.van.den.thillart{at}biology.leidenuniv.nl.
Many fish species adapt to hypoxia by reducing their metabolic rate and increasing Hb-O2 affinity. Pilot studies with young brood of cichlids showed that the young could survive severe hypoxia in contrast to 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 (80-90% air saturation) or hypoxia (10% air saturation). Muscle tissue of the adults was analyzed for glycogen, lactate dehydrogenase, and citrate synthase. Blood was analyzed for hematocrit, hemoglobin composition, and intra-erythrocytic levels of ATP and GTP (guanosine triphosphate). Hemoglobin and hematocrit levels were significantly higher in all hypoxia-raised fish of the three species, reflecting a physiological adaptation to safeguard oxygen transport capacity. In hypoxia-raised tilapia, intra-erythrocytic GTP levels were decreased, suggesting an adaptive increase of blood oxygen affinity. Similar changes were not found in hypoxia-raised H. ishmaeli. In this species, however, all hypoxia-raised specimens exhibited a distinctly different iso-hemoglobin pattern compared to their normoxia-raised siblings, which correlated with a higher intrinsic hemoglobin-O2 affinity in the former. All hypoxia raised cichlids showed a left shifted hemoglobin dissociation curve by either allosteric control or - in H. ishmaeli - by the production of new hemoglobins. It is concluded that the adaptation to life long hypoxia is mainly due to improved oxygen transport.
