The crucian carp (Carassius carassius) manage to live without oxygen for months at low temperatures, and the only way to produce ATP is through the glycolytic pathway, which yields less than 10% of the ATP formed through aerobic metabolism. There are two options for compensating for the lowered ATP production efficiency; (1) increase the rate of ATP production and/or (2) reduce the rate of ATP consumption. An energy saving decrease of ion permeability (“channel arrest”) is displayed by the red-eared slider turtle (Trachemys scripta) during anoxia. To examine if a similar strategy is used by the crucian carp, brain mRNA levels of á-subunits of voltage-gated Na+ and Ca2+ (Nav and Cav) channels were quantified by real-time RT-PCR after exposure to 1-7 days of anoxia and anoxia followed by reoxygenation (all at 11°C). Heat shock proteins (Hsps) are known for protecting cells against detrimental effects of various stressors, including anoxia. Of the many functions proposed for Hsps, one is to refold proteins to their functional structure and another is to designate damaged proteins for degradation. In this thesis brain mRNA levels of Hsp90, Hsp70.1, Hsp70.2, Hsc70 and Hsp30 were quantified by real-time RT-PCR in crucian carp exposed to anoxia at two temperatures, 8°C and 13°C.No changes were found in mRNA levels of the á-subunits of the voltage-gated ion channels. Thus, the results do not support the “channel-arrest” hypothesis in crucian carp brain. By contrast, for Hsps a significant increase was found in both Hsp70.1 and Hsp70.2 mRNA levels at 13°C, while the response of these two paralogs showed divergent changes at 8°C. During anoxia, a decrease was found in Hsc70 and Hsp90 mRNA at 8°C, while at 13°C a significant decrease was found in Hsc70 and Hsp30 mRNA. These findings support the possibility that the Hsps are involved in the anoxia response of crucian carp brain, and that temperature has an effect on the regulation of some Hsps.