The thermal sensitivity of mitochondrial function was investigated in the stenothermal Antarctic ®sh Lepidonotothen nudifrons. State 3 respiration increases with increasing temperature between 0°C and 18°C with a Q 10 of 2.43±2.63. State 4 respiration in the presence of oligomycin, an inhibitor of mitochondrial ATP synthase, quanti®es the leakage of protons through the inner mitochondrial membrane, which causes oxygen consumption without concomitant ATP production. This parameter shows an unusually high Q 10 of 4.21 0.42 (0±18°C), which indicates that proton leakage does not depend merely on ion diusion but is an enzyme-catalysed process. The dierential thermal sensitivity of oxidative phosphorylation (=state 3) and proton leakage (=state 4 in the presence of oligomycin) leads to progressive uncoupling of the mitochondria and decreased eciency of oxidative phosphorylation under in vivo conditions if the body temperature of L. nudifrons increases.

Nearly all decapod crustaceans found in Antarctic waters south of the Antarctic Convergence are caridean shrimps (Natantia) while the group of Reptantia is largely absent in this area. Progress in the development of a physiological hypothesis is reported, which explains this distribution pattern based on differences in the regulation of magnesium levels in the haemolymph (

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Temperature-dependent adjustments of intracellular pH are thought to play a major role in the maintenance of protein function. Comparative studies were carried out in two species from the same ®sh family (Zoarcidae), the stenothermal Antarctic eelpout (Pachycara brachycephalum) and the eurythermal eelpout (Zoarces viviparus), to ®nd out whether pH regulation is modi®ed by temperature in the closely related species and to what extent the respective pattern diers between eurytherms and stenotherms. Previous invasive studies had compared individual animals sampled at various temperatures and suggested that a decrease in intracellular pH (pHi) values occurs at rising temperatures, as predicted by the alpha-stat hypothesis of acidbase regulation. The present study used non-invasive in vivo 31 P-NMR spectroscopy in non-anaesthetized, unrestrained ®sh for long-term online recordings in individual specimens. Control spectra obtained at T=0°C for P. brachycephalum and at 12°C for Z. viviparus indicated low stress conditions, as well as a high stability of energy and acid-base status over time periods longer than 1 week. Temperature changes had no in¯uence on the concentration of high-energy phosphates like phosphocreatine or ATP. Temperature-induced pH changes were monitored continuously in a range between 0 and 6°C for polar, and 12 and 18°C for temperate eelpout. A pHi change of around ±0.015 pH units/°C was observed within both species, in accordance with the alpha-stat hypothesis; however, extrapolation to the same temperature revealed dierent set points of pH regulation in the two species. These ®ndings con®rm that an alphastat pattern of pH regulation can be found in stenothermal Antarctic animals, at set points deviating from an alpha-stat pattern, however, in a between-species comparison.