The Antarctic ocean is a stable environment, especially concerning its constantly low temperatures that are not subjected to great seasonal changes. The resident animals are well adapted to a narrow temperature range and usually characterised as stenothermal, thus being vulnerable to temperature changes. This also accounts for the antarctic eelpout Pachycara brachycephalum, that has been studied in the course of this Bachelor-thesis for temperature-dependent long-term changes in acidbase- regulation and metabolism. Experiments were conducted on samples of white muscle tissue of animals that were previously incubated to six dfferent temperatures, ranging from -1 to 9°C, for two months. This range covers the known boundaries of temperature-tolerance of the species investigated. Changes in intracellular pH (pHi), c(CO2), [HCO3 -] and P(CO2) in white muscle tissue were determined using the homogenate technique. Through the analysis of 1H-NMR-spectra, I was able to look for changes in the relative concentrations of lactate, succinate and imidazole, in order to gain information on anaerobic metabolism and buffering characteristics of the cytoplasm. A decline in pHi of -0,018°C-1was detected between 0 and 3°C, that coincides with short-term studies on the same tissue and indicates alphastat regulation. pHi rose predominantly between 3 and 9°C; and an increased CO2-content was found between 7 and 9°C. These findings differ from previously investigated short-term patterns and indicate that alphastat regulation might not be sustainable on longer timescales. No change was found in the relative concentrations of anaerobic metabolites lactate and succinate, whilst the imidazole-concentration dropped already at 3°C and remained constantly low despite rising temperatures. The differences in pHi-regulation between long-term and acute adaptations could be related to the lack of this important intracellular buffer and to a rise in tissue bicarbonate concentration. The aerobic capacity of the animal is linked to its thermal tolerance. Earlier studies showed that oxygen supply is reduced at about 6°C resulting in negative growth rates at this temperature and above. Optimal growth has already been measured as well, ranging between 3 to 4°C and correlating with the lowest levels of gene-expression in hepatocytes. Up to these limits, pHi changed according to the proposed alphastat-Hypothesis. With increasing temperatures, first pHi, then CO2-content deviate from the alphastat-pattern and this corresponds to the before mentioned reduction in aerobic capacity. Therefore the capability to use aerobic metabolism seems to be defining the efficiency of acid-base regulation.