As the oceans are warming, fish stocks are moving with the water masses of their preferred temperatures to stay within a physiologically optimal temperature range, provided further factors such as food availability and competition with other species allow for that. This has already been documented for several fish species of the North Sea, which have been moving northward at a rate of about 10 km per decade. In response to this warming trend, the North Arctic stock of Atlantic cod (Gadus morhua) has also shifted spawning areas to the north and expanded its range into the Barents Sea. For the greatest part of the year, juvenile Atlantic cod are now frequently found in the coastal waters of Spitsbergen, with an as yet unclear outcome for the ecosystems species composition. Ocean acidification is an additional stressor developing in parallel to ongoing climate warming. Future impacts of ocean acidification on organisms and ecosystems are expected to be greatest in cold regions, owing to enhanced CO2 solubility in cold waters and body fluids and to the concomitant exposure of organisms to a strong warming trend. At the same time, thermal tolerance windows are narrower and thus sensitivities to combined stressor effects are likely to be higher in cold-adapted polar compared to temperate species. The expected rise in carbon dioxide concentrations and temperature in the oceans (800-1000 µatm and 1-2 °C, respectively, until the year 2100) may thus prove to be particularly threatening to Boreal and Arctic ecosystems. Some of the commercially most important fish species in the North Atlantic belong to the family of Gadidae, namely Atlantic cod, haddock, pollock, whiting, and Polar cod, and have been the target of substantial industrial fishery in the Arctic. The Atlantic cod is now the subject of intensive aquaculture in Norway. Any shift in the population structure, caused by ocean acidification and warming (OAW) could thus have far reaching effects not only on the ecosystem itself but also on fisheries, and further, on aquaculture. The socio–economic consequences of such scenarios have not yet been evaluated. Within the German ocean acidification research programme BIOACID (2012-2015) we investigate how the combined effects of OAW affect different life stages and interactions between polar gadoid fish species and their prey. Objectives include addressing the question whether OAW affects interacting species differently due to divergent physiological optima and ranges, expressed in thermal tolerance windows and associated performance capacities and phenologies of specific life stages. We aim to identify fundamental mechanisms by unravelling the connections between levels of biological organisation, from genomic, molecular to cellular, individual and population level. Scopes for acclimation (physiology and behaviour) and adaptation (evolution) that together define species resilience are studied in various life stages (eggs, larvae, juveniles, adults) to identify the most sensitive one(s). We feed these data into socio-economic models to assess stock sensitivity and resilience to evaluate the possible consequences for fishery, aquaculture and last but not least, society.