Ongoing climate change and the related ocean warming as well as ocean acidification represent a major challenge for marine organisms. Marine fish are very efficient osmotic regulators, however, the details of the underlying compensation mechanisms remain to be explored, such as the interaction with elevated temperature. In the present study, effects on marine fish from ocean acidification and warming were investigated in long-term incubation experiments on Atlantic cod (Gadus morhua). Isolated perfused gill experiments were conducted to examine in vivo costs of the branchial energy budget and acid-base relevant ion transport under hypercapnia at optimum temperature (10 degree celsius) and in the warmth (18 degree celsius). In addition, potential effects on whole animal level as well as maximum enzyme capacities of central metabolic pathways in liver and muscle tissue were investigated. In conclusion, Gadus morhua possesses a wide range of compensational mechanisms on different systemic levels to cope with the challenge of ocean acidification, whereas high temperature has been confirmed as limiting factor.