This presentation addresses the role of mitochondria in non-genetic inheritance, shaping the adaptive potential of populations under a warming ocean scenario. In our study, we investigated transgenerational plasticity (TGP) to partition the relative contribution of maternal vs. paternal (additive genetic) effects to offspring body size (a key component of fitness). We investigated the potential physiological mechanisms underlying whole-organism growth/size responses by analysing mitochondrial capacities in the offspring of differently acclimated parental groups. Offspring body size of marine sticklebacks benefited from maternal TGP and were larger when reared at the respective mother’s acclimation temperature. This points at an involvement of mitochondrial metabolism, as in fish, mitochondria are almost exclusively inherited maternally. Indeed, mitochondrial capacities were significantly influenced by maternal temperature, reflecting the observed growth patterns and thus linking offspring body size to maternal inheritance of mitochondria. Maximum mitochondrial capacities differed depending on maternal temperature and offspring of warm acclimated mothers that were reared at warm temperatures showed full metabolic compensation with respect to heart mitochondrial capacities in comparison to the control groups. Our results for mitochondrial capacities between the different offspring groups suggest that mitochondria are a primary target for non-genetic transgenerational thermal compensation of metabolic rates in a changing climate, as an optimized energy metabolism will generate a higher scope for growth. Warm acclimated mothers adjust the metabolism of mitochondria that are inherited by offspring, and differences in mitochondrial capacities and efficiency underlie the differences observed in offspring growth.