It is generally agreed that much of variation in gene expression in response to a particular environmental condition has a heritable genetic basis and ultimately, combined with extensive expression variability, it provides the substrate for evolution. Notothenioids, perciform fish living in Antarctic waters, are highly stenotherm organisms and offer a truly unique opportunity to study what characteristics of gene expression levels and pool of expressed genes (the pool of messenger RNAs, mRNA, is called the transcriptome) are behind the differences between stenothems and eurytherms, as a result of the evolution of temperature preference. Studying these fish could help to directly identify the transcriptomic basis of temperature-related evolutionary adaptation by comparing species living in thermally distinct habitats to their most phylogenetically basal relative. In this proposal, three target notothenioid species will be taken into account: two extreme stenotherms adapted to polar conditions, Notothenia rossii and Champsocephalus gunnari and the subpolar eurytherm Eleginops maclovinus. This proposal is aimed at verifying if the evolutionary adaptation to a specific temperature, causes any difference in expression levels at a common set of genes. The modern methodology adopted, the transcriptome sequencing (Illumina RNA-Seq) and the quantitative RT-PCR (OpenArray system) are aimed at collecting and validating a dataset of gene expression rates as broad as possible. Expression of genes hypothetically involved in the temperature adaptation will be also studied in different body tissues, after short and long term exposure to a temperature higher than natural. The likely reduction in available habitats due to global warming and their high specialization to low temperature makes notothenioids hypothetically more vulnerable and potentially genetically compromised in their abilities to acclimate to rising water temperatures and for this reason a hot target for conservation.