Arctic charr thrive at high densities and can live in freshwater year round, making this species especially suitable for inland, closed containment aquaculture. However, it is a cold water salmonid, which both limits where the species can be farmed and places wild populations at particular risk to climate change. Previously, we identified genes associated with tolerance and intolerance to acute, lethal temperature stress in Arctic charr. However, there remained a need to examine the genes involved in the stress response to more realistic temperatures that could be experienced during a summer heat wave in grow-out tanks that are not artificially cooled, or under natural conditions. Here, we exposed Arctic charr to sub-lethal heat stress of 15-18°C for 72 hours, and gill tissues extracted before, during (i.e., at 72 hrs), immediately after cooling and after 72 hours of recovery at ambient temperature (6°C) were used for gene expression profiling by microarray and qPCR analyses. The results revealed an expected pattern for heat shock protein (Hsp) expression, which was highest during heat exposure, with significantly reduced expression (approaching control levels) quickly thereafter. We also found that the expression of numerous ribosomal proteins was significantly elevated immediately and 72 hrs after cooling, suggesting that the gill tissues were undergoing ribosome biogenesis while recovering from damage caused by heat stress. We suggest that these are candidate gene targets for the future development of genetic markers for broodstock development or for monitoring temperature stress and recovery in wild or cultured conditions.