Rainbow trout (Oncorhynchus mykiss) is a fish that is particularly sensitive to changes in water quality. Global warming is expected to increase the frequency and intensity of heatwaves, resulting in more common combined acute hyperthermia and hypoxia conditions in fish farms (Reid et al., 2019). Such poor thermal and oxygenation conditions induce problems including growth losses, increased mortality and pathogens pressure. However, genetic selection to breed more robust fish is an interesting option to improve fish tolerance to non-optimal water quality (Vandeputte and Prunet, 2002). Some research studies have already highlighted the potential of genetic selection for acute hypoxia and temperature resistance traits in fish (Chen et al., 2015; Ineno et al., 2005; Prchal et al., Unpublished data). In order to improve our understanding of the genetic architecture of these two traits, we used six isogenic rainbow trout lines. Within a line, all fish have the same genotype and preliminary tests revealed contrasting levels of resistance to hypoxia and temperature between lines. Using this research model, the objectives of the study were to: i) confirm the existence of genetic variability for resistance to hypoxia and high temperature; ii) investigate the ranking stability of genotypes at different ages for hyperthermia and hypoxia resistance traits, which is an essential information to determine the stage at which fish should be phenotyped in a breeding program; iii) determinate the relationship between hyperthermia resistance and hypoxia resistance