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The ability of populations to adapt to environmental change and the spatial scale at which this adaptation occurs are fundamentally important issues in evolutionary biology, and ones that may benefit greatly from the study of genetic variability in reaction norms, which represent the plasticity of phenotypic traits across an environmental gradient. Therefore variable reaction norms can reflect genetic differences in the ability of individuals, families, populations, and species to respond to natural and anthropogenic environmental change. Fishes are ideal organisms in which to study plasticity because of their remarkable intraspecific morphological, physiological, behavioural, and life history variation. Here, we review studies demonstrating genetic variability in reaction norms in fishes. Genetic variability in plasticity among full- and half-sib families suggests potential for some populations to develop an adaptive norm of reaction (recalling that plasticity need not be adaptive). Reaction norm variability among populations suggests that adaptive genetic divergence can occur rapidly when selection pressures are strong and that the spatial scale of adaptation is much smaller than previously believed for some species with high dispersal capabilities. These studies demonstrate the potential of using reaction norms to study the evolution of novel phenotypes and the influence of temporal environmental variability and gene flow on the evolution of phenotypic plasticity, which can then be used to predict how populations will respond to directional environmental change. To promote future research into genetic variability in reaction norms, we propose questions that would benefit from such an approach and discuss some important considerations for designing experiments to investigate questions related to genetic variation in plasticity and phenotypic evolution. Key words: phenotypic plasticity, genotype-environment interaction, adaptation, environmental change. La capacite d'adaptation au changement environnemental et l'echelle spatiale a laquelle cette adaptation survient, constituent des defis d'importance fondamentale en biologie evolutive, un sujet qui pourrait beneficier grandement de l'etude de la variabilite des normes de reaction. Les normes de reaction representent la plasticite des traits phenotypiques le long d'un gradient environnemental. Consequemment, des normes de reaction variables peuvent refleter des differences genetiques dans la capacite des individus, des familles, des populations et des especes a reagir au changement environnemental naturel et anthropogene. Les poissons constituent des organismes ideaux pour l'etude de la plasticite compte tenu de la variation intraspecifique remarquable de leur morphologie, de leur physiologie, de leur comportement et de leur cycle de vie. Les auteurs passent en revue les etudes demontrant la variabilite genetique des normes de reaction chez les poissons. La variabilite de la plasticite parmi les familles biparentales ou mono parentales suggere la capacite de certaines populations a developper une norme de reaction adaptative (en se rappelant que la plasticite ne doit pas necessairement etre adaptative). La variabilite des normes de reaction parmi les populations suggere qu'une divergence genetique adaptative peut se manifester rapidement, lorsque les pressions de selection sont fortes et que l'echelle spatiale d'adaptation est beaucoup plus petite qu'on le croyait, chez certaines especes ayant de fortes capacites de dispersion. Ces etudes demontrent que le potentiel de l'utilisation des normes de reaction pour etudier l'evolution de nouveaux phenotypes et l'influence de la variabilite temporelle environnementale ainsi que flux de genes sur l'evolution de la plasticite phenotypique, lesquels peuvent alors etre utilises pour predire comment les populations repondront au changement environnemental directionnel. Pour promouvoir des recherches futures sur la variabilite genetique des normes de reaction, les auteurs proposent quelques questions qui beneficieraient d'une telle approche, et discutent quelques considerations importantes pour concevoir des experiences soulevant des questions reliees a la variation genetique de la plasticite de l'evolution phenotypique. [Traduit par la Redaction] Mots-cles: plasticite phenotypique, interaction genotype environnement, adaptation, changement environnemental., Introduction The ability of individuals or populations to respond to environmental change is integral to species persistence. If a fitness-related trait is optimally expressed in specific environmental conditions, then a [...]