Climate warming with associated heat waves presents a concerning challenge for ectotherms such as fishes. During heat waves, the ability to rapidly acclimate can be crucial for survival. However, surprisingly little is known about how different species and life stages vary in their acclimation dynamics, including the change in thermal tolerance through acclimation (i.e. acclimation capacity), the duration needed for the acclimation temperature to significantly alter thermal tolerance (i.e. acclimation response time), or the duration needed to achieve full acclimation (i.e. time to full acclimation). To shed light on this knowledge gap, we studied the acclimation dynamics of three wild-caught fishes (goldsinny wrasse, three-spined stickleback and European flounder) by assessing upper thermal tolerance (CTmax) after different periods of time acclimating to a warmed environment, and measured both CTmax and lower thermal tolerance (CTmin) in juvenile and adult lab-bred zebrafish acclimated to warmed or cooled environments. Thermal tolerance of zebrafish and sticklebacks significantly increased after a three hour exposure to a warm treatment, while this took six and 24 hours in wrasses and flounders, respectively. Goldsinny wrasse had the highest acclimation capacity, and did not reach full acclimation and stabilization of CTmax within the duration of the study. All other species fully acclimated between 4–10 days. Furthermore, juvenile zebrafish showed similar acclimation dynamics to adults for both upper and lower thermal tolerance, but had a higher CTmin for all acclimation durations. Our results demonstrate that acclimation dynamics vary across species, but may be similar between life stages within species. Understanding species-specific thermal plasticity is important for accurately modeling the projected impacts of climate change.