Climate change is impacting temperatures globally, altering the frequency, intensity, and extent of extreme events such as heatwaves and droughts. This modification poses a challenge to biodiversity worldwide and presents a particular threat to tropical biota, which already reside close to their thermal maxima. Fish play a crucial role in the diet of the Amazon, particularly for traditional communities that rely on them as their primary protein source. The Amazon boasts the largest diversity of freshwater fish globally, each exhibiting numerous physiological and behavioural adaptations to thrive in the warm and often hypoxic waters of the Amazon. Comprehending how rising temperatures affect Amazonian fish species is essential for policymakers tasked with crafting strategies to safeguard the bio and sociodiversity of the Amazon. Faced with increasing temperatures, fish respond by adjusting their physiology and behaviour until they reach their thermal limit. Traditional thermal tolerance tests conventionally use the loss of equilibrium as the final endpoint for determining thermal limits. However, well before this loss of equilibrium, fish undergo physiological and behavioural adjustments to cope with the changing conditions. Monitoring behavioural changes during critical thermal tolerance tests provides insights into how fish utilise physiological and behavioural adaptations in this progressively warmer environment. We will elucidate behavioural changes observed during thermal tolerance tests of various Amazonian species and explore their connection to physiological adaptations to the Amazonian environment. Additionally, we will consider how these changes can serve as early warning signs of thermal vulnerability for fish species.