Early‐Life Heat Stress Impairs Cognition and Alters Its Covariation With Behaviour in Zebrafish

As global temperatures rise, animals are increasingly exposed to heat stress, with growing evidence suggesting that such stress can impair cognitive functions. While research has documented these cognitive effects in adult mammals, birds and fish, less is known about the consequences of thermal stress during early development. Here, we investigated the effects of short‐term heat stress on learning in zebrafish ( Danio rerio ). Embryos were exposed to elevated temperatures (+5°C) for 2 days, beginning 10 days after fertilisation, and tested for learning performance 2 days post‐treatment. Heat‐stressed individuals showed reduced learning ability compared to controls. Furthermore, heat stress affected the covariation between learning and behavioural responses: in the group exposed to heat stress, individuals with stronger responses to stimulation learned faster, a relationship absent in control subjects. These results suggest that heat stress not only impairs cognitive performance but also alters the structure of behavioural‐cognitive trait associations. Given the ecological importance of cognition for survival and fitness, such changes may have far‐reaching consequences for wild populations.