Size-selective harvesting common to fisheries is known to evolutionarily alter life-history and behavioural traits in exploited fish populations. Changes in these traits may in turn modify learning and decision-making abilities through energetic trade-offs with brain investment that can vary across development or via correlations with personality traits. We examined the hypothesis of size-selection-induced alteration of learning performance in three selection lines of zebrafish (Danio rerio) generated through intensive harvesting for large, small and random body-size for five generations followed by no further selection for ten generations that allowed examining evolutionarily fixed outcomes. We tested associative learning ability throughout ontogeny in fish groups using a colour-discrimination paradigm with a food reward, and the propensity to make group decisions in an associative task. All selection lines showed significant associative abilities that improved across ontogeny. The large-harvested line fish showed a significantly slower associative learning speed as subadults and adults than the controls. We found no evidence of memory decay as a function of size-selection. Decision-making speed did not vary across lines, but the large-harvested line made faster decisions during the probe trial. Collectively, our results show that size-selective harvesting evolutionarily alters associative and decision-making abilities in zebrafish, which could affect resource acquisition and survival in exploited fish populations.

Fish behaviour was video-recorded and manually scored for the variables listed in the dataset.