Cognitive abilities in animals are a focal topic in contemporary behavioral ecology and comparative psychology. As the only vertebrate clade fully adapted to aquatic environments, fishes display distinctive adaptations in perception, information processing, and behavioral decision-making. The aquatic habitats on which they depend differ markedly from terrestrial systems in physical structure, light regimes, chemical cues, and ecological pressures; these contrasts have shaped fishes’ unique cognitive traits and behavioral strategies. A systematic understanding of fishes’ cognitive performance and the behavioral–ecological mechanisms underlying it not only elucidates the evolutionary trajectories and adaptive significance of animal cognition, but also provides theoretical and applied guidance for sustainable fisheries management, the optimization of aquaculture practices, improvements in the welfare of farmed fish, and engagement with related ethical considerations. This review synthesizes research on fish cognition, with an emphasis on advances in four domains—learning and memory, spatial cognition, perceptual discrimination, and social cognition. We further summarize commonly used experimental paradigms and methodological approaches in studies of fish cognition and, on this basis, critically assess the limitations and challenges of prior work as well as priorities for future research. Our aim is to deepen the theoretical understanding of fish cognition and broaden its practical applications in aquaculture and fisheries ecosystem management.