Several animals are renowned for their cognitive skills, such as tool use, metacognition or social learning. However, it remains puzzling why some species excel whereas others - sometimes even closely related ones - do not. Archerfish show a remarkable assembly of skills in the context of their unique hunting behavior in which they down aerial prey with shots of water. Hoping to find ecological factors behind these skills, we have over the past years regularly traveled to archerfish mangrove habitats in Thailand (Figure 1A). One of our most consistent findings was the presence of other surface-feeding fish, particularly the similar-sized halfbeak Zenarchopterus buffonis, wherever we spotted groups of archerfish (Figure 1A; Supplemental movie S1). We describe here that Zenarchopterus is superbly equipped with water-wave detectors, rapidly detects the impact of prey even in the dark, is active at all times, is usually more numerous than archerfish and supplements its capabilities with visual skills. Without sophisticated additions to their hunting technique archerfish would thus lose most of their downed prey to halfbeaks. We suggest that the evolution of several skills of archerfish may have thus been influenced not only by intraspecific competition  but also by competition with other surface-feeding fish species.
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