Phenotypic plasticity drives the development of laterality in the scale-eating cichlid fish <em>Perissodus microlepis</em>

Phenotypic plasticity, in which traits change in response to environmental conditions, is closely related to predator–prey interactions and speciation. The scale-eating cichlid fish Perissodus microlepis exhibits marked left–right differences in predatory behaviour and mouth morphology. While phenotypic plasticity is hypothesized to contribute to the formation of laterality, direct evidence remains scarce. We examined how plasticity shapes laterality by analysing the predatory behaviour and mandibular changes under different foraging conditions: picking granulated feed (non-scale-eating) and tearing scales from prey fish. During the predation experiment, the number of attacks increased over time. Behavioural analysis revealed that the mean inter-individual distance from scale-eater to prey gradually decreased, whereas mean swimming activity increased. Morphological analysis of the mandible showed elongation of the dentary bone along the anterior–posterior axis in the scale-eating groups..., The scale-eaters used in our study were bred in our laboratory with help of the World Freshwater Aquarium Aquatotto Gifu in Japan.&nbsp;We prepared three groups of specimens with different levels of scale-eating experience.&nbsp;The predation experiments were conducted daily for 127 days from the start, and predation was recorded every few days with a video camera; 32 videos of the Prey 1 group and 29 videos of the Prey 2 group were obtained.&nbsp;To detect the position of each scale-eating fish and prey fish in the tank, we fine-tuned the pre-trained neural network YOLO v3 on our dataset taken from the predation experiment.&nbsp;To assess the morphological features of the mouth of P. microlepis, we performed a geometric morphometric analysis on the lower jawbone. , # Data from: Phenotypic plasticity drives the development of laterality in the scale-eating cichlid fish *Perissodus microlepis* Dataset DOI: [10.5061/dryad.q83bk3jv8](10.5061/dryad.q83bk3jv8) ## Description of the data and file structure The scale-eaters used in our study were bred in our laboratory with the help of the World Freshwater Aquarium Aquatotto Gifu in Japan. We prepared three groups of specimens with different levels of scale-eating experience. The predation experiments were conducted daily for 127 days from the start, and predation was recorded every few days with a video camera; 32 videos of the Prey 1 group and 29 videos of the Prey 2 group were obtained. To detect the position of each scale-eating fish and prey fish in the tank, we fine-tuned the pre-trained neural network YOLO v3 on our dataset taken from the predation experiment. To assess the morphological features of the mouth of *P. microlepis*, we performed a geometric morphometric analysis on the lower jawbone...,