Diverse prey capture strategies in teleost larvae

Animal behavior is adapted to the sensory environment in which it evolved, while also being constrained by physical limits, evolutionary history, and developmental trajectories. The hunting behavior of larval zebrafish (Danio rerio), a cyprinid native to streams in Eastern India, has been well characterized. However, it is unknown if the complement and sequence of movements employed during prey capture by zebrafish is universal across freshwater teleosts. Here, we explore the syntax of prey capture behavior in larval fish belonging to the clade Percomorpha, whose last common ancestor with cyprinids lived ~240 mya. We compared the behavior of four cichlid species from Lake Tanganyika endemic to deep benthic parts of the lake (Lepidiolamprologus attenuatus, Lamprologus ocellatus, and Neolamprologus multifasciatus) or inhabiting rivers (Astatotilapia burtoni) with that of medaka (Oryzias latipes), a fish found in rice paddies in East Asia. Using high-speed videography and neural networks, we tracked eye movements and extracted swim kinematics during hunting from larvae of these five species. Notably, we found that the repertoire of hunting movements of cichlids is broader than that of zebrafish, but shares basic features, such as eye convergence, positioning of prey centrally in the binocular visual field, and discrete prey capture bouts, including two kinds of capture strikes. In contrast, medaka swim continuously, track the prey monocularly without eye convergence, and position prey laterally before capturing them with a side swing. This configuration of kinematic motifs suggests that medaka may judge distance to prey predominantly by motion parallax, while cichlids and zebrafish may mainly use binocular visual cues. Together, our study documents the diversification of locomotor and oculomotor adaptations among hunting teleost larvae.