Eye convergence is evoked during larval prey capture (LPC) without visual stimulus and in blind cavefish

In zebrafish larvae, the first response when detecting prey is an oculomotor behavior; eye convergence. Eye convergence increases the overlap between the visual fields of the left and right eyes to prepare for tracking prey. A high vergence angle is maintained throughout the prey-tracking and capture swim phases, enhancing binocular depth. Since the discovery of eye convergence, hundreds of articles reporting on this behavior in zebrafish have been published. In this study, we found that the larvae of blind tetra cavefish, Astyanax mexicanus, despite being adapted to the absence of visual stimuli due to the lack of light in the cave, have retained the oculomotor behavior of eye convergence in their vestigial eyes. In Astyanax, eye convergence responses can be triggered singlehandedly by vibrations elicited with a glass rod at frequencies similar to those generated by its prey (10-35 Hz). The blind cave tetra offers an intriguing combination of regression of the eye structure, while retaining several of the physiological functions and actions performed in the eye, including light-entrained retinomotor rhythms and eye convergence.