Hydrodynamic Imaging by Blind Mexican Cavefish

Abstract

Blind Mexican cavefish (Astyanax mexicanus) live in complete darkness in underground streams and pools. These eyeless fish use hydrodynamic imaging to sense their surroundings. Hydrodynamic imaging involves fish using their mechanosensory lateral line system to sense changes in the water flows around their body caused by the presence of nearby objects. This allows them to sense detailed information about their surroundings as they move through complex environments. The fluid dynamics associated with this remarkable ability have been revealed using experimental flow measurements and computational modelling. Measurements of the fish’s behavior and of the flow fields around the fish show that hydrodynamic imaging has a short range, of the order of 10 % of the fish’s body length, and that fish need fast reactions in order to use it for collision avoidance. Due to the fluid dynamics of the flow fields involved, this sensory range is not increased when fish swim faster, contrary to previous expectations. This chapter summarises the behaviors and fluid dynamics involved with hydrodynamic imaging as used by blind cavefish.