Meeting Abstract
Herbivorous fish feed by biting, tearing or scraping algal material off the substrate. Due to their neutral buoyancy, fish feeding off hard surfaces may experience a recoil force pushing them backwards as they bite their food. To successfully detach prey items from hard substrates, fish need to constantly generate thrust in order to maintain contact with the substrate and pull the prey away. However, studies on adaptations for herbivory in fishes have hitherto focused on the jaws and teeth, neglecting the role of thrust-generating mechanisms. We hypothesize that these fish coordinate body and fin movements with mouth kinematics to facilitate algal removal. We used an underwater video system composed of two synchronized high-speed cameras, to observe the feeding kinematics of two Zebrasoma species in situ, in the coral reef. The system provided accurate 3D kinematics of the fish’s mouth, fins and body, while a synchronized load cell recorded the forces exerted by the fish while feeding from a feeding plate. We found that bites were characterized by stereotypic and coordinated movements of the mouth, head and fins. Fish opened their mouth when approaching the feeding plate, reaching peak gape and often starting to close the mouth before initiating contact with the plate. Sideways head flicks accompanied almost all the bites. Upon mouth closing on the algae, fish swung their head laterally while moving their pectoral fins forward. This coordinated movement exerted a pulling force that was used to tear the algae from the substrate. Our results show that thrust generating mechanisms play a crucial role in the feeding success of herbivorous fish and suggest that adaptations for hard surface feeding expand beyond teeth and jaws.
