Feeding behavior and kinematics of the lesser electric ray, Narcine brasiliensis (Elasmobranchii: Batoidea).

Jaw protrusion is a major functional motif in fish feeding and can occur during mouth opening or closing. This temporal variation impacts the role that jaw protrusion plays in prey apprehension and processing. The lesser electric ray Narcine brasiliensis is a benthic elasmobranch (Batoidea: Torpediniformes) with an extreme and unique method of prey capture. The feeding kinematics of this species were investigated using high-speed videography and pressure transduction. The ray captures its food by protruding its jaws up to 100% of head length (approximately 20% of disc width) beneath the substrate and generating negative oral pressures (< or = 31 kPa) to suck worms into its mouth. Food is further winnowed from ingested sediment by repeated, often asymmetrical protrusions of the jaws (> 70 degrees deviation from the midline) while sand is expelled from the spiracles, gills and mouth. The pronounced ram contribution of capture (jaw protrusion) brings the mouth close enough to the food to allow suction feeding. Due to the anatomical coupling of the jaws, upper jaw protrusion occurs in the expansive phase (unlike most elasmobranchs and similar to bony fishes), and also exhibits a biphasic (slow-open, fast-open) movement similar to tetrapod feeding. The morphological restrictions that permit this unique protrusion mechanism, including coupled jaws and a narrow gape, may increase suction performance, but also likely strongly constrain dietary breadth.