Morphology and kinematics of prey capture in the syngnathid fishes Hippocampus erectus and Syngnathus floridae

The mechanism of prey capture in two syngnathid fishes, the lined seahorse Hippocampus erectus (Ferry) and the dusky pipefish Syngnathus floridae (Jordan and Gilbert), is described based on anatomical observations and high-speed video recordings (200 and 400 images s(-1)) of feeding events by four seahorses and three pipefish. The fish were collected near Turkey Point, Florida, U.S.A., in January 1994 to March 1995. The dominant features of the morphology of these and many other syngnathiform fishes include extreme elongation of the suspensorium and neurocranium with a small mouth located at the anterior tip of the head. In the seahorse, a preparatory phase of prey capture consisted of slow ventral head flexion. This was followed by rapid elevation of the head and snout as the prey was drawn into the mouth by suction. Both H. erectus and S. floridae capture prey rapidly, with peak head excursions and mouth opening occurring within 5 to 7 ms of the onset of the strike. There was no upper jaw protrusion. In both species the time to recovery of the cranium and hyoid apparatus to resting positions was highly variable but took at least 500 ms. Manipulations of freshly dead specimens indicated a biomechanical linkage between head elevation and hyoid depression. However, the predictions of a previously proposed four-bar linkage model that couples hyoid depression to head elevation were not fully supported by kinematic data from one seahorse, suggesting that additional linkages act during the expansive phase of prey capture. These species exhibit the generalized kinematic pattern of prey capture in bony fishes, with head elevation, hyoid depression and mouth opening occurring almost simultaneously. The derived morphology results in a unique feeding behavior, in which prey are captured during a sudden upswing of the head, which brings the mouth to the prey. Suction is used to draw the prey into the buccal cavity.