HSIEH, S.T.; Harvard University: Fish out of water: the amphibious locomotor repertoire of the Pacific leaping blenny, Alticus arnoldorum

The evolutionary transition from water to land required dramatic alterations to organismal morphology, physiology, and ecology. Among extant fishes, the ability to come out of water has evolved multiple times. One of the most spectacular examples of amphibious lifestyles in fishes is exhibited by the Pacific leaping blenny, Alticus arnoldorum. Described as being almost hydrophobic, these fish are found in large numbers on rocks along the coastlines of Guam, and exhibit an extraordinary repertoire of behaviors that permit extremely rapid locomotion on land. They can leap up to five body lengths between rocks, appear to ‘skip’ on the water surface, and can climb smooth, vertical surfaces. They are often found clinging to the undersides of algae-covered rocks. I hypothesize that these novel, acrobatic behaviors are derived from movements commonly employed by fully aquatic fishes. I filmed A. arnoldorum with two high-speed video cameras (250 fps, 1/1250 s shutter) as the fish moved freely in a glass tank. The cameras were oriented such that one filmed the dorsal, and the other the lateral view. Motions of these fish were then digitized and transformed into three-dimensions using direct linear transformation. Preliminary results indicate that during ‘aerial’ locomotion, these blennies utilize the same C- and S-start behavior as fully aquatic fishes. They use S-starts primarily to exit water; for example when leaping out of water to stick on a vertical rock face, or to continue a ‘skip.’ They use C-starts as an escape response on land and for jumping from a solid surface. Their regular locomotion across rocks resembles a modified C-start.