LANDELS, C.; GIBB, A.C.; Northern Arizona University; Northern Arizona University: Kinematics of the aquatic escape response in Periophthalmus argentilineatus: Do mudskippers “skip” underwater?

Periophthalmus argentilineatus, also known as the mudskipper, is an amphibious fish species. Because members of this species are amphibious, they produce both aquatic escape responses (“C-starts”) and terrestrial ones (“skipping”) when fleeing predators. Both responses begin with extreme lateral bending, and thus appear to be superficially similar. We recorded aquatic escape responses at 500 frames per second using a Redlake PCI 1000S high-speed, digital-video system and analyzed images using a custom digitizing program. Several sequences for each of six mudskippers were used to calculate timing and bending variables, including the curve coefficient (the ratio of the distance between the two ends of the vertebral column when the fish is maximally bent versus straight). These variables were compared with similar variables measured from previously collected terrestrial escape responses for the same individuals. We found that relative to terrestrial responses, aquatic responses were slower and produced less bending. For instance, it took the mudskippers twice as long to achieve maximum curvature in water. In addition, maximum curvature, as measured by the curve coefficient, was greater on land than in water. In summary, although there were similarities between aquatic and terrestrial escape responses, they were quantitatively different. These differences may be due to the higher viscosity of water; alternately, the nervous system may trigger a different behavior in each of the two habitats.