LAURITZEN, D.V.; GORDON, M.S.*; WIKTOROWICZ, A.M.; Univ. of California, Los Angeles; Univ. of California, Los Angeles; Univ. of California, Los Angeles: Swimming biomechanics and kinematics in aracanin boxfishes

The temperate water Australian boxfishes (family Ostraciidae, subfamily Aracaninae) differ morphologically from the widely distributed and more familiar tropical boxfishes (subfamily Ostraciinae) in two major respects: (i) The bony carapaces covering most of their bodies end posteriorly just anterior to the insertions of the dorsal and anal fins rather than ending behind those insertions. (ii) The carapaces have only single mid-ventral keels rather than two or more variously positioned lateral keels. These differences correlate with, and probably permit, a major difference in swimming modes between the two groups. Aracanins swim using tail-wagging body and caudal fin (BCF) locomotor modes rather than the rigid-bodied, median and paired fin (MPF) modes characteristic of the ostraciins. Aracanins are also more strikingly sexually dimorphic than are ostraciins. We have studied swimming biomechanics and kinematics in both sexes of two aracanin species. As compared with four different ostraciins studied previously aracanins have significantly lower upper critical swimming speeds. Rectilinear swimming movements are substantially more dynamically stable than is usually the case for fishes using BCF modes, however significant yawing recoil movements occur. Synchronization between pectoral fin and dorsal/anal fin movements appears significantly more variable than is usual for ostraciins swimming over similar ranges of speed. Gait changes occurring as fishes swim more rapidly appear less dramatic and clear cut than is usual for ostraciins. Measures of maneuverability appear similar in the two groups. We will discuss possible ecological and evolutionary implications of these differences.