Integrative Functions of Swimming: Locomotor Mechanics in High Performance Fishes

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

This investigation will explore natural design for high performance locomotion in marine fishes. The principle goal of this work is to determine how specialized muscle anatomy in tunas (Family Scombridae) and lamnid sharks (Family Lamnidae) enhances their swimming performance. Ongoing studies of tunas have led to the hypothesis that, compared to other bony fish, the uniquely internal and more anterior location of the red muscle used for sustained swimming provides an advantage for locomotion, not a mechanical disadvantage as previously thought. Tunas and lamnid sharks, although separated for four hundred million years in their evolution, have many similarities in body form. Thus, it is further hypothesized that functional similarities in muscle contractile properties occur also, and that compared to other sharks the lamnids are indeed high performance swimmers. A comparative study of the mechanical design for locomotion will be undertaken using the short-fin mako shark (Isurus oxyrinchus). Live makos approximately 1 m in length will be collected locally, and placed in a large circular holding tank with flow-through sea water. For biomechanical studies, individual sharks will be transferred to a large water tunnel treadmill, built at the Scripps Institution, which allows fish to swim steadily against a current at controlled speeds while remaining in a fixed location relative to observers. State-of-the-art techniques will be employed to study muscle performance during swimming. Fish will be instrumented with fine wire electrodes to record muscle activation patterns. In addition, 2mm diameter sonomicrometer crystals will be implanted into red and white muscle to obtain measurements of local muscle shortening at different longitudinal positions. This digital sonomicrometry system will permit measurement of muscle deformation in three dimensions, and quantification of differential shortening and shearing between adjacent red and white fibers, which is hypothesized to occur. Coupled with these measurements will be kinematic analysis of digital video images to quantify the properties of the wave of bending that travels along the body of the shark with each cycle of muscle contraction. The resulting data set will allow a direct comparison of swimming kinematics with tunas as well as non-lamnid sharks. Also it will provide the details of muscle shortening and activation timing that are needed for in vitro muscle contraction experiments. Mechanical analysis of swimming muscle performance will focus on power production under simulated in vivo operating conditions. This will be done using the work-loop technique, in which isolated samples of muscle fibers are forced to contract cyclically as length, frequency and activation patterns are varied, and power production is measured. The novelty of this research is evident, since there are no detailed studies of muscle function in swimming of any lamnid shark. The new data will contribute substantially to the meager body of knowledge on such animals. The existing facilities, expertise, and the local availability of experimental animals together present a unique opportunity to study the locomotor biomechanics of one of the most intriguing but poorly understood marine oceanic predators.