When Designing Rays, Function Matters

Meeting Abstract

P2.48  Friday, Jan. 4  When Designing Rays, Function Matters CHADWELL, B.A.*; HUNTER, B.W.; ASHLEY-ROSS, M.A.; Wake Forest Univ; Wake Forest Univ; Wake Forest Univ chadba1@wfu.edu

Ray-finned fishes can actively control the shape and orientation of their fins. Due to the segmented, bilaminar design and actuation by multiple pairs of fin muscles, fish can control the rigidity and curvature of individual fin rays independently. This unique ability allows the fish to vary the resultant forces across its fin surfaces. Recent studies have demonstrated that bluegill sunfish alter median fin kinematics depending on which locomotor behavior is performed. While fin anatomy for several taxa have been characterized, few studies describe the variations among individual fin rays. Expecting that differences in mechanical properties should be reflected in their structure, we measured several skeletal and muscular features of individual spines and rays of the dorsal and anal fins of bluegill sunfish, comparing not only the differences between fins, but also among rays/spines within fins. Movements of spines are constrained primarily to the sagittal plane (elevation & depression), with the erector muscles predominating. Rays are able to move in the sagittal and transverse planes, with inclinator, erector and depressor muscles (mI, mE & mD) of similar sizes. For all muscle pairs, muscle mass varied with longitudinal position of the spine/ray. For mI & mD, mass was greatest at or near the middle ray for both DF & AF, with muscle mass decreasing in both directions. However, peak mE mass occurred at the 3rd or 4th spine. Among rays, the percentage of ray length that was segmented and branched was increased with a more posterior position. The variation among the spines and rays corresponds well with the variety of kinematic patterns observed. In particular, the wide range of motion and evenly distributed muscle mass among rays makes possible the use of fins as control surfaces under a variety of locomotor repertoires.

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