The Relation Between Structure and Bending Properties of Teleost Fin Rays

In the segmented, soft fin rays of the tailfin and pectoral fins of the teleost fish Sarotherodon niloticus (L.) (syn. Tilapia nilotica L.) transverse collagenous fibers with a serpentine, curly appearance connect the hemitrichia. Experimentally applied shift of the hemitrichia of isolated tailfin rays relative to one another causes bending of the ray. The role of the transverse fibers is discussed. The serpentines have elastic properties ; when shift is applied at the hemitrichium bases, the ray bends over its entire length. The degree of curvature at any position along the ray is proportional to the applied shift, but reaches a maximum level when the transverse fibers attain a state of maximum extension.