Meeting Abstract
The position of the fins on the body has changed significantly in the evolution of ray-finned fishes. Accompanying these changes in fin position have been changes in fin function. Salmonids like the Coho salmon (Oncorhynchis kisutch), have fin placement that is intermediate between more basal ray-finned fishes like sturgeon and more derived fishes like yellow perch. Fin function is largely determined by the relative stiffness and flexibility of the bony segmented fin rays, or lepidotrichia, that support the fins. Little is known about the morphology and stiffness of the paired fins and median fins in fishes in intermediate phylogenetic positions like salmonids. We examined the external morphology and used a three-point bending testing method to quantify stiffness in a sample of fin rays from the dorsal, anal, pectoral and pelvic fins. We used a mixed linear model approach to statistically evaluate the degree of stiffness among fins, but also within individual fin rays along their proximo-distal length. Our previous research has shown that the pelvic fin was the most stiff and pectoral the least stiff in more derived fishes like yellow perch, with median fins stiffness in between. We found the same pattern in Coho salmon. However, we found differences in stiffness of the fin rays among the fins in Coho salmon. In the paired fins, the leading and training edges were more stiff than we would predict based on their size. Alternatively, the fin rays in the median fins were stiffer in the middle versus the edges than we would predict based on size. This suggests that cross-sectional morphology may play an important role in determining the function of lepidotrichia. We also present preliminary results comparing the three-point testing method to a curvature-based testing method.
