Meeting Abstract

41.5  Sunday, Jan. 5 11:15  Convergent evolution of high-performance swimming morphology in an Arizona freshwater fish MORAN, C J*; GIBB, A C; Northern Arizona University cmoran.mlml@gmail.com

Waterways in the lower Colorado River basin were historically defined by periodic flooding events as a result of snow-melt and seasonal rains. We examined the vertebral column morphology, red muscle location, and shape of the fins of roundtail chub (Gila robusta) and bonytail chub (Gila elegans), two species native to the Colorado River Basin, to test the hypothesis that native fish have evolved a morphology that enhances swimming performance. We compared the roundtail chub and bonytail chub to an invasive, low-performance swimmer from the same family, the common carp (Cyprinus carpio) and a high-performance swimmer from the marine environment, the chub mackerel (Scomber japonicus). Skeletons were cleaned and the vertebral column morphology was made visible by a colony of dermestid beetles. From intact fish, seven sections were cut along the axial body based on a percentage of standard length and the following parameters were measured: red muscle surface area and the ratio of red to white muscle for each section. Fin aspect ratio was measured as fin span squared divided by the surface area of the caudal fin using ImageJ. Native fish were not similar to mackerel in finess ratio or the red to white muscle ratio. However, caudal fin shape and the angle of the neural and hemal spines in the caudal peduncle in the bonytail and mackerel suggest that the bonytail caudal fin is modified to enhance swimming performance. A narrow caudal peduncle with folded over neural and hemal spines likely allows for hydrodynamic advantages during rapid swimming. The narrow caudal peduncle allows for minimal drag which causes the caudal fin to displace most of the water during swimming. This allows the caudal fin to do most of the work during propulsion while limiting drag forces caused by the body.