Meeting Abstract

P3.127  Monday, Jan. 6 15:30  Body density of batoids in relation to ecology: Morphological control of buoyancy FISH, F.E.*; FONTANELLA, J.E.; GABLER, M.K.; SAADAT, M.; West Chester University; West Chester University; West Chester University; University of Virginia ffish@wcupa.edu

Control of buoyancy is a major factor in the ecology of aquatic animals. Buoyancy is determined by the density of an organism relative to the density of the medium in which it is immersed. Fish that occupy benthic habitats should have body densities large enough for them to sink and remain in contact with the bottom, whereas, pelagic species should maintain a relatively lower density. The body densities were determined from four genera of batoid fishes (Dasyatis, Gymnura, Potamotrygon, Rhinoptera) that were from freshwater and marine habitats and were either benthic or pelagic. Body density was measured from the weight of the rays when suspended underwater and from water displacement. All rays were denser than their respective aquatic media. Marine benthic rays had body densities that were higher than the marine pelagic ray (Rhinoptera). The freshwater rays (Potamotrygon) had the lowest densities of the rays measured. When the density of the water medium was taken into account, the density differential was lowest for the marine pelagic ray. A low relative density would be advantageous for a pelagic ray to reduce costs associated with maintaining a given depth, although the ray is still denser than medium. Computational fluid dynamic analysis indicated that the small density difference can be passively compensated for by the hydrodynamic shape of the body. The pelagic marine ray has a body profile that provides increased lift and hydrodynamic efficiency compared to benthic species.