Stingrays

A diagnostic characteristic of stingrays in the Family Dasyatidae is the presence of a defensive, partially-serrated spine located on the tail. The objective of this study is to assess the impacts of caudal spine morphology on puncture and withdrawal performance from two stingrays, Hypanus sabinus and Hypanus say. Spines have highly variable morphology. I used an Instron E1000 materials tester to quantify the puncture and withdraw forces from porcine skin, a model for human skin. I found no significant differences between puncture and withdraw or between the species. By incorporating micro-CT scanning to quantify mineralization density, I quantified more mineralization along the shaft of the spine. Equal puncture and withdraw forces and increased mineralization along the spine shaft may create a stiffer structure that can be a persistent predator deterrent.

This study determined the electrosensitivity of a euryhaline elasmobranch,
the Atlantic stingray, Dasyatis sabina, throughout the range of salinities that it
would naturally encounter. It quantified the behavioral response of the stingrays to prey-simulating electric stimuli in freshwater, brackish, and full strength
seawater. The electroreceptive capability of stingrays from a permanent
freshwater population in the St. Johns River system was also compared with
stingrays that inhabit the tidally-dynamic Indian River Lagoon in east Florida.
This study demonstrated that D. sabina can detect prey-simulating electric fields
in freshwater, but the function of its electrosensory system is significantly
reduced. The SJR stingrays did not demonstrate an enhanced electrosensitivity
in freshwater, nor did they have reduced sensitivity when introduced to higher
salinities. The reduction in electrosensitivity and detection range in freshwater is
attributed to both an environmental factor (electrical resistivity of the water) and
the physiological limitations of the ampullary canals.

Elasmobranch fishes use electroreception to detect electric fields in the environment, particularly minute bioelectric fields produced by potential prey. A single elasmobranch family (Potamotrygonidae) is composed of obligate freshwater stingrays endemic to the Amazon River. A freshwater existence has imposed morphological adaptions on their electrosensory system due to life in a high impedance medium. Because their electrosensory morphology differs from their marine relatives, freshwater stingrays may demonstrate corresponding differences in behavioral sensitivity. The objective of this study was to quantify behavioral sensitivity of the obligate freshwater stingray Potamotrygon motoro to prey-simulating voltage. The voltage produced by common teleost prey of P. motoro were measured and replicated for behavioral trials. The best response was 10.62 cm, and the smallest voltage gradient detected was 0.005 mVcm-1. This sensitivity is reduced compared to marine species. The conductivity of the medium, more so than ampullary morphology, may dictate sensitivity of the elasmobranch electrosensory system.