Effects of Temperature and Anesthesia on Visual Temporal Resolution in Elasmobranch Fishes

An organism’s ability to track moving objects, or temporal resolution, has been correlated to habitat and lifestyle, and can be further modulated by temperature and light intensity fluctuations within the environment. Photopic (bright-light/day time) vision is typically faster than scotopic (dim-light/night time) because visual sensitivity is greater in dim light and integration time must be slowed to allow for capture of the maximum number of photons. Higher temperatures result in increased temporal resolution in both endothermic and non-endothermic fishes. Previous studies have used either anesthetized or paralyzed fishes to determine temporal resolution, measured as the maximum critical flicker fusion frequency (CFFmax). However, sedation with the anesthetic, tricaine methanesulfonate (MS-222), is thought to suppress sensory system responses, although empirical evidence is lacking. Therefore, we quantified scotopic and photopic CFF _max in the yellow stingray, Urobatis jamaicensis , at the extremes of its temperature range, 20°C and 30°C, and immobilized with anesthesia, MS-222, or a paralytic, Pavulon. Both low temperature and anesthesia (MS-222) reduced CFF _max . With an increase of 10°C, CFF _max doubled from 12Hz to 25.3Hz (photopic) under Pavulon, whereas CFF _max increased by only 4Hz, from 6.7Hz to 10.7Hz (photopic) under MS-222 anesthesia. In general, MS-222 anesthesia minimized the effects of both temperature and light-adaptation compared to Pavulon. Yellow stingray CFF _max was similar to the skate, another benthic batoid, but slower than shark species studied with the same technique. These results illustrate the effects of light adaptation, temperature, and anesthesia on visual function within the elasmobranch fishes.