Sturgeons, sharks, and rays have multifocal crystalline lenses and similar lens suspension apparatuses

Blurry eyes and clouded minds: Metal and metalloid contamination of the visual-sensory system of elasmobranchs

Marine metal and metalloid pollution poses significant risks to elasmobranchs, especially in vital organs such as their sensory and visual systems. While contamination studies have traditionally focused on elasmobranch liver and muscle tissues, due to their significance in detoxification processes and human consumption, respectively, the eyes and brain of this group remain largely underexplored in ecotoxicology assessments. Metal and metalloid accumulation in these sensory organs may compromise key elasmobranch functions, impacting crucial survival behaviors, such as foraging and predator evasion. Detecting sublethal cellular effects caused by these contaminants in the eyes and brain employing biomarkers offers a pathway to assess pollutant sensory health effects before they extend to the organismal and population levels, although no studies have been carried out to date in this sense. This review compiles the current knowledge on metal and metalloid contamination in elasmobranch sensory systems, highlighting the need for further research to understand pollutant effects in these animals' ecological roles and inform conservation strategies.

Visual discrimination and resolution in freshwater stingrays (Potamotrygon motoro)

Potamotrygon motoro has been shown to use vision to orient in a laboratory setting and has been successfully trained in cognitive behavioral studies using visual stimuli. This study explores P. motoro's visual discrimination abilities in the context of two-alternative forced-choice experiments, with a focus on shape and contrast, stimulus orientation, and visual resolution. Results support that stingrays are able to discriminate stimulus-presence and -absence, overall stimulus contrasts, two forms, horizontal from vertical stimulus orientations, and different colors that also vary in brightness. Stingrays tested in visual resolution experiments demonstrated a range of visual acuities from < 0.13 to 0.23 cpd under the given experimental conditions. Additionally, this report includes the first evidence for memory retention in this species.