Sharks, skates and rays may be able to see in colour much like us, according to a study published in a recent issue of the Journal of Experimental Biology.
Sarah Van-Eyk and co-authors conducted a series of behavioural experiments based on visual discrimination tasks to test if the giant Shovelnose ray (Glaucostegus typus) possesses colour vision.
Very little is known about whether or not elasmobranchs (sharks, skates and rays) are capable of colour vision. Even though the presence of colour-detecting cells in the retina was recently discovered in the giant shovelnose ray, it is still necessary to conduct behavioural experiments to find out if the ray was actually capable of discriminating colours.
The authors first trained two juvenile Shovelnose rays to eat from a feeder, with the feeder dispensing food only if they touched a sheet of laminated blue paper next to the feeder. They then removed the feeder and fed the rays only when they touched the blue paper.
Once the rays were trained, the authors then started the first series of experiments, which consisted of presenting the rays with the blue paper together with three similar-sized grey papers of varying brightness all mounted on a Perspex board.
The rays were required to touch the blue paper with their snout before they received a food reward; the trial was terminated and the rays were not given the food if they touched any of the grey papers instead of the blue one.
In the second series of experiments, the authors varied the intensity of the blue papers presented to the rays, with the conditions of the experiment being identical to the first.
In at least 75% of the time, both rays were able to correctly distinguish the blue paper from the grey ones, implying that they were capable of distinguishing colours.
For more information, see the paper: Van-Eyk, SM, UE Siebeck, CM Champ, J Marshall and NS Hart (2011) Behavioural evidence for colour vision in an elasmobranch. Journal of Experimental Biology 214, pp. 4186–4192.
Why not take out a subscription to Practical Fishkeeping magazine? See our latest subscription offer.