Albinism is characterized by an absence of pigmentation in the skin, hair and eyes. It is a congenital disorder and is caused by a disruption of the enzymic pathway responsible for producing melanin. Albinism has been widely reported for many invertebrates and vertebrates and is very commonly documented in bony fishes.
There are, however, only a few records for sharks and rays, and most of them were partial albinism, where skin pigmentation is lacking or reduced but retinal colouration is normal. Overall, albinism in sharks is rare and no case of full albinism has ever been described for a skate species.
|Taken from Ball et al. 2013|
Now a paper published in the Journal of Fish Biology reports three cases of albinism in recent years (2008, 2011), which compares to only four documented accounts of partial albinism in rays since 1893. The three albino skates were captured from the North Sea and the English Channel. A high level of morphological conservatism among skates and rays usually makes them challenging to identify even when the regular coloration is present. By using DNA Barcoding and morphometric analyses, the researchers were able to identify the albino individuals as a spotted ray Raja montagui, a blonde ray Raja brachyura and a thornback ray Raja clavata.
It remains unclear whether this find represents a genuine increase in albinism with some biological significance. Widely reported declines in U.K. skate populations have given rise to concern over their conservation status and an increased focus on their fisheries management. The albino findings may be purely coincident with a general increase in fishing intensity and reporting requirements. Rajids were not subject to mandatory species specific landing according to European law until 2008, hence, before this time, any unusual morphology may have been overlooked.