purpel tang

I recently bought a purple tang and when I looked closely at it I noticed some white small strands on him by his tail. Does anyone know what this may be?

Selling 3 Tangs I’ve had for a few years. The Purple Tang I’ve had for 2, Sailfin for 4 and the Blue I believe for 7 when he was smaller than my Blue Chromis. They are in excellent health with no lateral line marks but I’d like to downsize to just one tang(CB Yellow Tang). Sailfin is the biggest...

:eek::eek::eek: why