Steve Pratchett

This year in the winter on two dives I came across this juvenile Yellow Island Grouper(also known as a Comb Grouper) on the Madeira Divepoint House Reef. This one was yellow which is a rare sight. This colouration can be caused by a genetic mutation called xanthochromim where the dark chromatophores disappear unmasking yellow and orange pigments. This rare condition results in a bright yellow-to-orange fish.

Island Groupers can also rapidly reverse their colour patterns as a stress response when threatened or harassed. When this happens, the melanin in dark pigments can fade revealing brighter yellowish hues. This is not likely to be the cause in this fish 

Breeding males which become dominant and territorial can also undergo a striking transformation into a yellow-black pattern where their bodies turn bright yellow and their heads become black to attract females. As this fish is a juvenile this is unlikely got be the reason for its yellow colouration.