This is a discussion on growth under gill flap within the Tropical Fish Diseases forums, part of the Freshwater Fish and Aquariums category; -->
my fish has this strange white growth protruding from under neath his gill flap....any ideas what it could be? It looks like a hard-mass... ...
That could be any of a number of things. Its difficult to say based on these photos. Is the fish having any problems with breathing, eating, or swimming?
How long has this been there? Has it changed in size or shape since you first noticed it? Can you please provide tank stats such as water params, temp, foods you're offering, feeding schedule, etc? The more info you list the easier it will be to diagnose the problem and treat it safely.