Re: Cory catfish red mark
#2
To me, that looks like a simple superficial marking/feature pertaining to that particular fish, rather than anything to be alarmed about. If the insides of the gills were inflamed/blood-red in colour, and he was behaving differently or not eating, that would be a different matter entirely. If the situation changes in any way, let us know and we'll advise further. How long have you had him and the rest of the shoal?