I have a 2 year old chalk bass with a sunken belly. It always gets his fair share of food compared to other tankmates, I don't know what the problem is. None of the other inhabitants have it. I googled generic images of the fish to see if it is just how it normally looks, but many chalk bass out there have plump bellies. The last one I had 2 years prior had the same issue and died of unknown causes. Any advice?