One of my male guppys has a swollen belly. I'm not sure if it is just because it is a pig, or if it is sick. it is acting normal and nothing else looks strange about it but he does not hang out with the others as much. Ihave been watching it for over a week and it does not look to be getting smaller. I think something is wrong. Should I dose Pimafix? how can I be certain this will help?