Hi, My mum has a 3 foot tank and only 5 fish remaining. 1 x 10cm bristlenosed cat, 2 neon tetras, 1 black tetra and another kind of tetra which i think is female. The only thing is this last tetra we have only noticed has a huge belly. You would think it was pregnant but i cannot see gravid spots and it's spine looks a little distorted. I have pregnant guppies and they look completely different. It goes to the bottom of the tank and stays there a while so we thought it could be about to give birth but that was a week ago. Now we are worried it could have a disease, be in pain or be constipated. It has been in the tank with no new fish for years so we find it funny it suddenly is pregnant. Any ideas on what it could be? I will try to post a picture but it looks like a tetra with a humumgous belly.