My minnow is deformed and miserable

[baddyfreckleface]

I have a 90L tank with 6 minnow, 6 danio and a snail. We have had it since last summer and so far no deaths!
I have been keeping an eye on one of the minnows as he looks very thin and always hangs out alone at the back even when they are fed. He looks so sad! (For a fish)
I'm pretty sure he is deformed as his shiny flash down his spine arches up slightly and then down. So that his tail kind of points down.
I never see him eat. Even if I feed all the eager ones away from him and slip him a bit of food right over his head while the others are distracted. He just doesn't eat it. He has no tummy at all. It's basically concave where the others have tummies. (Or whatever the fish equivalent is)

I'm not sure what to do about him. He looks sad and incredibly small and thin but then he must be eating something as he's still alive. Is he suffering?

I will try and attach a picture

ok so I haven't found myself a good aquatic shop yet then!

I don't especially want tropical or more fish at all anyway as I seemed to have a good balance until now. I am happy cleaning out once a week and like being able to leave it a bit longer if I don't get a chance because it's never desperate for a clean.

I just wanted to find a place with good advice so I could start going there for my fish stuff

Yeah, I'm the same, I don't like to have to do loads of extra water changes and testing just for the sake of a few more fish. My tank is very heavily planted so it would look nice even with no fish in it.

If there's a Maidenhead Aquatics near you, they are usually pretty good.