Concave Belly On Juvenile Male Platy

[Mamashack]

I have just noticed that one of my juvenile male platies has a funny-shaped belly.
Instead of making a convex shape his belly looks concave as tho he is holding it in and his bottom line is parallel to his top line.
It does not appear to cause any any problems other than I have noticed he tends to go for crushed flake rather than pellets which I feed a mixture of each day.
It's not a particularly good picture, but I think it shows what I'm trying to describe.
Can anyone shed any light on what might be happening?
 

 

[betta fish]

Internal Parasites perhaps? that's the first thing that springs to mind.

 

[Mamashack]

Oh I do hope not!
How would I know if that's that case?
I think I'd better go and do some research!

 

[DerpPH]

Oh I do hope not!
How would I know if that's that case?
I think I'd better go and do some research!

White stringy poo and general weakness or slowness

 

[star4]

If he has stringy white faeces then you need an anti internal parasitic medication like sterazin. If you see stringy red worms hanging from his anus you would need sera nematol which treats camallanus worms.

 

[Mamashack]

Thanks star4 & Derp - he has as much energy as ever and no white stringy faeces or red worms from his anus. He's still eating altho he can't manage the pellets but he's not afraid to challenge others for the crushed flake.

 

[Mamashack]

Must have caught his condition just as it was starting. I had to cull him this morning as he became more and more emaciated over the last couple of days so clearly wasn't getting as much food as I thought. My understanding is that parasites don't kill their host or they'd lose their food source. If it was parasites where did they come from? They haven't been fed live foods in fact nothing different to what they've been getting for the past couple of years.
 
Is there anything I can do for the other fish in the tank? They look ok at the moment, no poo visible let alone stringy poo, and no red worms, normal shape, swimming and eating healthily. Should I leave well alone?

Just remembered I did put some ramshorn snails in there a month or so ago for the assassin snails and as far as I can tell they've all gone now. Could they have brought parasites with them?