Goldfish is sick

My sister's goldfish is ill. The fish is swollen and is upside down all the
time, swimming on its back.

Can anyone tell me what might be wrong with the fish and what can be done
for it?

Thank you.

Have you tested your water parameters (ammonia, nitrite , nitrate, PH)? Bad
water quality is often a cause of fish illness.
It does sound like there could be a swim bladder problem though, so as well
as testing your water, starve the fish for 3 days, then feed nothing but
defrosted, shelled and chopped frozen peas for another 3 days. Then slowly
reintroduce normal food but always soak this in a little tank water for a
few minutes before feeding to aid digestion and stop air getting trapped.
Mel.

"Janice" <Janice RemoveThis @anon.co.uk> wrote in message
news:5%%gb.8466$RU4.81943@newsfep4-glfd.server.ntli.net...
> My sister's goldfish is ill. The fish is swollen and is upside down all
the
> time, swimming on its back.
>
> Can anyone tell me what might be wrong with the fish and what can be done
> for it?
>
> Thank you.
>
>