floating gold fish

Question
one of my goldfish which has been in my tank for three weeks has suddenley started to float on the top of the tank with its back out of the water. as much as it trys to it cant get down to the bottom, its slightly tipping to the side like it has no balance. its moving ok along the top and still chases food when we feed them. what could be wrong and what can we do to help it? thank you .  

Answer
Hi Dawn;

It sounds like a swim bladder problem. Here is more info;

http://www.netpets.com/fish/reference/freshref/swimbldr.html
http://www.petplace.com/fish/when-your-fish-can-t-swim/page1.aspx

I hope he feels better soon......

At Your Service;
Chris Robbins