Hello,
You can try feeding some frozen green peas without the shells. yo see if this will relieve the constipation. This also may be a parasitic issue or swim bladder. Try the Peas first and see if this will relieve the problem. If not you may have to look into some medication for swim bladder. Joan
From your description if it is constipation that is what is used for fish to help them to move stool. We use this in most fish. You may also want to add a couple of grains of Epsom salts to the peas this will also help with constipation. I would also do a water check to be sure of the nitrite levels and ammonia. If you find the levels are off try to do a 25% water change. You can also add a bit of aquarium salt to the water to help with the problem. I have included a link below of a similar problem like what you are having and how it was treated. Joan
http://en.allexperts.com/q/Freshwater-Aquarium-3216/Oscar-slowly-dying-4.htm
Vet. Tech.
I am a Vet Tech for over 30 + years and have four rescued dogs of my own