anglefish

sounds like constapation, try giving it something that will go through its system quick like blood worms, and if that doesnt work try some live food (live brine ship work well)
What have you been feeding it? Water paramiters?

Blood worms if eaten in excess can cause constipation, try feeding some skinned peas

If your angel won't go for the skinned peas, try something like the Omega One veggie flakes which aren't just veggies, but a combination of veggies and meat. Of course, all fish are different. My angels love the spirulina pellets so go figure. I have heard daphnia also helps keep their digestive systems cleaned out. You can buy the daphnia at most of your lfs in a can under the Hikari label.