kevy said:
something sticking out. About half a cm sticking out, and another half that is visable under the skin. It looks like of like a splinter but I'm thinking some kind of large parasite?
kevy-
I was hoping someone with more experience could help you with this since I'd hate to make a guess and give you the wrong answer. But, since no one else has, I tried to look it up in a good tropical fish reference book that I have.
Most of the parasites they list are usually found on cold water fish like goldfish and koi that are raised in ponds. Often they will die in a warm water tank.
Do you think you could net the fish and just take it off with tweasers? Or you might try a salt bath. I am suggesting these as possible first aid measures. If there is only one parasite on the fish, this will solve the problem.
On the other hand, if it was raised in an environment where it could get that parasite, it might have other types as well. Some parasites live in the gills or under the scales and are not visable.
I strongly suggest that you look for a good independant fish shop---not a chain store. Here you will find someone who is experienced and knowledgable with the problem and who could suggest a cure. You may be able to describe the problem and get help or you may want to bring a picture of the fish or the fish itself to show him. You will have to go to a lfs to buy medecine anyway so I really do think this is the way to go with this matter. There is not much point in guessing and since the medecine is poison you want to be sure to get the right one the first time.
In any case, good luck and please let us know what it turns out to be and what you have done to cure it.