Hello.

About four days ago I purchased a new Red & White Comet at a local pet store. He seemed happy and healthy when I bought him. Now, he is pretty lathargic. His fins are closed tighty against his body, and he is not very active at all. He is eating, and occasionally opens his fins and swims around a bit. He is living with a few other Goldfish (Comets). The other fish are very active and seem very healthy.

What might the problem be?
Any suggestions I can try to ail my fish, if he is infact ill?

Thanks.

Yes, he sounds very ill. It's hard to say what's the cause without more information and symptoms. Clamped fins may indicate parasites or bacterial problems. Your other fish have probably been exposed but you might separate them ASAP in case they haven't. In the future, quarantining is a good idea. Your fish might have something easy to cure like ick or something worse like an internal bacterial infection.

I used to raise goldfish a long time ago and had plenty of problems with them getting sick. Sounds like a bacterial infection, but I can't be sure. Like Robyn said, the best thing to do is to quaratine that comet and possibly treat it.

I've never had luck with treating the entire tank, so I don't suggest you do that unless they all show the same symptoms down the line. Make sure you do 20% water changes in the main tank twice a week for a while and that nothing stresses out your other fish.

I've read good things about Melafix and the Maracyn antibiotics as treatments.

Today, my Comet seems to be more active. He is swimming around with his fins open and pecking at the live plants with the rest of the Comets. I have noticed there are a few small black spots on his skin and the tips of his fins. They don't look like parasites to me, but I am far from an expert. There are a couple small spots on one gill, and some spots on the tips of his rear fin. It looks more like he is changing color. I have read that some goldfish can turn black, but can a red and white Comet do this too?

I have some MelaFix on hand. I had to use it for my Platies, but that's another story. I think I will quarintine the Comet in question, and give him some MelaFix and a small dose of aquarium salt.

I am learning the hard way that I should quarantine all new fish. Before, I would normally only quarantine my feeder fish; and its a good thing to, I just lost eight new Rosey Red Minnows to something. I'm sure glad I didn't feed them to my turtles.

I'm glad your comment is doing better. How big are the black spots. If they aren't much larger than a pin head, then he may have black spot parasites which can be treated with anti-parasitic medications. If instead, the black areas are blotches, they could be color changes but since your comet is already red and white I would highly doubt reversion to black coloration. Injured areas of the fins will also turn black while they're healing.