Bleeding tail fin

Question
Hi, I'm emailing about my white goldfish. She has a nasty looking red mark on her tail fin. There has been a small red dot there for a while, but she seemed in no pain and it was almost unnoticable so I didn't worry. However, how it looks like it's bleeding inside her tail, and there's no blood in the water. Her tankmate has been going through a jumpy stage, so I'd suspect him of giving her a nip, but when I look closer it looks more like a lump inside the fin than a cut because it bulges out quite a lot. Could it be a parasite? If so, what kind and how can I treat it? Is her tankmate safe, he has no signs of lumps so far.

Answer
Hello Netty,

I'm doing some mad research for you, as goldfish aren't exactly my forte.  But what I've come up with so far doesn't seem to bad.

Since your fish seems to be ok, other than the spot, I'm wondering if perhaps filtration and water condition aren't up to par.  Have you noticed any other symptoms?  Perhaps the other goldfish's jumpiness is another symptom.

I'd start with a 50% water change today, and start thereafter with 25% water changes daily.  Fresh water added should be aged at least 24h(covered lightly to prevent contamination), and should have dechlor added, to prevent further damage from your fish.

It wouldn't be a parasite, but it may be a bacteria.  You can get a broad spectrum anti-bacterial treatment at most pet supply stores, if the one you go to does not have one, ask if they can recommend a pet store that does.  Don't wait for them to restock, however, as that can take weeks, and may harm your fish.

I'd start adding salt to the tank, a ratio of one level tsp per 1g of water.  Melafix may also be used, but I'd be sure to check that the anti-bacterial treatment you're using won't conflict.  

To sum it all up... I think your fish is either suffering from poor water conditions or from a bacterial infection.  It could have started with a nip from your other fish, and progressed from there, but I think that's unlikely, as the fish would have tattered fins and scale damage if it was being attacked.

Please don't take offense when I accuse you of poor water condition, as it can happen to all of us.  Goldfish are marketed as being suitable for small bowls, when they really need large tanks.  They get very big and are very messy.