Help with goldfish disease (photos)

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My husband has bought a new goldfish for our tank but didn't notice its anal fin is almost missing and the area looks diseased. The fish otherwise seems to be swimming around happily, eating fine and all other fins are perfect. Can anyone advise what this is and what treatment I'd need? I have looked on Google but struggling to know whether it's an ulcer, flukes or something else entirely. Thank you

Parameters were spot on a couple of days back. I did a 25% water change on Wed morning, expecting the Melafix to arrive that day. He is spending a lot of time sitting on the gravel now. His dorsal fin is still up though and he comes straight to the surface for food when the filter is switched off.

That's interesting about the colour changes! We won't keep him though. Just hoping to nurse him back to health then move him to a pond in the spring.

Hmmmm. Aside from the most common cause which is water issues, which you can't really do anything about while using melafix as water changes will mess up the dosage, it could be stress from the move, how have the other fish adjusted to him? What type of fish are they?

Other than that my mind goes to swim bladder issues or possibly parasites. But I'm more inclined to think water/stress.

You're doing your absolute best by him, if you do run out of options there is a goldfish rescue, they have a Facebook group that is good, maybe they could find somewhere for him? It's called the fish welfare and rescue.

Sorry! It's Fish Rescue and Welfare.

www.facebook.com/share/WMXSjyGjod9SGQms/?mibextid=K35XfP

I'm confident on the water quality. I will add the aquarium salt when that arrives. There are two other fish in the tank which we've had for quite a few years. One is a redcap, the other looks like a shubunkin in colours but has a fantail. Both these old fish are looking and acting completely normally so nothing has obviously spread (so far). All the fish get along fine. I haven't seen any bullying whatsoever.

you dont need aquarium salt you can use rock salt from asda, it ill help perk her up, what foods are you feeding? floating or sinking pellets? do they have greens in them such as spirulina, you can also add garlic to their food some will take it in chunks others use drops on their food this will help build up a good immune system.

Thanks - I've already ordered aquarium salt but will bear that in mind for next time. I just feed Aquarian coldwater flake food. Sometimes I shell and chop peas as well. I've never given garlic - that's amazing!

I've just added the third dose of Melafix. The fish looks less happy now and is intermittently clamping his fins. The wound looks worse, like it's eating more into the body. Must be so sore 😔

yeah all you can do at this stage is keep up with the treatment, forgot to ask do you have catfish in there before you add salt?

No catfish. Will definitely keep on with the Melafix and hope for the best.

try also feeding sinking pellets especially as you say you have a fantail, goldfish can gulp air at the surface which can give them bloat which can then lead onto swim bladder issues, do you by any chance have a heater lying around as warming the tank up can speed up metabolism which can speed up recovery only do this for maximum 2 weeks though as it can speed up growth, but only body growth, sometimes then internally they can struggle to keep up

I don't have a heater unfortunately. I've never kept tropical fish