The fish is a normal goldfish (not fantail/oranda or anything) and around 15cm long.
It is quite a big tank with 2 other adult fish, 1 medium and 4 babies. (Baby fish all bought from shops and not concieved within tank)
I change the water about every 2 or 1.5 months… and generally the water is clean and clear.
I compare it to the other adult fish (I bought them both at the same time) and the other one seems healthy and has not got a red bump on its head.
I don’t think that the fish is stressed out or anything, and it does not bully/ get bullied by other fish.
I feed them twice a day and watch to make sure each fish eats and that one fish doesn’t take all the food.
I dont think it is a bruise, or a vessel popping in it’s head.
I have tried to do some research and have been unsuccessful, just to make it clear it is NOT a fancy goldfish, just a normal goldfish living in a coldwater tank.
I think it may be common since I have seen something similiar on my other fish, (however my other fish was a fantail and I later found out the disease) I hope something can be done and it is curable!
But I do not know what it is and if it is dangerous or infectious/contagious.
Sorry for the long paragraph, I want to know if there is a cure and what should be done and what it is?
I will try and take a picture and upload it however he/she swims around a lot so it is hard.
Any information welcome! I got it for my 9th birthday (so is very special!) so he is about 5 years old…
Anything will be really useful right now, much appreciated! The fish is very precious xx
Thanks xox