Oh dear he looks a bit worse for wear. I would have said it's an ulcer but to be honest it doesn't look as red as I would have thought if it was. It kind of looks like the skin has been rubbed off or something. Could that have happened somehow in your pond?

Or it could be an ulcer was caused by an injury and is now healing over again. How do the other fish look, any flashing or abnormal behaviour?

Congrats on the baby btw.

Thanks for the congrats...

All the other fish are very healthy.Having looked again it looks more like an injury, as if something has taken a chunk out. There's nothing in the pond that I can think of, no sharp rocks etc.Is there anything that lives in a pond that would attack a fish that size? - it's about 10cm (although as it's a Comet, a lot that is tail)The pond is partially netted after an unfortunate heron incident a few months back.

well, that looks like a real bad wound,its not a heron wound, and I would think that fish is feeling rather sore! I would be inclined to treat that while the temps a fine, I doubt that fish can cure it by itself eb end of summer, the wound is too big, try some ulcer treatment, or dab a bit of potasium permanganate (about 5 garins and little water) with a q-tip, that will quaterise the wound and kill and bacteria it might have on it, but dont be supprised if you do lose the fish, it needs to be fully cured before onset of winter, but probebly will if you dont treat it.

I would be tempted to treat the water with medifin just to help with healing process. I think this would help.
Steve

Any chance of baby pics?

Steve... that wound is to big for a pond treatment, needs hands on treatment to tackle it, but medifin would be ok to add afterwards as a back up, medifin and the likes are ok for small sores and wounds etc, but wont do much for one as big as that on that size fish.