OJ was my first big koi. Sadly he got struck by the ulcer disease that hit my fish this last summer. He mostly recovered from this but aeromonas bacteria continued to eat away at his gill cover - or operculum. I thought that this had stabilised, but then noticed that it had in fact progressed and he was showing increased signs of illness.
The hole can also be a sign of tuberculosis - which is transmittable to humans, so one has to be careful. But given the history I am pretty sure it is bacterial.
More on the problem at:
So OJ has been caught and is in quarantine. Here he is. Looks miserable, hey?
The red water visible through the side of the quarantine container is that colour due to a dose of Potassium Permangante. This is to kill the external nasties. Today he begins a sequence of Baytril antibiotic injections. Which is a treatment I hate administering. See this old blog entry on the procedure.
Once I have got him right, he will sport the hole for the rest of his life, together with the funny mouth he now has after recovering from his previous ulcer.
My plan to ease his troubles is to super-glue a fish scale over the hole. This will enable him to seal his gills as he normally would to regulate the pressure as he breathes. It's not essential, but closer to normality.
On the subject of koi, I went to the SAKKS National Koi Show at Cresta this weekend. It was something to behold. There were over 50 porta-pools containing fish in the competition. In addition, each dealer had pools with fish for sale. Take a look at the size of this brute who was in the competition:
I couldn't resist the temptation and bought two beautiful fish at pretty good prices.