Dear Sir or Madam
I am hoping you can give me the benefit of your wisdom please as I have searched the Internet but cannot find a satisfactory explanation.
Out of about 25 Pond Fish (all healthy), one appears to be very lethargic and tends to sit on a shelf close to the surface of the pond.
As you can see from the attached photo, the fish is "nose down" with it's tail on the surface and is always in this position.
It does not "lay" in the deeper parts of my pond but always on the shelf however, when I get near the fish, it suddenly swims quickly away in a normal fashion as if there is nothing wrong.
The fact that it can always be found in the position in the photo is a bit concerning as there is no evidence of any growths however, at the base of the fish where the tail starts, there is a very red area.
I have used bacterial/ulcer additions to my pond but the fish seems utterly disinterested and stays away from the other fish.
This has been going on now for about 3 m or 4 months.
I estimate the fish to be about 12 to 15 years old.
I wonder if you can suggest anything please or whether to leave things alone as unless it has a personality problem or bad breath (haha), I can't understand why it doesn't readily mingle with the other fish unless, as I say, I disturb it.
Your replies will be well received and with thanks
I think you are already on the right track with your diagnosis and treatment.
When fish don't mingle with others, it is because they are sick. Even though Goldfish tend to be non-aggressive, they will pick at sick individuals.
If the red area is as it appears, either trauma or disease, the fish will need to be removed from the pond for effective treatment. It is hard to treat an individual in a pond environment because of the level of medication needed for such a large water volume.
Your water temperatures must be reasonably cold at the moment which is another reason to move the fish indoors if possible.
The redness could be caused by some sort of trauma, parasites or bacteria.
I would start with a mild salt bath for a week or so, (a teaspoon of un-iodised cooking salt per gallon), and also a bacterial treatment such as API Melafix or something similar.
If the redness is an ulcer, recovery is slow, hence the reason to bring the water temperature up slowly over several days to around 60-65F (16-18C).
If there is no improvement over that time, the underlying cause could be parasites. A Praziquantel based medication will deal with flukes or any protozoan parasites.