After various domestic delays, I can now report on the outcome! See four images attached.
1. The first picture shows the growth as it was just before the operation. You can see that it is already significantly larger than when I first photographed it for this discussion thread. Clearly something needed to be done!
2. The second photo shows the setup on the kitchen table for the 'operation':
...... The blue bucket had 2 galls of tank water plus fish.
...... The white bucket had two galls of tank water plus (initially) 6 drops of clove oil.
.......The clove oil is the small bottle bought from ordinary local pharmacy as a dental treatment. When you take the cap off, it has one of those narrow tubes that allow you to count out a given number of drops - i.e. no need for an eye-dropper.
.......The jam jar was used to shake up the required number of drops of clove oil with a little tank water before adding to the white bucket.
.......Scalpel and scissors have a story attached to them - see below!
.......A little piece of cotton gauze about 5cm x 1cm (I think cotton wool would have done just as well)
.......Washing up bowl has in it a small plastic chopping board with the bottom 2/3 wrapped in a piece of towelling tied onto it, and all saturated with tank water (hence need for washing up bowl!).
.......Hygiene limited by omni-present tank water, but all non-tank items thoroughly washed before use. Scalpel and scissors brought to boil in a pan of water.
The fish was put in the white bucket with only 6 drops to 2 galls following a suggestion on another website that for safety one starts low and builds up. After 5 mins. fish still active, so shook up another drop of clove oil with water and added it to the mix, and stirred it around gently. And so on for about half an hour, drop by drop, always shaken up with water before being added to the bucket. When we eventually reached a total of 10 drops in the two galls, the fish finally became inactive. This all took about half an hour. This seems to confirm that the figure of '5 drops per gallon' quoted by some websites seems about right, and if I did it again, I'd go straight to 10 drops to minimise run-up effects on fish. But see Drop (unit) - Wikipedia, the free encyclopedia
for the wildly ambiguous meaning of 'a drop'. We need a sensible measure.
The original plan had been to support the fish on the towelling head down into the water, with the tail on the exposed end of the chopping board, and then to use the scapel. But in reality with the fish inactive and floating, it was much easier to leave the fish floating, hold the end of the fin that stuck out beyond the growth with my fingers, and just snip the fin with the scissors above the growth, though I found it tricky to be very accurate about this, so ended up cutting it closer to the growth than planned. Photo 3 shows the very unappetising growth.
To stop any bleeding from the two visible blood vessels, the cut end of the fin was then placed against the chopping board, the piece of gauze put on top of it, and my finger pressed on that (not too hard), with rest of fish floating free. The blood vessel down the middle of the fin became a little more pronounced - I guess it was the arterial supply so was under a bit of pressure. The blood vessel down the edge of the fin became much less pronounced - presumably the vein draining back into the fish.
After five minutes, I lifted my finger and the gauze, and checked for any blood loss. None visible, so fish lifted gently into blue bucket, and then into main tank over aerating block. Some slight signs of recovery quite quickly, but very dopey for at least 30 mins. Photo 4 shows tail the next day - you can see where the cut was by the two blood vessels.
Two days afterwards (today) the cut ends of the vessels show a slight red enlargement. Hopefully this is just the healing process, not due to some of the growth cells being left behind and taking off again, because it was cut too close to the growth. I'll keep you posted. Otherwise fish seems fine - and if anything a little more lively. I wonder if it will get its colour back?
I said that there was a story behind the scalpel and scissors. I went to my local craft shop to get a new blade for my craft knife, and found to my amazement that they sold Swann-Morton scalpel blades and handles that were absolutely identical to those in my undergraduate dissection kit that I had last used in 1960, and which was still buried away in a cupboard somewhere. So I bought some new blades, cleaned up the old handle, and bingo! Now what other high tech product will you find that hasn't changed one iota in 51 years!!! The dissecting kit also had my old dissecting scissors - still pretty sharp!
So hoarding old things does sometimes pay!