As winter approached the pond's floating plants (water hyacinths) would be killed off and needed to be discarded. Being of Scottish heritage I decided to save them by putting them in my indoor 50 gallon hospital tank which was otherwise empty, figuring I could put them back outside in the spring.
After a couple of weeks I noticed some sperm-like creatures moving all over the tank as well as a bunch of snails (I never saw any snails in the pond). I took a magnifying glass to the wall of the tank and drew a picture of what I was looking at.
Then I hit the books to see if I could identify what I had. Sure enough I found it.
How would you like to have this baby all over your lungs (gills). Ergasilus is a parasitic copepod. Those leg like appendages are really egg sacks. Ergasilus is sometimes called "gill rot".
They had survived several "ich" treatments of 15 PPM (parts per million) of 37% formaldehyde and .05 PPM malachite green which was the accepted treatment for "ich".
Then I purchased some "Trichloracide/Trichlorfon" from Argent Chemical Laboratories through a supplier. Much to my surprise there was absolutely no indication on the bottle of the strength of the mix. The supplier said he didn't have a clue. So I checked out Argent's web site, which showed an 80% strength for a much larger quantity available only overseas.
Once again I treated them to the above formaldehyde/malachite green combination with a 1 PPM "Trichloracide" kicker (based on the assumed 80% concentration) which didn't seem to touch the Ergasilus at all. After checking with Argent and going round and round, they wouldn't say the exact concentration of their "Trichloracide" but indicated it might be as low as 0.5%. When I told them that was a useless concentration they said they didn't want to kill any fish. When I complained that it also wasn't killing the Ergasilus they replied that this was a safe product.
I consulted the "KOI KICHI" book which mentioned a 5 times greater concentration of malachite green (0.25 PPM), increasing the 37% formaldehyde from 15 to 25 PPM at 70°F, and adding 0.3 PPM of Masoten (Dylox or Trichlorfon). After I located a new and reliable source for the Dylox I hit them again. By-the-way, Dylox does a real job on invertebrates, i.e., snails.
That combination did the trick although it took 24-36 hours to get rid of them. I repeated the treatment according to the recommendations in "KOI KICHI". The Ergasilus were now gone along with the troublesome snails.
Knowing the plants had come in from the pond and therefore Ergasilus had to be there too, I hit the pond with the same treatment, again repeating it according to the recommendations in "KOI KICHI". If I had not brought the hyacinths in I never would have known about the Ergasilus.
Then some interesting events happened. Most if not all of the KOI and goldfish in the pond started flashing on the bottom something they never did with the other treatments. I chose to interpret this as being caused by the Ergasilus releasing their grip on the gills, although it really could have been caused by any number of other sources. Then after a few days one of the KOI developed a massive fungus attack which was on its gill plates, head and side.
This apparently is caused by fungus spores attacking the open wounds left by parasites that are killed off. Interestingly, this happened right after a 15% water change which reduced the concentration of the remaining medication.
That Koi became very weak and I decided to bring him into the warmer hospital tank. The fungus was bad, but cleared up in a day after another malachite green - formaldehyde - masoten treatment.
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