6th April 2000: Client phoned to say that one koi was
laying on the bottom, not eating and was generally lethargic. The fish
had been like this for several weeks but kept rallying around - could I tell him what the problem was? Lacking
the confidence of many in the aquatic trade I said no - at least not
without seeing the fish!
click on pictures to enlarge them
Large bacterial ulcer on koi with secondary Saprolegnia
fungus infection -
It was a small, shallow circular pond holding 2,200 litres (500 gal
UK) of water with goldfish and two koi. Everything looked fine. The koi
causing concern had been purchased at Christmas.
The koi was, as his owner said, laying on the bottom. However, there
was a mass of Saprolegnia fungus on one side, a small area of
fungus on the other side surrounded by inflammation and the caudal (tail
fin) was eroded. A skin scrape showed a higher than normal number of
skin flukes (Gyrodactylus). The other koi also had several skin
When we took the fish out of the water, the affected area was larger
than first thought. The main area of the lesion was badly infected with
a heavy growth of secondary fungus. There was extensive inflammation
around the lesion and an area of raised scales to the rear of the ulcer.
There was no skin covering the raised scales.
The infection may have been caused by the presence of skin flukes or
it may have been stress related. A significant factor was the koi being
purchased and put into a pond at the end of December - more so with the
relatively mild temperatures at the time. It is quite probable that the
combination of flukes, the stress of handling and transport together
with water temperatures around 10oC (high enough for
parasites but not for fish immune systems) was sufficient to start a
slow but progressive deterioration.
It was my opinion that given the severity of the infection that the
chances of survival were slim - probably between 20 - 50%
06/04/00 The affected areas were thoroughly debrided and
cleaned using povodine-iodine and covered with a water-proof paste
(Orabase) The koi was given an antibiotic injection (enrofloxacin) and
put in a treatment tank containing salt (3g/litre) and malachite green
07/04/00 The same treatment repeated
08/04/00 Saprolegnia had re-established itself in the ulcer,
which was now covered again in a fluffy white coat. The lesion was this
time cleaned with strong malachite green solution and sealed with paste.
The tank re-dosed with malachite. Unless the fungus can be eradicated
the ulcer will get worse rather than better
09/04/00 Fish removed from the hospital tank and sedated. The
wound is still clean and free of fungus. A third antibiotic injection is
given. The ulcer is lightly swabbed with povodine-iodine and
11/04/00: The fish's condition deteriorated overnight - it was
laying on its side and breathing heavily - it was euthanased to spare
any further suffering. No post mortem was carried out.
Clearly, the customers description of the problem was inadequate and
had I ventured a telephone diagnosis (a guess) I would have got it
As is so often the case, the situation was a lot worse when the fish
was examined out of the water. My guess is that initially there was
possibly a small lesion or perhaps a raised scale which could have been
topically treated. By just "leaving the fish to get better" -
this simple problem has progressed to a life-threatening situation that
is going to be time-consuming and expensive to treat - with no guarantee
that the fish will survive.
Buying fish in winter is a bad idea because of depressed immune
systems and cold water temperatures
The fish died unnecessarily because it had remained untreated for so
long while the problem got worse.