Ergasilus: Another parasite of the Axolotl to be aware of.
We had a problem this fall at the University of Manitoba Colony. By the
time we figured out what was going, we had lost eight males and about a
dozen jeuveniles. We finally understood what was happening because we
came in one morning to find one tank was swarming with thousands of tiny
little white specks. A few minutes with as microscope and some good
tropical fish health books and we tracked our culprit down. We were
dealing with Ergasilus, a parasitic cyclops type organism that
occasionally infests tropical fish.
The female Ergasilus is a parasite that attached itself to the gills of
fish and remains there. The attached female can survive for up to three
months shedding thousands of eggs during that time.The males and unmated
females are free swimming. They are barely visible to the naked eye as
tiny white specks that swim in a straight line at high speeds (unlike
Costia which swim erratically.) They collect along the glass of the
aquarium apparently nibbling on algae. The eggs are capable of lying
dormant for extended periods and can even survive drying. Obviously then,
Ergasilus is most likely to be a problem if you are using an undergravel
natural filtration type system.
Ergasilus infestation in axolotls is hard to spot in the earliest stages.
It can take weeks before the visibly free swimmer swarming stage is
reached and by then the gills of the axolotl are probably infested with
thousands of gravid females. Animals infested with Ergasilus are a bit
sluggish. They slowly loose weight in spite of eating well but otherwise
behaving normally. Some of the animals occasionally scratch at their
gills as if they are irritated. As the number of parasites increases, the
axoltols may also have occasional tiny fluffs of white on the gills but
when you check the fluff under microscope it appears to be simply shed
skin with no sign of parasite or infection. In our experience male
axoltols and are much more susceptible than female axolotls but this may
have been due to the male axolotls having been infected first. Just
before we spotted the free swimmers we had problems with some axolotls
suddenly dying after a period of subtle decline. We assume they acquired
a secondary infection through the gills and died of septic poisoning.
If you check the free swimmers under the microscope you will see the
typical cyclops type organism you can find in any pond, though somewhat
smaller. (They are hard to catch because they move so fast. Drain off the
water with a tissue so they have nothing to swim in in order to see hem
properly.) The body is tear drop shaped with a 'feathered' tail and two
prominant antennae on the head. They have a single red eye spot on top
between the antennae. As only attached females produce eggs, you will not
see any free swimmers with eggs sacs.
Most varieties of cyclops are not dangerous to axoltols and in small
quantities make an excellent addition to the diet of larvae. (One
cautionary note, according to the late Dr. Pieter Nieuwkoop, a diet
consisting solely of cyclops is not a good idea because clogging of the
digestive tract can occur due to the hard and brittle nature of their
exoskeleton.) Benign varieties of cyclops have many free swimming females
with two egg sacs. A lack of egg bearing females is the key to
ascertaining if the type you have is the parasitic variety.
We are uncertain where the parasite came from originally. We had two
members of our lab collecting samples of organisms from local ponds for
other purposes in the summer about two months before the outbreak. It is
possible some Ergasilus eggs may have ended up in an axolotl tank by
someone mixing equipment. Since Ergasilus is known to infect tropical
fish, it is also possible it came in via some feeder guppies we added to
our guppy breeding tank this summer but we have seen no sign of Ergasilus
in that tank.
Potassium permanganate, recommended by one fish care book, reduces the
numbers of free swimmers but does nothing about dropped eggs or females
attached to the gills of the axoltols. Salt water baths are useless at
all stages of the life cycle. In fact the free swimmers seem to like salt
water. A 1 hour bath in a dilute formalin solution is extremely effective
at killing attached female Ergasilus. (100 ppm for 1 hour.) Infected
axolotls frantically "paw" their gills and also turn and twist while
swimming as if greatly distressed for about ten minutes. After this they
settle down and stop the frantic activity. They cannot be returned to the
same tank because that tank will be heavily invested with free swimming
females seeking a host and eggs waiting to hatch.
We experimented with a variety of teatment to get rid of the eggs.
Cleaning and sterilizing the tank and adding new gravel does not work!
After several failures we found what seems to work well. To rid infected
tanks of both the free swimmers and eggs, remove the axolotls, and
abruptly raise the pH by at least two full units (7 to 9 for example). We
used common household bleach to do this. Let the tank stand with the
elevated pH for a week checking carefully for any free swimmers. The pH
will eventually return to normal and you should wait until at least two
more weeks, checking that the tank has been free of any sign of free
swimmers, have passed. After a three or four complete water changes the
animals can be returned to the tank. (You must treat the tank as if you
are establishing a whole new undergravel biological system, seeding the
bacteria from another tank, introducing one animal at a time, monitoring
for nitrate and ammonia and so forth.)We have been using tanks so treated
for about three months without any sign of the infection returning.
Obviously this is rather drastic treatment and if anyone has found a
better way to deal with Ergasilus I would appreciate hearing about it.
Natalie K Bjorklund
University of Manitoba Colony
Winnipeg, Manitoba, Canada