Ergasilus and the Axolotl

umbjork1 at cc.UManitoba.CA umbjork1 at cc.UManitoba.CA
Thu Mar 13 09:41:21 EST 1997

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

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