Formaldehyde 
A Remedy for Fish Infested with Parasites 
H. A. ROGERS, Pagosa Junction, Colorado 
saan two months ago we received 25 
goldfish from a reliable breeder who 
is also a personal friend. On arrival they 
seemed a little weak, but we attributed this 
to the long journey. Later indications 
showed an improper assimilation of food, 
which we thought no more than natural, 
the 
natural food of a pond to the concentrated, 
considering the change of diet from 
prepared fish food. In time we thought 
they would become accustomed to the 
change. 
After giving them frequent salt baths and 
keeping them isolated for ten days, we 
added a choice one to a colony of Japanese 
goldfish, every member of which had been 
Their 
provided with an aerator 
in perfect condition for three years. 
aquarium was 
which, even at low speed, had always kept 
the water thoroughly aerated even in the 
warmest weather. 
In a week’s time a beautiful, white, tri- 
pod nymph showed unfavorable symptoms, 
and, in spite of salt baths and special care, 
soon died. The symptoms, which were as 
new to us as they were alarming, spread to 
the entire colony, one after another dying 
until only two remained. The respiration 
of the fish went far above normal and they 
hung at the surface, gasping, as if suffering 
for air. Speeding up the aerator brought 
no relief. The fish became listless, carrying 
their fins close to the body, occasionally 
violently twitching the fins, or darting reck- 
lessly about among the rocks as if in great 
agony. 
bottom in a completely exhausted condition 
Later, they would lie around the 
for a day or two, when death would ensue. 
No discoloration or dissolution of scales, fins 
or tails having taken place; in other words, 
no outward signs of disease were visible, 
excepting a marked thinness of body just 
before death. 
In the meantime, the same condition had 
46 
developed among the new fish, one at a 
time dying until only ten remained. 
After 
every possible cause of the trouble which 
testing and finding untenable 
suggested itself to us, we came to the con- 
clusion that the disease must have been im- 
ported with the new fish, and that, inas- 
much as changing the water always gave 
temporary relief, it must be in the shape of 
a parasite whose numbers were greatly re- 
duced for a time by a change of water. 
A microscope of 250 diameters was next 
brought into service in the hope of dis- 
covering the cause and, lo! there it was, an 
leech-like 
which, by sudden and violent contraction 
active, vicious-looking, worm, 
and expansion of the body, struck out in 
all directions. 
The villain was quickly identified in a 
scientific volume on aquarium fishes as the 
Gyrodactylus elegans. It belongs to the 
group of flukes, having prehensile hooks at 
They 
burrow under the scales and infest the gills, 
one end and a sucker at the other. 
feeding upon the juices of their host. 
We were made heartsick by learning that 
among the uncertain remedies mentioned 
the most promising was to destroy the fish, 
disinfect everything, and start over again. 
By careful experiments my wife demon- 
strated that when the flukes were put into 
a solution of four drops of formaldehyde to 
a quart of water, death ensued in a few 
minutes. Here, then, was a hint of a 
remedy, worse, possibly, than the disease. 
I suggested that, as a desperate experiment, 
she place a patient in the solution. She re- 
ceived the suggestion as a joke, but, having 
one prominent characteristic of the true 
scientist, she is always just as ready to ex- 
plode a theory of her own as that of an- 
She said, therefore, 
You arrange for the funeral and I 
other. “well, here 
goes. 
will provide the corpse.“ 
She began, however, with a much weaker 
Much 
to our surprise, the fish swam around in it 
solution than that mentioned above. 
as though nothing unusual had happened. 
