Ich: An old cure for an old disease
By Terry Ranson
From Vol. 2, No. 2, The Newsletter of The Tri-State Aquarium Society, January
Probably the most common disease among fish is ich. But, what do you really know about
Ich is short for the name of a ciliated protozoan of the genus Ichthyophthirius.
Ich is usually present all the time in aquaria in small numbers, just like germs are in
the air we breathe. However, when a fish suffers from extreme stress, such as a sudden
drop in temperature, its resistance is lowered and it becomes vulnerable to diseases. Ich
outbreaks also occur after the introduction of new fish to an established aquarium.
Ich is free-swimming until it attaches itself to the skin of a fish. Under a
microscope, the organism is easily seen and identified, even under low magnification. It
looks like a round, rolling mass. According to John Gratsbek, et al, in the book
Aquariology, The Science of Fish Health Management (Tetra Press), ich is one of the few
fish parasites completely surrounded by cilia. The organism's U-shaped nucleus is often
visible under a microscope.
Once the free-swimming ich reaches a fish, it attaches to the outer layer of the skin
of the host fish. The ich organism then forms a tough outer shell, or cyst, while
it feeds on the fish's bodily fluids. This encysted stage, called a theront,
grows large enough to be seen with the naked eye. Each theront appears as a tiny white
spot on the fish. Severe ich infestations make fish appear as if they are covered with
salt. After the theronts grow to a certain size, they break through the skin and drop off
the fish. As they fall, they attach to the bottom or sides of the aquarium, or to plants,
gravel, decorations, tubing or any other stationary object. Theronts then begin their
reproductive stage, and are then called a trophozoite, also known as a trophont.
The attached trophozoites then begin producing the infective, free-swimming stage.
Hundreds more free-swimming ich organisms, called tomites, can arise in less than
a day and a half, and they in turn re-infect the fish in your aquarium.
In nature, ich is not much of a problem. There are large numbers of fish to which
tomites can attach. And with the greater amount of water volume, it's likely that many ich
organisms do not even find a host. However, in a closed system like an aquarium, ich
re-infects the same fish over and over, resulting in severe infestations. That's why it
can be such a problem.
While ich is encysted on the fish, no medicine can affect it. But once it's
free-swimming, it can be killed. Since the life cycle of ich takes at least three days at
80 degrees to complete, ich must be treated for at least four days. I prefer to treat for
Although many aquarists use rather harsh chemicals to kill off Ich, I prefer
more natural methods:
- Ich dislikes warm water, so I immediately bring the water up to 85-88 degrees.
- Since warm water cannot hold as much oxygen as cool water, I also increase the aeration
by adding air stones. Another reason for added aeration is that ich infects the gills of
fish as well as the outer skin. We only see ich on the skin of fish, and assume that's
what's making them so sick. But my personal belief is that gill infestation by ich is the
main cause of suffering and death in aquarium fish. I believe this damage to the delicate
gill tissue suffocates fish, which either kills them outright or leads to lethal secondary
infections. An increase in dissolved oxygen brought about by vigorous aeration may mean
the difference in life or death to your fish.
- Along with a temperature change and added aeration, I usually add about one teaspoon of
canning & pickling salt per gallon to the water to help the fish recover from the
stress caused by the disease by reducing osmotic pressure, enabling the fish's own immune
system to fight back. Salt is also harmful to ich.
- Water changes are extremely important in fighting ich outbreaks. Using a gravel washer,
I do a 50 percent water change on a daily basis. This eliminates a great number of
trophozoites and tomites from the aquarium.
- While I prefer not to use chemicals to treat any disease, developments over the past few
years have left me little choice. The ich we contend with today are particularly virulent
strains because, in my opinion, so many hobbyists, and, more importantly, pet shop
owners/employees, have used chemicals and antibiotics instead of good hygiene to treat
disease. What I refer to as hygiene is simply hard work: i.e. water changes, heat, added
aeration and salt. When that is insufficient, I use Rid-Ich, which is a commercially
available medicine consisting of zinc-free malachite green and formalin. I've found this
to be highly effective in treating ich.
If your fish recover from ich, they may not get it again. There is evidence that fish
become resistant to ich after they survive the initial infection, so fish which recover
from an ich infestation should be less likely to contract the disease at a later time.
However, I would still recommend a three-week quarantine period for all newly purchased