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Treating “ich” on freshwater and marine fishes.
General considerations:
Ich, in freshwater, is caused by the single-celled, protozoan called Ichthyophthirius multifillis. Thus the common name “ich”. In saltwater the ich parasite has a closely related organism called Cryptocaryon irritans. Both organisms cause whitish spots, called “cysts”, to appear on the bodies and fins of the infested fishes.
Like all parasite-caused diseases the fishes must be sufficiently stressed and susceptible to the parasite. Also, the parasites must be present in the fishes’ environment. It is not uncommon for an aquarium population to have a low-level of ich infestation present but not be showing any signs of the disease. Then, once a new fish is placed into the system it develops the disease.
Fishes can carry the parasite and not actually be diseased. These carriers can shed the parasite into a new aquarium into which it is placed. If the fishes in the new aquarium have never been exposed to the parasite, and they become stressed, they can develope the disease.
The parasite’s life cycle:
Both parasites have similar life cycles. Swarms of parasites (called “theronts”) break out of cysts (called “tomonts”) which may have laid dormant for several hours or days in the aquarium substrate or attached to the glass or tubing or other surfaces in the aquarium. The theronts swim in search of a suitable host. Once on a fish they penetrate the gill membranes and skin and began feeding. The feeding parasite causes a white spot which can be seen on the skin and fins. This is called a “trophont”. As the trophont feeds it enlarges and eventually breaks out of its cyst and falls to the bottom of the tank where the cycle starts all over.
The freshwater ich theronts are heat sensitive and raising the temperature several degrees above the normal aquarium temperature tends to kill them. In addition, increased temperatures enhance fishes’ immune responses. In saltwater, the ich parasite actually thrives at higher temperatures (>30ºC) and is inhibited at lower temperatures (<19ºC).
So, should the temperature be raised during treatment?
Given that temperature stress might have been a contributing factor in the start of the disease it is not logical to change the temperature again. Also, increasing the temperature, as many aquarists do, might actually increases the stress on the diseased fishes.
As the water temperature increases the dissolved oxygen content is reduced proportionately. For instance, ncreasing the temperature from 20ºC to 30ºC decreases the dissolved oxygen level by more than 17%. Additionally, the metabolic rate of the fishes also increases as the temperature goes up. This causes the fishes to consume more oxygen at a time when the increased temperature causes a decrease in the oxygen concentration.
Another consideration is that typically, long before one notices cysts on the body and fins of the fishes, the gills are heavily infested with the parasites. This gill involvement means that the fishes’ breathing is much more difficult. Therefore increasing the temperature works against the diseased fishes in several ways.
Raising the temperature, if done at all, should be done on the system before adding new fishes and before they are showing ich spots. This can be used as a method of prevention.
What about immunity and re-infestation?
As with most animals, fishes have a fairly well-developed immune system. Once a fish has suffered an ich infestation and survived, it is less likely to develope the disease again. This, of course, assumes the fish is not severely stressed at a time when the parasite is also present in the water.
The age and sex of a given fish can have an effect on its susceptibility. It is reasonable to expect juvenile fishes to have the greatest susceptibility. In addition, juvenile fishes have a much smaller ratio of body surface to body mass, and since the parasites feed on the body surfaces just a few parasites can easily kill a small fish.
A recent study done in Southeast Asia with tiger barbs, zebra danios and goldfish has found that some fishes can mysteriously impart their acquired immunity to ich to others of their own, as well as different, species. This is an interesting discovery, but not yet practical for managing the disease in store and home aquariums.
What’s the best drug to use?
There are three main drugs which have been found to be highly effective for treating ich in both freshwater and marine systems: malachite green (at 0.05 to 0.1 mg/L), formalin (at 15 to 25 mg/L) and a mixture of the two. The formalin/malachite green mixture has been shown to be more effective and less toxic than either drug used separately. Rid-Ich+ is a formalin/malachite green mixture and when used as directed produces a concentration of 15 mg/L of formalin and 0.05 mg/L of malachite green. Rid-Ich+ can be used with the so-called “scaleless” fishes, but should not be used on mormyrids (elephantnoses).
Keep in mind that whatever drug is used that it is not capable of penetrating the cysts. The drugs must be at full strength when the theronts are free swimming in the water. This is why it is important to observe and be aware of the cycle of appearance and disappearance of the spots on the fishes. The treatments (including the water changes) should be done when the spots have disappeared or decreased in number.
Copper (at 0.25 mg/L) is most often used in marine systems, but it too may be less effective and more toxic than the formalin/malachite green mixture. Copper should not be used on freshwater fishes.
We recommend that retailers follows the steps outlined on the back of this brochure. If there are any questions please call us at 816/842-5936 for assistance.
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