Treatment of White-spot disease (Ich) in fishes
Because not all stages in the life cycle of Ichthyophthirius are affected by treatments, multiple treatments must be administered to catch individual Ichthyophthirius organisms in the vulnerable stages of their life cycle.
For example, during the first day when a chemical is added to the water to kill Ichthyophthirius, only a certain percentage of Ichthyophthirius organisms will be susceptible to the chemical. Two days later many of the surviving Ichthyophthirius organisms, which were embedded in the skin of Ornamental fishes, will be entering the vulnerable stage of their life cycle; chemical treatment on this day will kill these susceptible organisms. In order to catch all the Ichthyophthirius organisms in a treatable stage, from three to seven treatments might be needed depending on water temperature. Treatment effectiveness should be evaluated by a fish health professional after the third treatment to decide whether to continue with the treatment schedule. Mortality rates should be observed, and samples of fish from the infected pond should be examined for Ichthyophthirius under a microscope. The spacing of treatments varies with temperature. Some fish health professionals believe treatments should be applied every day, even in cooler weather, instead of skipping days in between. Ichthyophthirius appears to have a distinct temperature range in which it is infectious. It has been observed that temperature changes of 15 degree F or more above or below the temperature at which an Ichthyophthirius case is detected will end the disease episode regardless of the number of treatments made.
In some cases, one or two treatments may be all that is necessary to buy time for the Aquarium fish until such a temperature change occurs. The U. S. Food and Drug Administration has approved the use of formalin to control Ich on trout, salmon, catfish, largemouth bass and bluegill. FDA has also given copper sulphate (CuSO4) and potassium permanganate (KMnO4) deferred status, which means that these treatments may be used without legal prosecution, but they may lose deferred status if evidence is found of any danger to the human consumer. No other chemicals should be used to treat Ichthyophthirius Ich on food fish. Of the three therapeutants, copper sulphate is the least expensive.
Treatment rates for various chemicals are described below. Adding extra chemical for good measure may kill or stress the fish being treated, while using less than the required therapeutic dose may not be effective in killing the parasites that are causing the fish to die.
Formalin is a solution of 37 percent formaldehyde in water with 6 to 15 percent methanol added as a preservative. It should be stored at temperatures above 40 degree F.
Formalin can be used as a bath treatment for up to an hour at 125 to 250 parts per million (ppm) (4.4 to 8.8 milliliters per 10 gallons; 32.8 to 65.5 milliliters per 10 cubic feet). The treatment rate should not exceed 167 ppm on warm water fish when temperatures are higher than 70 degree F (21 degree C), or on trout and salmon when temperatures are above 50 degree F (10 degree C). Tanks should be flushed with clean, aerated water after an hour, or sooner if fish show signs of stress. Formalin is used as a pond treatment at 15 to 25 ppm. This would be 4.5 to 7.5 gallons of formalin per acre-foot (an acre of water 1 foot deep).
Formalin should be applied evenly throughout the pond. Formalin should be handled very carefully because its fumes are dangerous and can damage the mucosal lining of the nose and throat.
Copper sulphate (CuSO4)
Copper sulphate (CuSO4), sometimes called bluestone or just copper, is the most affordable chemical available for treating Ich. Copper sulphate is used as an indefinite treatment (I.e., applied to the water and allowed to remain without subsequent dilution of the treatment). The treatment rate is determined by the total alkalinity concentration of the water being treated; the treatment rate of copper sulphate in ppm is equal to the total alkalinity divided by 100. For example, if the total alkalinity of a pond/ aquarium water/ tank were 85 ppm, then the treatment rate for copper sulphate would be 85/100 = 0.85 ppm. In a pond, the pounds of copper sulphate needed in this example would be:
Acres x average depth in feet x 0.85 ppm CuSO4 x2.7 pounds of CuSO4/acre-foot/ppm = lbs. CuSO4
In a tank measured in gallons, the grams of CuSO4needed (when total alkalinity is 85 ppm) would be:
Gallons x 0.85 ppm CuSO4 x 0.0038 grams CuSO4/gallon/ppm = g CuSO4
In a tank measured in cubic feet, the grams of CuSO4 needed (when total alkalinity is 85 ppm) would be:
Cubic feet x 0.85 ppm CuSO4 x 0.0283 grams CuSO4/gallon = g CuSO4
Potassium permanganate (KMnO4)
Potassium permanganate (KMnO4) (Often referred to as Potassium) is an oxidizing agent that oxidizes organic materials in water, including protozoan parasites or external bacteria living on the surface of fish. It is usually used as an indefinite treatment in ponds at a rate dependent on the amount of organic material in the water. Two (2) ppm of KMnO4 is the minimum dose required to be effective against external parasites such as Ich, while waters rich in nutrients with a heavy algal bloom need a greater amount of KMnO4 for an effective treatment. (An author is aware of one case where 20 ppm KMnO4 was needed to reach an effective treatment level.) A potassium permanganate demand test is often used by aquatic biologists and Extension specialists to determine the most effective, but safe, treatment rate.
A traditional technique for deciding on the correct dose of KMnO4 is to add 2 ppm at a time until a wine-red color is attained in the water, and this color should persist for at least 8 hours to give an effective treatment. The person applying the potassium permanganate should make sure that the chemical fully dissolves during the application so that an accurate judgement can be made on the color in the water. On at least one occasion the water seemed to not turn red after several applications of 2 ppm of KMnO4, then suddenly the water turned an intense red color when the undissolved KMnO4 dissolved all at once, killing every fish in the pond. Usually, however, this technique of applying 2 ppm at a time works well. A bath treatment of KMnO4 at 10 ppm for 15 to 20 minutes (about a level 1/2 teaspoon of KMnO4 per 100 gallons of water) is an effective short-term treatment. Water should be readily available to flush the tank quickly if the fish show any signs of stress. The following example shows the calculations for the amount of KMnO4 to add to a pond that needs 2 ppm KMnO4. 1 acre-foot x 2 ppm KMnO4 x 2.7 lbs. KMnO4/acre-foot/ppm = 5.4 lbs. The amount of KMnO4 to use in a tank with 300 gallons of water (before adding fish) to attain a 10 ppm concentration for a 15- to 20- minute bath treatment would be calculated as follows: 300 gallons of water x 10 ppm x 0.0038 grams KMnO4 /gallon/ppm = 111/2 grams KMnO4
Salt (sodium chloride; NaCl)
One of the best treatments and preventives for Ich has been 2 to 3 parts per thousand (ppt) of salt indefinitely. This is usually a very effective treatment for tank and recirculation systems but is not cost effective for ponds.
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