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Introduction to Freshwater Fish Parasites p1
Increased interest in fish culture has also increased awareness of and experience with parasites that affect fish health, growth, and survival. Information provided on this page is intended for the novice fish hobbyist as a guide to common parasites of freshwater fish. Identification of parasites and their basic treatment is included; however, this information should not be substituted for consultation with an experienced fish health professional.
NOTE: Mention of drugs or chemicals on this page in no way represents a recommendation for their use, nor does it imply that they are approved for use by the Food and Drug Administration or the Environmental Protection Agency.
Most of the commonly encountered fish parasites are protozoans. With practice, these can be among the easiest to identify, and are usually among the easiest to control. Protozoans are single-
Most of the protozoans identified by aquarists will be ciliates. These organisms have tiny hair-
The disease called "Ich" or "white spot disease" has been a problem to aquarists for generations. Fish infected with this organism typically develop small blister-
If only one parasite is seen, the entire system should be treated immediately. "Ich" is an obligate parasite and capable of causing massive mortality within a short time. Because the encysted stage (Figure 2) is resistant to chemicals, a single treatment is not sufficient to treat "Ich". Repeating the selected treatment (Table 1) every other day (at water temperatures 68–77°F) for three to five treatments will disrupt the life cycle and control the outbreak. Daily cleaning of the tank or vat helps to remove encysted forms from the environment. For more information, see Extension Circular 920, Ichythyophthirius multifiliis (White Spot) Infections of Fish.
Chilodonella is a ciliated protozoan that causes infected fish to secrete excessive mucus. Infected fish may flash and show similar signs of irritation. Many fish die when infestations become moderate (five to nine organisms per low power field on the microscope) to heavy (greater than ten organisms per low power field). Chilodonella is easily identified using a light microscope to examine scrapings of skin mucus or gill filaments. It is a large, heart-
Tetrahymena is a protozoan commonly found living in organic debris at the bottom of an aquarium or vat. Tetrahymena is a teardrop-
Identification of Tetrahymena internally is a significant but untreatable problem. A common site of internal infection is the eye. Affected fish will have one or both eyes markedly enlarged (exophthalmia). Squash preparations made from fresh material reveal large numbers (≥ 10 per low power field) of Tetrahymena associated with fluids in the eye. Fish infected with Tetrahymena internally should be removed from the collection and destroyed.
Trichodina is one of the most common ciliates present on the skin and gills of pond-
Ambiphrya, previously called Scyphidia, is a sedentary ciliate that is found on the skin, fins, or gills of host fish. Its cylindrical shape, row of oral cilia, and middle bank of cilia identify Ambiphrya (Figure 6). It is common on pond-
Apiosoma, formerly known as Glossatella, is another sedentary ciliate common on pond-
Epistylis is a stalked ciliate that attaches to the skin or fins of the host. Epistylis is of greater concern than many of the ciliates because it is believed to secrete proteolytic ("protein-
Capriniana, historically called Trichophyra, is a sessile ciliate that attaches to the host's gills with a sucker. They have characteristic cilia attached to an amorphous-
Treatment of ciliated protozoan infections
Several chemicals commonly used to control ciliated protozoans in freshwater fish are listed below for your convenience. As stated above, most ciliate infestations respond to one chemical treatment; however, fish that do not improve as expected should be rechecked and retreated if necessary. Over treatment with chemicals can cause serious damage to fish. The reader is also highly encouraged to read Extension Publication 673 (Mississippi State University), Calculation of Treatments, and UF/IFAS Fact Sheet VM-
Copper sulfate is an excellent compound for use in ponds to control external parasites and algae; however, it is extremely toxic to fish. Its killing action is directly proportional to the concentration of copper ions (Cu++ ) in the water. As the alkalinity of the water increases, the concentration of copper ions in solution decreases. Consequently, a therapeutic level of copper in water of high alkalinity would be lethal to fish in water of low alkalinity. Conversely, a therapeutic concentration of copper in water of low alkalinity would be insufficient to have the desired action in water of higher alkalinity. For this reason, the alkalinity of the water to be treated must be known in order to determine the amount of copper sulfate needed. The amount of copper sulfate needed in mg/L is the total alkalinity (in mg/L) divided by 100. For example, if the total alkalinity in a pond is 100 mg/L, the concentration of copper sulfate needed would be 100/100 or 1 mg/L. If you are unsure how to measure the alkalinity of your water, or have never used copper sulfate, contact your aquiculture Extension specialist for assistance. Never use copper sulfate in water that has a total alkalinity less than 50 mg/L.
Because of its algaecide activity, copper sulfate can cause dangerous oxygen depletions, particularly in warm weather. Emergency aeration should always be available when copper sulfate is applied to your system or ponds. Copper sulfate should not be run through the bio filter on a re circulation system as it will kill the nitrifying bacteria. If possible, tanks should be taken "off-
Potassium permanganate is effective against ciliates as well as fungus and external columnaris bacteria, and it can be used in a pond or vat. Multiple treatments with potassium permanganate are not recommended as it can burn gills. Aeration should be available when potassium permanganate is used because it is an algaecide and can cause an oxygen depletion. Potassium permanganate at the prescribed dosage (2 mg/L) does not seem to affect the nitrifying bacteria in a biological filter; however, ammonia, nitrite, and pH should be closely monitored following treatment. See also UF/IFAS Fact Sheets FA-
Formalin is an excellent parasiticide for use in small volumes of water such as vats or aquaria. It is not recommended for pond use because it is a strong algaecide and chemically removes oxygen from the water. Vigorous aeration should always be provided when formalin is used.
Used in proper amounts, salt effectively controls protozoans on the gills, skin, and fins of fish. This is an effective treatment for small volumes of water such as aquaria or tanks. Use in ponds as a treatment is generally not recommended due to the large amount of salt and high cost of treatment that would be needed to be effective. When using any treatment for fish, a bioassay (a test to determine safe concentration) should be conducted on a few fish before large numbers of fish are exposed. Fish species can react differently to various concentrations of the chemical; therefore, fish undergoing treatment must be monitored closely for adverse reactions. If the fish negatively react to treatment, the chemical should be flushed immediately from the system, or the fish should be moved to fresh water.
Identification of a Parasitic Problem
A common mistake of fish hobbyists is misdiagnosing disease problems and treating their sick fish with the wrong medication or chemical. When the chemical doesn't work, they will try another, then another. Selecting the wrong treatment because of misdiagnosis is a waste of time and money and may be more detrimental to the fish than no treatment at all. The majority of fish parasites can only be identified by the use of a microscope. If a microscope is unavailable, or the person using it has no previous experience with one, the diagnosis is difficult and questionable. Successful fish culturists learn by experience. Newcomers to the field need to learn the fundamentals of diagnostic procedures and how to use a microscope to identify parasites by attending short training courses. The following descriptions of common parasites can be used as references for understanding a professional diagnostic report or as a quick reference for the experienced fish culturist.