Disease Management

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The following information is designed to provide a guide to disease management in a commercial facility. This information is a guide only, and should be used in conjunction with other information from experienced, qualified sources.

This information is not designed to be a complete or comprehensive disease manual, but could be used to help growers develop their own disease manual. Always check the regulations for aquaculture in your jurisdiction, and if any chemicals you plan to use are approved for use on fish in your jurisdiction.

Pictures of almost all pathogens mentioned here can easily be found on the internet. These pictures should be included in on-site hard copies of disease manuals to aid staff in the interpretation of images seen under a microscope.


Silver Perch Aquaculture Research and Development

Much of our knowledge regarding perch has come from researsh done on silver perch. Silver perch (Bidyanus bidyanus) is an Australian native freshwater fish that is endemic to the Murray-Darling River System. It is a high quality, white-fleshed finfish with high levels of omega oils that has long been recognized as having potential for aquaculture. Originally fingerlings were used for stock enhancement in impoundments, and sold for stocking farm dams; in 1982 the sale of native fish was transferred to commercial hatcheries. Research into grow-out commenced at the Grafton Aquaculture Centre in 1990, and demonstrated that silver perch is an excellent species for culture in earthen ponds with high survival rates (> 90%), fast growth rates (2-5 g/fish/day) at high stocking densities (20,000/ha) leading to high production rates (10 tonnes/ha/year). Between 1996 and 2005, there were research projects into nutrition and diet development, feeding strategies, as well as, tank and cage culture, and production in tank-based re-circulating aquaculture systems. Apart from temperature tolerances, and growth rates, jade perch are very similar to silver perch, therefor, almost all information referring to silver perch, can be applied to jade perch.

Infectious diseases

In Australia the number of known pathogens and infectious diseases of silver perch had increased from 4 in 1983 to around 20 by 2007. Protozoan parasites Ichthyophthirius multifiliis (causes the disease white spot or ichthyophthiriosis), Chilodonella hexasticha (chilodonellosis), Trichodina sp. (trichodinosis) and Ichthyobodo necator (ichthyobodosis), and the monogenean gill fluke, Lepidotrema bidyana, accounted for around 80% of all records. White spot and chilodonellosis are acute diseases that can cause high mortalities if not diagnosed and treated promptly. Silver perch are susceptible to two fungal diseases, winter saprolegniosis (colloquially called winter sap or winter disease) and epizootic ulcerative syndrome (EUS or redspot) caused by Aphanomyces invadans. Bacterial diseases of silver perch include columnaris, tail (or fin) rot, streptococcosis, mycobacteriosis and aeromonad dermatitis. No viral diseases were recorded, but the epizootic haematopoietic necrosis virus (EHNV) kills silver perch under laboratory conditions and so is a potentially serious pathogen.

Winter saprolegniosis

The causative agent of winter saprolegniosis was identified as the pathogenic fungus, Saprolegnia parasitica. Detection of the disease in the initial stages is difficult in characteristically turbid ponds, where fish are difficult to see and feeding activity is reduced in winter. Heavily-infected fish often swim slowly near the surface and edges of ponds, with patches of fungus clearly visible on de-pigmented areas of the skin and gills. Large silver perch (> 180 g) are more susceptible than smaller fish, and if untreated, winter saprolegniosis can cause 100% mortality. Most outbreaks commenced at water temperatures below 16°C, and rapid decreases in temperature (e.g. 4° - 5°C in 5 – 7 days) to below 10°C following cold changes during winter were associated with onset and severity suggesting that suppression of the immune system is involved in the initiation of winter saprolegniosis. Pre-disposing factors include: infestations of ecto-parasites; damage to fish from handling during partial harvesting of ponds; high stocking densities and biomasses (> 20,000 fish/ha and 10 tonnes/ha); high organic loads; and poor water quality. Recommended management actions to assist in the prevention and control of winter saprolegniosis are: reduce fish biomass to < 6 tonnes/ha; ensure fish are free of ecto-parasites; do not over-feed; maintain good water quality; avoid partial harvest; and treat harvested fish in tanks with a continuous bath of salt (2 g/l) and formalin (30 mg/L).

White spot

White spot is caused by the ciliate protozoan Ichthyophthirius multifiliis. It is a common and acute disease of freshwater fish through-out the world, and causes significant mortalities and economic losses in many industries. Perch are susceptible to white spot, and outbreaks may occur at any temperature. White spot is a difficult disease to treat, particularly at low water temperatures because of the complex life cycle of I. multifiliis. Experiments were carried out at Grafton Aquaculture Centre to determine: (i) the efficacy of copper and formalin in treating white spot; and (ii) the depletion rates of these chemicals. Copper (as copper sulfate) at concentrations of 0.1 – 0.2 mg/L controlled white spot, but higher concentrations of 0.25 – 1.0 mg/L were toxic to silver perch, and 0.05 mg/L was ineffective. Formalin at a concentration of 30 mg/L controlled white spot, but 20 and 10 mg/L did not completely controlling the disease. In earthen ponds containing silver perch, copper (0.2 mg/L) and formalin (30 mg/L) were depleted to or below therapeutic concentrations within 24 and 48 h post-treatment respectively. Using these data, new treatment regimes for copper and formalin involving applications daily or on alternate days were developed and validated. Outbreaks were successfully controlled using either chemical at costs of $486.00/ha/day for formalin and $68.34/ha/day for copper (as copper sulfate). A continuous salt (NaCl) bath of 2 g/L was effective in controlling white spot and preventing saprolegniosis. This treatment is recommended in aquaria, tanks and re-circulating aquaculture systems, but not in ponds because of the large quantities of salt required, potential for accumulation and detrimental environmental effects of saline water.


This is an acute disease of perch caused by the ciliate protozoan Chilodonella hexasticha. It can cause high mortalities within several days unless diagnosed and treated promptly. Fortunately, it is relatively easy to treat using formalin (30 mg/L) in ponds, or salt (10 g/L for 1 h) or formalin in tanks.

Gill flukes

Monogenean gill flukes are common fish parasites with strict host-specificity and a non-pathogenic nature which reflects a highly developed relationship to their hosts. The fluke infesting silver perch is Lepidotrema bidyana. Mortalities from infestations of gill flukes are generally low (< 5%), and light infestations do not cause problems. However, heavy infestations can cause gill damage, impair respiration, reduce appetite and growth, and predispose fish to bacterial and fungal infections. Infestations can be controlled in ponds and cages by formalin (30 mg/L) or trichlorfon (0.5 mg/L; Lepidex®), but eggs are resistant to formalin and trichlorfon, and three consecutive treatments 7 – 21 days apart are needed to control infestations. In tanks, 0.25 mg/L trichlorfon (Lepidex® 500) is sufficient to control flukes.

Chemicals (NOTE THAT CHEMICAL REGISTRATION CHANGES FROM TIME TO TIME. READERS OF THIS INFORMATION MUST SEEK UP-TO-DATE INFORMATION.) Always check the regulations for aquaculture in your jurisdiction, and if any chemicals you plan to use are approved for use on fish in your jurisdiction.

Chemicals play an important role in aquaculture, by facilitating many operations such as handling fish, control of reproduction, management of water quality, promotion of plankton blooms, sterilisation of facilities and equipment, and control of plants and diseases. Chemical therapeutants are essential in controlling some infectious diseases, particularly acute diseases that can cause high mortalities if not treated promptly. In Australia, the Australian Pesticides and Veterinary Medicines Authority (APVMA) regulates chemical use in aquaculture, and only chemicals that are registered or permitted can be used legally. (Always check the regulations for aquaculture in your jurisdiction, and if any chemicals you plan to use are approved for use on fish in your jurisdiction.) Chemicals that must not be used in Australia on food species include, but may not be limited to, malachite green, chloramphenicol and nitrofurans. The use or detection of illegal chemicals will jeopardise the future of an individual farm, a species, an industry, and aquaculture in general. Care should be taken with the use of chemicals, and directions and recommendations must be followed.

Health management

Health management is a concept of dealing with fish health by providing general environmental and culture conditions that reduce the incidence and severity of diseases, leading to efficient and economic production of fish. The old saying “An ounce of prevention is worth a pound of cure” is very applicable to perch farming. Health management commences with the selection of a good site and encompasses all aspects of the production cycle by combining a well-designed farm with Good Aquaculture Practices to minimise stress and health problems, and to optimise survival, growth, food conversion, and production. Site selection, design and operation of farms, water quality monitoring and management, husbandry and production techniques, and nutrition and feeding, all these aquacultural practices form the basis of good health management. 

Comercial fish growers will increase profits, through, knowledge of perch diseases, developing their skills in using microscopes and diagnosing and treating diseases. Know need for regular monitoring of fish for disease and for improved health management.





On arrival all staff must wash hands up to elbows before commencing work. Foot wash must also be used before commencing work. All staff are responsible for visitors and must ensure they do not enter the hatchery modules before using foot wash. Visitors must also wash hands if they are likely to touch any tanks. Visitors must not place hands in tank or on tank surfaces unless necessary.

Many diseases can be avoided by always handling fish in a 2ppt salt solution.

Nets should be restricted to the batch or unit of fish being handled. This may be limited to a tank or pond of fish. Before being used again each net should be sterilised, including the handle, by the appropriate method. (Develope a management for appropriate method.) Hands must be washed before moving between a batch or unit of fish. Hands and feet, (foot wash tray) must be washed before moving between each hatchery module or moving from hatchery to ponds or ponds to hatchery.

Hands should be kept away from tanks and tank surfaces unless you are working on the individual tank.

New Fish

If new fish are introduced they should be held in Quarantine for an appropriate period. Provide to management for instructions for staff.

Quarantine fish with disease

Where a disease has been identified in any tank/pond, the tank/pond should be marked with a “Q”, for “Quarantine.” Tanks/ponds marked with “Q” must be treated as an individual units. All utensils must be restricted to individual tanks/ponds marked with “Q”. Hands must be thoroughly washed after working on these tanks or ponds. All utensils must be placed in chlorine bath


Ozone is an effective tool to control disease.

See appendix 1 for ozone information

Hygeine Procedures

On arrival all staff must wash hands up to elbows before commencing work and use the hand sanitizers located at four strategic points around the hatchery complex. Foot wash must also be used before commencing work. All staff are responsible for visitors and must ensure they do not enter the hatchery modules before using foot wash. Visitors must also wash and sanitize hands if they are likely to touch any tanks. Visitors must not place hands in tank or on tank surfaces unless necessary.

All staff and visitors must use hand sanitizers and foot bathes between areas of an aquaculture complex. All nets, (Including their handles.) and equipment used in tanks/ponds should be sterilised in a chlorine solution between uses. Wherever possible, nets and equipment should only be used in one tank or batch of fish and should not be used in other tanks without being sterilised in a chlorine solution. Hands should be kept away from tanks and tank surfaces unless you are working on the individual tank.

All the concrete floors in the aquaculture complex should be washed with a chlorine solution every two weeks to minimise build up of pathogens.

Quarantine Procedures

Where a disease has been identified or suspected in any tank/pond, the tank/pond must be marked with a “Q”, for “Quarantine.” Tanks/pond marked with “Q” must be treated as individual units. All utensils must be restricted to individual tanks/pond marked with “Q”. Hands must be thoroughly washed and sanitized after contact with these tanks/pond. All equipment should be sterilised in chlorine after use. Management must be informed when a tanks/pond are to be marked as a quarantine tank/pond. A record should also be made in the disease log. All water that is drained from the tank/pond should be treated with chlorine, or isolated for the appropriate period. Water should only be drained where necessary to maintain water quality in optimal parameters in the tank/pond. If possible, fish should be moved to the quarantine area to reduce the likelihood of spread of the disease

Disinfection Procedure

After the fish are removed from a infected tank/pond (the water should not be removed to remove the fish), the tank/pond and the water in it needs to be sanitised. This can be done by adding a high dose of chlorine to the tank/pond, or isolating the water for the appropriate period*. All filters and air stones should remain in the tank for this procedure, with the air turned off. Chlorine should be left in the tank for a minimum of 24 hours. After this time the water should be emptied and the tank and filter rinsed to remove residual chlorine. The tank should then be left to dry out completely before filling.

Standard procedure for the restarting of ponds is to empty out all the water and to let it dry in the sun until the mud is cracked. The pond is limed and refilled. If a disease is present in a pond before it is emptied, the pond water should be treated with a high dose of potassium permanganate (eg greater than 10ppm) before the pond is emptied. Depending on the disease suspected, the pond could also be treated with Hydrated lime.

* appropriate period.  Some pathogens cannot survive without a host animal. Therefore, the appropriate period would depend on the pathogen identified.

Emergency Disease Outbreak Procedure

Any disease outbreaks must be reported to management. Disease outbreaks include abnormal behaviour, abnormal number of mortalities or sick looking animals. If it is suspected that it could be a Notifiable disease, (Where this applies.) then samples must immediately be sent to the relevant authority, (Where appropriate.)  If the disease is identifiable, then treat accordingly. If the disease is unidentifiable, then send sample away for testing.

Any suspected tanks or ponds with suspected disease should be quarantined and marked with a large Q and state suspected disease. This makes it obvious to other workers that a disease is or may be present. Record disease outbreak in disease log, noting any treatments and successfulness of treatments. Ensure treatment is suitable for the type of fish as certain treatments can only be given to ornamental fish due to government regulations on the use on chemicals on food fish. If the first treatment does not work, then consider alternative treatments or dose rates. If a successful treatment cannot be found, consider euthanizing fish and disposing off carefull.

Bacterial infections

Fin rot, tail rot, mouth rot, body rot. (Columnaris) Columnaris is a common bacterial infection. The bacteria causing this infection are part of the natural fauna. It is commonly found in water, soil, and even on the skin of healthy fish.

Columnaris prevention is relatively easy. This bacterium usually does not cause damage to fish because the mucus coating on the fish is their natural protection from bacterial infections. Damage to the mucus allows the bacteria to reach the tissue of the fish. Handling of fish is a common cause of damage to mucus.

Unnecessary handling of fish should be avoided. When it is necessary to handle the fish for harvesting, sorting, grading and packing, the process should be done as quickly as possible. Crowding should be avoided. Handling fish during high temperatures should be avoided. Correct choice of nets and not handling too many fish at a time will reduce the damage to the fish’s mucus.

Treatment: If a minor infection of columnaris occurs remove the infected fish, and hold the fish in about 3 grams per litre salt solution. Maintain the highest water quality possible. Frequent water changes should be made. If this treatment is not effective the salt can be increased as appropriate to the species. If the infection cannot be managed in this way treat with oxytetracycline, (Usually under veterinary supervision.) can be very effective. Do not handle the fish until the infection has passed.

Columnaris in ponds can also be treated with potassium permanganate* at a concentration of 2 parts per million (ppm). This concentration will cause the water to be wine red in colour. If the colour fades to yellowish-brown in less than 4 hours, it may be necessary to retreat. In a tank, potassium permanganate can be used at a slightly higher concentration, but fish must be observed during the treatment. As much as 10 ppm can be used for a short term bath of 30–60 minutes. Fish must be watched closely, and water should be changed immediately if they show signs of stress. Following treatment, a complete water change is necessary to avoid gill damage. This method should be used during periods where outbreaks are occurring regularly. 

Protozoal Parasites  

The majority of the fish parasites which cause disease in fish include protozoal parasites.  Typically, these parasites are present in large numbers either on the surface of the fish, within the gills, or both.  When they are present in the gills, they cause problems with respiration and death will commonly occur when additional stressors are present in the aquatic environment.  Protozoal parasites on the skin, fins or scales only, (i.e., not affecting the gills) usually do not result in death, unless they are accompanied by a secondary bacterial infection, usually columnaris. The more common protozoal parasites are listed below. (Columnaris treatments see above.)

Ichthyophthirius multifilis:  Although rarely seen in areas of higher water temperatures, this is probably the most common parasite of all fishes.  The common name for this parasite and disease is “Ich” or “white spot”. Outbreaks of white are probably due to introduction of the parasite with new fish, or on employees hands.

The mature parasite reaches approximately 1 mm in diameter and is commonly observed in the skin and fins as white spots, (Like grains of salt.) hence the common name.  The mature stage of the parasite has a large “horseshoe” shaped nucleus, and the entire surface of the parasite is covered in cilia.  This organism is an obligate parasite which means that it cannot survive unless live fish are present.

The life cycle of this parasite is direct, but is spent, in part, off of the host.  The mature parasite is within the epidermis of the host, until it leaves the fish, encysts and divides to produce many host-seeking tomites.  The tomites penetrate the skin and gills of the fish to complete the life cycle.  The life cycle is temperature dependent with a shorter life cycle occurring at warmer water temperatures. (There is some evidence that suggests that raising the temperature to the maximum the fish will tolerate can be very effective at eliminating white spot.)

Infected fish may “flash”, i.e., rub against the tank bottom, or objects in the tank in an attempt to scratch off the parasite. The classic sign of an "Ich" infection is the presence of small white spots on the skin or gills. These lesions look like grains of salt on the skin or fins of the fish. Prior to the appearance of white spots, fish may show signs of irritation, flashing, weakness, loss of appetite, and decreased activity. Any behavioural changed may be an indication of an infection by white spot. Fish should be inspected using a torch as the early stages of the infection are not easy to see in dim lighting. If the parasite is only present on the gills, white spots will not be seen at all, but fish will die in large numbers. In these fish, gills will be pale and very swollen. White spots should not be used as the only means of diagnosis because other diseases may have a similar appearance. Gill and skin scrapings should be taken when the first signs of illness are observed. If the "Ich" organism is seen, fish should be medicated immediately because fish which are severely infected may not survive treatment. An outbreak of white spot is an emergency situation which requires immediate treatment: if left untreated, this disease may result in 100% mortality. Treatment may take up to three weeks.

Treatment: Control of "Ich" outbreaks can be difficult because of the parasites' unusual life cycle and the effect of water temperature on its life cycle. Only the free-swimming tomites are susceptible to chemical treatment. This means that application of a single treatment will kill tomites which have emerged from cysts and have not yet burrowed into the skin of host fish. This single treatment will not affect organisms which emerge after the chemical has broken down or been flushed from the system. Repeated treatments, however, will continually kill the juvenile tomites, preventing continuation of the infection. The epizootic will be controlled as more adult parasites drop off the sick fish, encyst, and produce young which cannot survive because of the repeated application of chemicals. This process will be greatly accelerated if organic debris can be removed from the tank or pond following treatment. This will remove many cysts from the environment, decreasing the number of emergent tomites.

Water temperature has a tremendous influence on how fast the life cycle for "Ich" is completed. At warm temperatures (75-79°F), the life cycle is completed in about 48 hours. At cooler temperatures the life cycle is prolonged, for example, at a water temperature of 60°F, the life cycle may be 4 or 5 days.

Treatments should never be discontinued until all signs of "Ich" has stopped. Fish should be closely watched during recovery; the weakened fish may be susceptible to a secondary bacterial infection. The choice of chemical used to treat "Ich" will be based upon, species of fish to be treated, and the type of system fish are housed in. In general, copper sulfate, formalin, and potassium permanganate* are all effective against "Ich" when applied at the correct concentration in a repetitive manner. NOTE: Formalin can produce a false positive ammonia reading by most ammonia test kits, including Nesslers reagent.

Special Considerations for Treatment of Food Fish Species. Always check if chemicals are approved for use on food fish in your jurisdiction.

For ponds, the treatment of choice for "Ich" is copper sulphate. The chemical is effective and relatively inexpensive, an important consideration when large volumes of water are treated. The disadvantage of copper sulphate is that it is extremely toxic, particularly in water of low alkalinity. NEVER use copper sulphate without testing the total alkalinity of the water, carefully measuring the dimensions of the pond to be treated, and weighing the amount of chemical to be applied.

The concentration of copper sulphate to apply is often calculated by determining the total alkalinity of the water and dividing that number by 100. For example, if the total alkalinity of the pond is 100 mg/L, then 100/100 = 1 mg/L copper sulphate. Do not use copper sulphate if the total alkalinity is less than 50 mg/L. Use of copper sulphate may lead to severe oxygen depletions, therefore, emergency aeration should always be available. Use of copper sulphate during hot weather, or when algae blooms are dense, is strongly discouraged. Remember, if you do not know the alkalinity of your water and can not measure it then DO NOT USE COPPER SULPHATE.

If you are unable to use copper sulphate in pond because of low alkalinity, lack of aeration, or you are not comfortable using it, potassium permanganate* can be used instead. The primary disadvantage of potassium permanganate is its high cost. However, it is equally effective and safer to use than copper sulphate. Potassium permanganate can be applied at a concentration of 2 mg/L which will result in a purple-pink colour of the water. If the water turns yellow or brown in less than 8 to 10 hours, then the treatment should be repeated. Usually, a maximum of three applications (2 mg/L each) is recommended during any one treatment (maximum concentration of 6 mg/L).

If fish are maintained indoors in a tank system, formalin can be used to treat "Ich". Formalin is not the ideal treatment for ponds, but works nicely in tanks with vigorous aeration. Formalin should not be run through a biofilter, however, as it will kill the bacteria in the filter and ammonia levels may increase to lethal levels. A short-term bath of 250 mg/L for 30 to 60 minutes can be followed by a water change. Cleaning the tank will also decrease the number of parasites. When applying a concentrated treatment such as formalin, NEVER leave the fish in the treated water longer than recommended, and NEVER leave them unattended. Sick fish may be unable to tolerate a full treatment. If they appear stressed or try to jump out of the tank, flush the chemical from the system immediately. A long term bath of formalin can be used in a tank system at a concentration of 15 mg/L and does not need to be flushed out. NOTE: Formalin can produce a false positive ammonia reading by most ammonia test kits, including Nesslers reagent.

Salt can also be used to control "Ich" infections in small volumes of water. This is not practical in ponds because even a light salt solution of  1 gram per litre., would require large quantities of salt. In small volumes (i.e. glass aquariums or aquaculture tanks), however, salt can be useful. Fish can be dipped in a 30 grams per litre solution for thirty seconds to several minutes, or they can be treated in a prolonged bath at a lower concentration (3 gms per litre). Salt at low concentrations (half to 1 grams per litre solution) is an excellent means of controlling "Ich" in recirculating systems without harming the biofilter. NOTE: Salt is an extreamly usefull tool to manage disease and other stresses on fish. You should make yourself aware of the salt tolerances of the species you are dealing with. More information on salt can be found here.

Special Considerations for Treatment of Ornamental Fish. Always check if chemicals are approved for use on aquarium fish in your jurisdiction.

Fish which are not intended for human consumption can also be treated with the chemicals described above for food fish. Copper sulphate or potassium permanganate* work well in ponds, whereas formalin or salt may be easier to use in smaller volumes of water.

Malachite green is another chemical which can be used to treat ornamental fish that are housed indoors. This chemical should NEVER be used to treat food fish. The chemical is hazardous to handle- it is known to cause cancer, mutations, and is harmful to foetuses. Gloves and a protective mask should always be worn when handling the concentrated powder. Pregnant personnel should NEVER handle this chemical.

It is commonly used to control parasitic protozoans on ornamental fish and is quite effective when used at concentrations of 0.05 to 0.10 mg/L as an indefinite bath. This chemical is extremely harsh on fish, particularly on gill tissue, so be careful not to overdose the fish.

Malachite green can also be combined with formalin (0.2 mg/L malachite green mixed with 25 mg/L formalin) to treat external protozoan diseases. The two chemicals work well together and are quite effective. Malachite green can be very toxic to scaleless fish and should be avoided on these species.

WARNING: Malachite green is illegal in many jurisdictions. Check first !


Trichodinia sp:  There are three genera which form the Trichodina complex: Trichodina, Trichodonella and Tripartiella, however, all three are commonly referred to as “Trichodina”.  All are approximately 100 mm in diameter and have a saucer to “frisbee” shape and are ringed with cilia around its entire surface.  They have a circular arrangement of tooth-like structures (denticular ring) within the body which provides them a characteristic appearance in fresh gill and skin cytology preparations.  Fish with severe gill infections of trichodina will have respiratory and osmoregulatory difficulty and may gasp at the surface as well as “flash.  Fin erosions and/or ulcerations can be observed in serious infections.  Diagnosis of this parasitic disease is dependent upon identification of the parasite within the skin or gill cytologic preparations or histopathology.

  Treatment options:                                                                             

1. Copper sulphate, prolonged bath, total alkalinity/100 (up to 2.5 mg/L), Do not use if total alkalinity < 50mg/L.

2. Short term Potassium permanganate* bath of 10 mg/L, for 30 min, or a long term bath of 2 mg/L*

3.  Formalin short term bath, 150--250 mg/L, 30 min, or long term 15--25 mg/L. NOTE: Formalin can produce a false positive ammonia reading by most ammonia test kits, including Nesslers      reagent.

4. Long term salt bath of  about 3 grams per litre.

Anchor "worm" Lernaea  Adult female Lernaea look like a piece of heavy nylon fishing line, about 1 cm long, protruding from the skin, sometimes with two egg sacs visible on the end. A bit like a tiny palm tree with only two fronds.

Treatment: Strike, is the best chemical to use. It is simply added to the tanks or ponds at the dose rate on the label and allowed to dissipate. New fish should be quarantined for at least three weeks at 25 degrees Celsius and watched for emergence of the adults. 

Costia sp: This parasite is also known as Ichthyobodo sp  .  These are obligate flagellate parasites with a direct life cycle.  The free-swimming form is renniform, and approximately 10-20 mm long with two pairs of flagellae; whereas the attached form is pear-shaped and attaches to the gills and skin.  Disease associated with this parasite includes increased cutaneous mucous production (hence the lay terminology of “blue slime disease”), epithelial hyperplasia of the skin and gills, ulceration and erosion of fins. Treatment with about 3 grams per litre of salt, long term bath.


Argulus, or fish lice, is a two to four millimetre flat louse-like crustacean, which scurries over the skin and into hiding when fish are handled for examination. Treatment: Two treatments with Strike, a fortnight apart, will remove most or all Argulus. New fish should be quarantined for at least two weeks before introduction.

Chilodonella spThis is a motile ciliated protozoal parasite which causes disease in the skin and gills of fish.  It is typically heart-shaped with the posterior end being broader and slightly notched.  It measures approximately 20-40 mm in width and 30-70 mm in length and its surface is covered with cilia.   There is a large macronucleus in the posterior portion of this organism and a smaller micronucleus is near or within the macronucleus.   This parasite has been attributed to death of fish due to respiratory and osmoregulatory imbalances associated with severe gill parasitism. 

Treatment: In tanks use about 2 grams per litre of salt solution as a long term bath.


Henneguya sp:  These parasites were once thought to be responsible for the gill disease  in catfish in the USA, but are now thought to be less pathogenic, although they can cause respiratory problems if present in large numbers.  They have a very characteristic paired, long, whip-like tail giving them a spermatozoan-like appearance.  Size of spores range from 8-24 mm in length.  The cysts can be found in the gill filaments using a microscope.

Treatment: The parasite requires an aquatic worm to complete its life cycle. To break the life cycle keep the fish in tanks for two weeks with a formalin concentration of 15--25 mg/L with salt at about 2 grams per litre. This will help keep worm hosts away while the parasite life cycle is in progress.


Camillanus is easily recognized as a small thread-like worm protruding from the anus of the fish. Usually, a number of worms can be seen protruding from the fish’ anus. Sometimes there is a small bump just above the anus. Fish can sometimes appear skinny if infection has been prolonged.

Treatment: Pitiperazine Sulphate mixed in food at 10mg per kg of food and fed at the rate of 1% of body weight per kg of fish. This should be fed to fish for 3 days.

Cestode-like helminth, is a type of worm commonly found in the gut of Jade Perch. It can be found in the stomach and the lumen (small pouches) of the stomach, also in the intestine of the fish. All batches of jade perch fingerlings/frey should be treated prior to shipping.

Treatment: Praziquantel at 50mg/kg fish weight added to feed and fed for three days. May also be effective at 10 mg/L  of tank water.

Metacecarial trematode is a worm found on in the mussel tissue, head, eye, jaw tip, and heart. The inflammatory response in the encysted tissue include, formation of a blood blister around the cyst with eventual deposition of melanin by melanomacrophaces giving a blackening appearance in the fixed tissue. Fibrous encapsulation surround the immediate area of the metacercaria. Eye based may produce pop eye. This worm can infect humans if uncooked fish are consumed. This worm can be controlled by keeping freshwater snails out of plankton ponds.

Treatment: Praziquantel at 330mg/kg mixed in feed and fed for 7 days. Fish may be sensitive to Praziquantel at this dose level.

* Potassium permanganate, KMnO 4 , is a chemical oxidizing agent that will react with any organic matter in a pond including algae, bacteria, fish, particulate and dissolved organic, and organic bottom     sediments. It has been used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial and fungal infections. Contrary to some reports, potassium permanganate does not add     significant amounts of oxygen to water and can actually decrease dissolved oxygen concentrations by killing algae that produce much of the oxygen in ponds. Always momotor oxygen when using any chemicals in ponds or tanks.

Precautions When Using Potassium Permanganate 

A few helpful reminders and precautions before using potassium permanganate include: 
• Be sure you have a problem that warrants treatment. Potassium permanganate is expensive. Have your fish properly diagnosed and carefully consider the cost. 
• Potassium permanganate is a strong oxidizer and can burn skin, eyes, and other body parts. It will stain you and everything it touches brown. Always use safety protective gear including rubber gloves,     goggles and old clothes. A   dust mask is advisable to prevent irritation to your respiratory tract. 
• Be sure to estimate water volume accurately, and disperse the chemical evenly over the entire pond to prevent hot spots, areas of the pond with excessive amounts of chemical. 
• Potassium permanganate   can kill algae. Low oxygen conditions can occur following treatment. Be prepared to aerate after treatment. 
• Frequent treatment can harm fish. Wait at least four days before repeating treatment. If fish do not respond to treatment, reevaluate them to confirm the diagnosis.   



Ozone-disinfection systems introduce ozone, O3, a highly reactive molecule, into a contact chamber (isolated from the main system holding the fish). Ozone generators are more complex than UV-sterilizing units, and they require the presence of a high energy field through which dry filtered air or pure oxygen flows. The ozone oxidizes (i.e., reacts with and breaks down) dissolved and suspended molecules, as well as molecules within and on pathogens in the water. In freshwater systems, ozone rapidly breaks down or dissipates once it makes contact with the water; therefore, water from a contact chamber can be reintroduced into the system quickly, if the system is designed properly. However, as ozone is so highly reactive, all ozone must be eliminated from the water prior to its reintroduction. This elimination can be accomplished in several ways including degassing.

Ozone does not appreciably oxidize ammonia (i.e., convert ammonia into nitrite). In recirculating systems, this reaction is commonly accomplished by nitrifying bacteria in the biofilter. Ozone does oxidize nitrite to nitrate, so it augments the efforts of nitrifying bacteria in the biofilter. If the ozone is turned off in a system adapted to its presence, the nitrifying bacteria in the biofilter may not be present in high enough numbers to prevent nitrite levels from temporarily spiking in the system.

In addition to sterilizing water, ozone helps other parts of the system. Ozone promotes water clarity by rapidly breaking down dissolved and particulate organics that discolor or cloud the water. Ozone improves biofiltration efficiency by decreasing the organic load in the biofilter. This organic load is a food source for bacteria known as heterotrophs. Heterotrophs include many disease-causing bacteria that often compete with nitrifying bacteria for space and oxygen in the biofilter.

Ozone is more dangerous than UV sterilization. Small amounts in the water can kill fish and residual amounts in the air can be toxic to humans. by-products of ozonation can increase the risk of disease in fish. For example, chemical by-products of ozonation have been suggested as one potential cause of head and lateral line erosion, although, research to demonstrate this association has not be completed. Also, some species are much more sensitive to residual ozone levels than others.



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