Chemical Treatments
A number of products are manufactured and marketed for the therapy and prophylaxis of fish diseases. Some of these chemicals can be dangerous if applied incorrectly and should only be used by experienced aquarium specialists. A very thin line separates effective treatment levels from overdoses that will kill the fish.
ACRIFLAVINE - this dye has both antibacterial and antiprotozoal activity at a dose of 2 to 3 ppm. It will also kill aquatic plants, colour the water yellow. Many organisms are resistant and it has been largely replaced by more specific treatments. 5-10 mg/L in water for several hours to several days.
ACRIFLAVINE NEUTRAL -- 5–10 mg/L in water for several hours to several days.
ALKA-SELTZER -- several tablets in 17 to 34 ounces of water for euthanasia of fish by CO2 toxicity.
ALUM (ALUMINIUM SULPHATE) -- dose “to effect” to decrease pH in pools and aquariums.
ACETIC ACID -- 1000 to 2000 ppm dip for 1 to 10 minutes as a parasiticide for fish.
BENZALKONIUM CHLORIDE -- this blend of quaternary ammonium compounds is used at a concentration of 1 mg/L as a one-hour bath to treat susceptible bacterial diseases, especially gill conditions where excess mucus production is a problem; it is also utilised as a disinfectant for nets and other equipment.
BENZOCAINE -- used for sedation of fish at a dose of approx. 10 to 40 mg/L of aquarium water; for anaesthesia at a dose of approx 50 to 500 mg/L in the water or sprayed as an aerosol on the gills; and for euthanasia “to effect”.
CALCIUM CHLORIDE -- used to increase water calcium concentration to insure proper egg hardening. Dosages used would be those necessary to raise calcium concentration to 10 to 20 ppm.
CALCIUM CARBONATE (CaCO3) -- up to 150 ppm indefinitely to increase the hardness of water for holding and transporting fish in order to enable fish to maintain osmotic balance.
CALCIUM OXIDE -- used as an external protozoacide for fingerlings to adult fish at a concentration of 2000 mg/L for 5 seconds.
CARBON DIOXIDE GAS -- for anaesthetic purposes in fish.
CHARCOAL (ACTIVATED CARBON) -- used in filtering systems to eliminate chlorine, as well as antibiotics and other impurities. Charcoal is sold by many aquarium supply companies in bags which fit inside individual filters, or as blocks which are inserted into the lines of multi-tank filtering systems (200 mg/L).
CHLORAMINE-T -- at a dose of 0.5 to 2 mg/L, this disinfectant has been reported as a successful treatment for a variety of bacterial infections of aquarium fish; its action is based on the fact that it slowly breaks down to hypochlorous acid, releasing oxygen and chlorine. Chloramine-T can be administered in a bath at the following dose rates for 2–3 days, using lower dose rates in soft water with a low pH:
pH Soft Water Hard Water 6.0 2.5 ppm 7.0 ppm 6.5 5 ppm 10 ppm 7.0 10 ppm 15 ppm 7.5 18 ppm 18 ppm 8.0 20 ppm 20 ppm
This chemical is best used by aquarium hobbyists simply as a disinfectant for equipment.
CHLORAMPHENICOL -- Columnaris, Enteric Red Mouth, Finrot, Furunculosis, Haemorrhagic Septicaemia, Pasteurellosis, Ulcer Disease, Vibriosis. (a) 50-70 mg/kg of food/day for 5-10 days (b) 10-50 mg/L of water, as a bath
This drug should not be used for home aquaria because it is unstable in water, and poorly absorbed by target fish; and, it can cause fatal human aplastic anaemia if touched by a person who is allergic to the compound.
CHLORMON -- used to neutralizes ammonia, chlorine and chloramines. Chlormon deals with ammonia instantly, destroying it completely leaving the tap water safe for immediate use. Chlormon used in fish transport water, eliminates ammonia as it is produced during transit, allowing for a longer and safer journey. May be added directly to a bag of fish. Chlormon is also safe for invertebrates, no effect on marine salts. Quantitative dose rate 5 mL of Chlormon per 20L neutralizes 0.75 ppm ammonia. 5 mL/20L also neutralises chlorine and chloramines in tap water.
CHLORINE -- use household bleach equal to 5.25% sodium hypochlorite as a disinfectant for aquarium equipment; chlorine can then be rinsed off with sodium thiosulfate wash.
CHLOROQUINE DIPHOSPHATE -- this anti-malaria drug is effective against Amyloodinium at a dose of 40 mg/gal used as a prolonged immersion of three weeks’ duration.
COPPER SULPHATE (CuSO4) -- this “old-time” medication has seen decades of use both as an effective algaecide and an external parasite treatment, but there are much better preparations available today. Copper sulphate has also been used with success as an algae control by aquarium owners at the 0.1 to 0.2 ppm level, but some find the resulting water chemistry too harsh to grow decorative plants and are forced to remove it through charcoal filtration. Copper sulphate is extremely toxic, particularly in water of low alkalinity. Never use copper sulphate without testing the alkalinity of the water, carefully measuring the volume of the aquarium or 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 aquarium 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. If you are unsure how to measure the alkalinity of your water, or have never used copper sulphate, then do not use it.
Because of its algicidal activity, copper sulphate can cause dangerous oxygen depletions, particularly in warm weather. Emergency aeration should always be available when copper sulphate is applied to your aquarium systems. Copper sulphate should not be run through the biofilter on a recirculation system, as it will kill the nitrifying bacteria. If possible, tanks should be taken “off-line” during treatment with copper sulphate. If necessary, clean the biofilter manually to decrease organic debris and residual parasite load.
When using a commercially formulated copper cure, always follow the label instructions for dosage rates. Chelated copper will stay in solution longer than copper sulphate and appears to be safer to fish. You can create your own chelated copper by using two parts citric acid to one part copper sulphate, by weight. Combine both in distilled water and dissolve them together. It is important to remember that you will be treating with the copper sulphate and not the citric acid, so when weighing the formula, use only the weight of your copper sulphate in calculating dosages.
Most fish are extremely sensitive to copper. Concentrations of copper as low as 42 and 17 µg Cu/L were found to be acutely toxic to the Penny-fish (Denariusa bandata) and the Eel-tailed Catfish (Porochilus rendahli) respectively. Melanotaenia s. inornata and Ambassis spp. have been found to be sensitive to copper; half of the individuals tested died at copper concentrations between 120 and 200 µg Cu/L. The atyid shrimp, Caridina sp. is extremely sensitive to copper, dying at levels of only 2 µg /L. River prawns, Macrobrachium sp. were found sensitive to copper with half the individuals dying at 160 µg Cu/L. Snails are also known to be very sensitive to copper. For example the snail Physatra gibbosa (of New South Wales), succumbs at 31 µg Cu/L after 7 to 9 days.
Copper sulphate is for specialist use only as it is highly toxic and requires removal. It is inadvisable to use this compound where other treatments are available.
DICHLORVOS -- (see Organophosphates)
DIFLUROBENZURON -- used to treat crustacean copepods as a prolonged immersion at a dose of 0.11 mg/gal.
DOXYCYCLINE and MINOCYCLINE -- used against susceptible bacteria as a prolonged immersion at a dose of 2 to 3 mg/L. EPSOM SALTS -- (see Magnesium Sulphate)
FENBENDAZOLE -- used to control intestinal helminths in fish. A dosage of 25 mg/kg, delivered in food for 3-5 days, has been commonly recommended, but this regimen has not been evaluated in controlled trials. Also been reported as an effective control for hydra used at 2 mg/L. This chemical is available in various formulations and trade names.
FLUMEQUINE -- used for infections caused by susceptible bacteria; most effective as a dip if the water pH is near neutral; as a dip, use 50 to 100 mg/L for three hours.
FMC -- is a mixture of malachite green, methylene blue and formalin and is used to control external fungal infections in fish eggs and ornamental fish breeding (Bassleer, 1983). The ingredients malachite green and formalin are mostly therapeutic agents against fungi and protozoans, and methylene blue, another organic dye, acts as an antidote and oxygen donor. The treatment success as well as the toxicity of the chemicals is determined by the toxicity of each of the substances and synergistic effects among them.
FMC consists of the following combined ingredients:
Formalin (37%) = 1 litre [or 100 ml] Malachite green (oxalate) = 3.7 gm [or 0.37 gm] Methylene blue = 3.7 gm [or 0.37 gm]
Dosage: 1.0 to 1.2 ml/100 litres water (25 drops/100 L). Change the water (50%) after one day treatment and add another dose.
NB: This medication can be more toxic in soft acid water, and also at higher temperatures.
FORMALIN -- used as a water treatment to control external parasitic infections. It is extremely effective against most protozoans, as well as some of the larger parasites such as monogenetic trematodes. Formalin effectively kills parasites on the gills, skin, and fins. It is not generally considered the preferred treatment for external bacterial or fungal infections. Formalin can be used in a short-term bath at a concentration of 175–250 mg/L if water temperature is greater than 20° Celsius for no more than 30–60 minutes. Treatment should never exceed 1 hour even if the fish show no signs of stress. It can be used as an indefinite bath at a concentration of 15–25 mg/L for up to 12 hours.
Formalin has a high level of toxicity and fish under treatment must be followed closely for toxic signs such as respiratory difficulties. Under some conditions, fish may be stressed by normal treatment concentrations. Heavily parasitised or diseased fish often have a greatly reduced tolerance to formalin. Such fish do not tolerate the normal tank treatment regime the first time they are treated, and the time or dosage or both may need to be reduced. If adverse reaction is observed, fish should be removed from the treatment tank at once and placed in clean well-aerated water. Careful observations should always be made throughout the treatment period whenever tank treatments are made.
Formalin is a generic term, which describes a solution of 37–50% formaldehyde gas dissolved in water. Formaldehyde is a colourless gas with a pungent, suffocating odour at room temperature; the odour threshold for formaldehyde is 0.83 ppm. The chemical formula for formaldehyde is CH2O and the molecular weight is 30.03 g/mol. Solutions of formalin for use as a fish medication should contain 10–15% methanol, which inhibits formation of paraformaldehyde, a highly toxic substance.
Formalin can be combined with malachite green (0.1 mg/L malachite green mixed with 25 mg/L formalin) to treat external protozoans diseases. The two chemicals work well together and are very effective for the control of various external parasites of freshwater fishes.
The toxicity of formalin and therapeutical success is influenced by water parameters and is falling out of favour as an aquarium treatment because of its undesirable qualities. It is a reducing agent and thus lowers the available oxygen level in the water, which is hardly favourable to fish being treated. Each 5 mg/L of formalin applied removes 1 mg/L of dissolved oxygen. However, this can be avoided in aquarium systems by always supplying adequate aeration whenever formalin is used.
Formalin toxicity is increased at high water temperatures. If water exceeds 21° Celsius, the concentration of formalin delivered in a prolonged bath should be decreased. Formalin is carcinogenic to laboratory rodents and causes contact dermatitis and lung damage in people; it is volatile; and, it is a direct irritant to fish gills. Laboratory experiments have shown that juvenile fish exposed to high concentrations died and fish embryos exposed to low concentrations were unable to hatch.
Formalin is for specialist use only. It is inadvisable to use this compound where other treatments are available.
FULLER'S EARTH -- used to reduce the adhesiveness of fish eggs to improve hatchability.
FURALTADONE -- related to nifurpirinol with which it shares antimicrobial activity; as an immersion, use 20 to 50 mg/L and treat fish for one day.
FURAZOLIDONE -- related to nifurpirinol with which it shares antimicrobial activity; as a prolonged immersion, use 1 to 10 mg/L and treat for 24 hours.
HYDROGEN PEROXIDE -- use as a treatment of acute oxygen insufficiency at a dose of 0.25 ml of a 3% H2O2 solution per litre of water. It can also be used to treat external protozoans at a dose of 10 ml of a 3% solution per litre of water as a 10 to 15 min bath. Used at 250–500 mg/l to control fungi on all species and life stages of fish, including eggs.
There are many different doses suggested in the literature for use in aquarium fish. However, because there are hundreds of species of ornamental fish, certain factors must be taken into account when using Hydrogen peroxide. It can be very toxic to some species, and certain life stages may be more sensitive. Increasing temperature seems to increase the potential toxicity. Dosage and duration of treatment will also determine whether fish being treated will live or die. Hydrogen peroxide can cause mortalities primarily by damaging the gills. Therefore, toxic effects will often be seen related to gill damage, as indicated by gasping near the surface, or increased ventilation rates.
Contrary to popular belief, in water with relatively low organic content, the concentration of Hydrogen peroxide does not decrease significantly. Of course, any increase in organic loading will change this factor, but the bottom line is that Hydrogen peroxide does not break down as quickly as some may think. Water changes are required after treatment.
More work has to be conducted on the use of hydrogen peroxide, especially its safety, efficacy, and effects on biofiltration. More organics in the system lessen the likelihood that biofilter bacteria will be damaged or killed by these chemicals. However, too high an organic load will render this chemical ineffective as a treatment.
IVERMECTIN (1%) -- Some studies have shown that Ivermectin added directly to aquarium water has been useful in treating Camallanus worms in fish. The dose used was 0.7 millilitres of a 1% injectable solution per 76 litres of water. The dose was added over a period of four days (0.1, 0.2, 0.2, and 0.2 millilitres). A solution of 1 part Ivermectin 1% in 19 parts distilled water can be made and administered as a split dose of 2 ml on day one, 3 ml on day two, and 3 ml on day three followed by a water change on day four. However, because this drug has a narrow margin of safety, some veterinarians advise against any use of Ivermectin for aquarium fishes because it can cause neurologic signs and death in fish at therapeutic doses.
LEVAMISOLE HCL -- used for the treatment of susceptible nematodes at a dose of 10 mg/L of water as an immersion. 1 mg/L 1 to 2 days for skin and gill flukes; 2 mg/L once per week for 3 weeks for Camallanus.
MAGNESIUM SULPHATE -- used to treat external monogenetic trematode infestations and external crustacean infestations in fish at all life stages. Used in all freshwater species. Fish are immersed in 30,000 mg/L MgSO4 and 7000 mg/L NaCl solutions for 5 to 10 minutes.
MALACHITE GREEN -- Malachite green is a triphenylmethane dye originally developed in the 1920s as a textile dye used to colour materials such as fibres, silk, leather, and paper products. Malachite green has also been extensively used in aquaculture throughout the world since 1936 as topical antiseptic or to treat parasites, fungal and bacterial infections in fish and fish eggs. It has been largely used to prevent outgrowth of oomycete fungi on fish and fish eggs, both as a post-infection therapy and prophylaxis. It was found to be the most effective fungicide among 49 compounds tested against an oomycete fungus.
Aphanomyces invadans and Aspergillus flavus infections have also been treated effectively with malachite green. Malachite green was found to be highly active against mycoses caused by the fungus Saprolegnia infecting fish and fish eggs in commercial aquaculture. Fish egg treatments at concentrations of 5–10 mg/L were mainly recommended applied for 5–30 minutes, once or twice daily, or twice weekly. In aquarium and ornamental fish rearing, dips, shortterm baths and long-term baths are used. Dosage ranges from 100 ppm used for a few seconds as a dip application down to 0.15 ppm used in prolonged treatments of aquarium fishes.
Several studies have reported that malachite green applied to water is rapidly taken up by the fish and distributed into all organs. The toxicity as well as successful use of chemicals frequently depends on dosage, abiotic parameters (e.g., temperature, hardness, organic load, pH, and others. Also the species and the developmental stages of the fish. In an effort to reduce concentrations of, and exposure periods to, malachite green, mono-component malachite green baths were gradually replaced with multi-component baths. A combined malachite green and formaldehyde bath [0.25 mg malachite green and 0.125 ml 36-38% aqueous solution of formaldehyde (formalin) dissolved in 1 litre of water] appeared very effective. The duration of the bath was 2–6 hours in holding tanks. When treating fish with ichthyophthiriosis it was recommended to repeat the baths 2 or 3 times a week.
In the aquacultural industry, technical grade malachite green was used in the past. Its exact chemical composition was not often given. When using it, it was therefore necessary to take into account its different toxicological and therapeutic properties. The malachite green bath treatment without a prior test of fish tolerance could result in the death of all the stock thus treated. For that reason, each new production batch of malachite green had to be tested for toxicity to fish and for its antiparasitic action. However, improved production practices made it more suitable as a fish therapeutant.
In the 1960s, malachite green proved to provide the most effective treatment against protozoan ectoparasites, particularly Ichthyophthirius multifiliis. It became even more important when its effectiveness against Saprolegnia in fish eggs were demonstrated. Since then, malachite green has been extensively used in controlling infections due to bacteria, fungi, protozoans and monogenetic trematodes on eggs, fry and adult fish. It is used by itself, or in combination with formalin, salt or dimethyl sulphoxide (DMSO). Malachite green is also used in multi-component treatment baths (malachite green in combination with formalin, brilliant green, crystal violet, methylene blue, etc.).
Malachite green combined with formalin (0.1 mg/L malachite green mixed with 25 mg/L formalin) work well together and are very effective for the control of various external parasites of freshwater fishes. One of the most favourite preparations of aquarists was a mixture of formalin, malachite green and methylene blue known as FMC (3.5 grams malachite green and 3.5 grams methylene blue in 1000 ml formalin). Curative baths were prepared by adding 1.5–3 ml FMC to 100 litres water (Bassleer, 1983). The overall procedure took three days, and every day a new curative bath was prepared. For preventive baths of ornamental and aquarium fish eggs, malachite green was mainly used in the FMC formulation.
In recent years, however, there have been strong moves against malachite green application, especially with respect to its use in food fish. Scientific evidence indicated that malachite green and especially its reduced form, leucomalachite green, might persist in edible fish tissues for extended periods of time. In 2000, the use of malachite green for food fish was banned in the EU because the general public may become exposed to malachite green through the consumption of treated fish. This is because the chemical is believed to have potential teratogenic, mutagenic or carcinogenic attributes. While there has been no evidence actually linking malachite green with any carcinoma, its use in food fish has been banned in many countries. Studies have also indicated that malachite green may have very long withdrawal times. Residues of malachite green have been found in fry some 30 days after eggs were disinfected. At present, malachite green can be used only in aquarium and ornamental fish breeding.
Despite its toxicity, it is commonly used to control parasitic protozoans on ornamental fish. Malachite green is used for treatment against parasitic protozoans infecting the skin of freshwater aquarium fishes. When used as directed, the medication will control or prevent the following common protozoan parasites: Ichthyophthirius, Ichthyobodo, Chilodonella, Ambiphyra, Cryptocaryon, Epistylis, Piscinoodinium and Trichodina. Malachite green is also effective against common external fungal infections of fishes and eggs, which include Achlya and Saprolegnia. A short-term malachite green bath is also recommended as a treatment of gill flavobacteriosis. It has also been used to control skin and gill flukes. An extensive body of literature supports its use as an effective agent in the control of the above mentioned pathogens.
Malachite green is quite effective when used at concentrations of 0.05 to 0.10 mg/L as an indefinite bath or 1–3 mg/L of water for up to 60 minutes. It is also used to treat eggs against fungal infections as a 2 mg/L wash for 30 to 60 minutes. However, this chemical can be extremely harsh on fish, particularly on gill tissue, so be careful not to overdose the fish. Lethal concentrations for fish and recommended therapeutic concentrations are sometimes very close to each other. Dosage calculations should be doublechecked before applying treatment. Therapeutic concentrations could be different for distinct species as well as for different developmental stages of fish. It is usually applied at 0.01 ppm for postlarvae and 0.1 ppm for juveniles. It also seems to be more toxic to scaleless fish than fish with scales when used at the same concentration, and should be avoided on these species.
The progress of intoxication is very rapid. Typical clinical symptoms include restlessness and uncoordinated movements of the fish in the tank. The fish move in the upper half of the tank, leap above the water surface, and gasp for air, which is followed by the loss of balance, apathy and death. The pathological anatomical picture of fish intoxication with malachite green is characterised by greenish tinge of their skin and increased production of skin slime. The gills are oedematous, with excessive amounts of mucous matter, and are discoloured by the agent. Vessels in the body cavity were dilated, and muscle tissues and internal organs were often light-green in colour. In addition to its high acute toxicity, malachite green may be the cause of a number of side-effects on the fish treated. Malachite green bath treatment of fish eggs may delay fry hatching and increase the frequency of abnormalities (malformation of the head and jaws, spine deformation or missing fins).
Large differences in the toxicity of malachite green in dependence on its purity and varying concentrations of residual impurities that could render more or less toxic are another major obstacle in its application. High-quality grades of malachite green can be produced by the inclusion of additional purification stages in production, but even a nominal 100% malachite green dry powder by analysis can only contain 82% (oxalate) or 95% (hydrochloride), the rest of the weight being the acid component. Different toxicological properties of malachite green were confirmed in a series of acute toxicity tests on common carp and rainbow trout in which 10 types of malachite green obtained from different sources were investigated. It follows from these experiments that lethal concentrations of some types of malachite green are very close to therapeutic concentrations. In one case the recommended therapeutic concentration of malachite green was even higher than its lethal concentration.
When treating fishes, it should be borne in mind that malachite green toxicity is significantly influenced by the quality of used water. The toxicity and hence of course its effectiveness are primarily influenced by the reducing substances present in water, for example organic substances, calcium-ions, pH and temperature values. The toxicity of malachite green is reduced for example by humic substances in soft water. At lower water temperatures, the fish can tolerate slightly higher concentrations of malachite green than at higher temperatures. During the hot summer months the exposure time for malachite green treatment should be decreased. Malachite green is also more toxic at low pH. Malachite green has two forms depending on pH. The initial strong green coloured prevails at low pH (acidic), while in alkaline water it is converted to a colourless carbinol form. So in alkaline water it may seem that it has disappeared, but it is still present, but invisible!
For the above reasons, it is important to pay great attention to the selection of malachite green to be used, take water parameters and temperature into account and also observe recommended dosages and exposure periods. One should follow the manufacturer’s instructions for treatment, as different manufacturers use different concentrations of the active ingredients.
Malachite green has gradually been replaced in the treatment of superficial fungal infections and infections with protozoan parasites with the exception of Ichthyophthirius multifiliis. In treatments of topical mycoses, malachite green is being replaced mainly by formaldehyde, potassium permanganate and bronopol baths. Sodium chloride and chloramine have been successfully used in the treatment of protozoan infections and flavobacteriosis of the gills respectively.
MEBENDAZOLE -- Mebendazole is chemically related to flubendazole and fenbendazole. It is a benzimidazole derivative, and is a useful broad spectrum anthelmintic, the drug of choice for mixed worm infestations. ~ used to treat monogenean flukes; as a 24 hour immersion use 1 mg/L.
METHYLENE BLUE -- used against ciliates infecting the skin at 1 to 3 mg/L in a bath for 3 days, or 30 mg/L for a short duration bath. Methylene blue may be used for the treatment of Ichthyophthiriasis (white spot disease), skin and gill flukes, velvet disease, Costiasis, Chilodonelliasis, Trichodina and as a palliative medicine in all cases of disease of the gills, where fishes suffer from difficulty in breathing.
Methylene blue is a redox dye which raises the oxygen consumption of cells. This means that the hydrogen to be oxidised is passed on to the oxygen. Each molecule of the dye is oxidised and reduced about 100 times per seconds. Thus, while disinfection results from this, methylene blue is also excellent against methemoglobin intoxication. The therapeutic action of methylene blue on bacteria and other parasites is probably due to its binding effect with cytoplasmic structures within the cell and also its interference with oxidationreduction processes.
Methylene blue is also effective against superficial fungal infections of fishes and may be used as an alternative to malachite green for the control of fungus when it is known that the fish to be treated are sensitive. It is safe for use with fish eggs and fry for the prevention of fungal infection. It is particularly effective against Saprolegnia by applying 3 mg/L for long duration. At a concentration of 2–3 mg/L, it can be used as an indefinite bath for fish at all ages. When used against gill rot and other bacterial disease, the rate is at 8–10 mg/L as a bath treatment. It can also be applied during quarantine treatment of aquarium fishes by using an indefinite bath of 1 mg/L.
Methylene blue has a wide safety margin and is non-toxic when used as recommended. Fish tolerate relatively high dosages without side effects. However, it should not be used in recirculation systems that utilise biological filtration, as it will interfere with the normal biological processes of nitrifying bacteria. It can also interfere with normal plant growth. Methylene blue is best used in bare aquariums as porous materials such as rock and driftwood will absorb the dye and it may permanently discolour the silicone sealant. At the conclusion of treatment, a partial or complete water change should be made to remove any chemical residues or use activated carbon in the filter.
Methylene blue comes in various fish medication preparations available at pet shops, and these are more convenient to use than the pure form. One should follow the manufacturer's instructions for treatment, as different manufacturers use different concentrations of the active ingredient.
METRONIDAZOLE -- used to control flagellated protozoans and can be delivered in a medicated food or as a bath if fish are not eating. A concentration of ~7 mg/L can be administered daily for 5 days. A daily water change a few hours after treatment is recommended. Metronidazole can be administered at 50 mg/kg delivered in food, for 5 days. Anecdotal information suggests that excessive treatment (10 times the recommended dosage for 30 days) with metronidazole may be associated with reproductive failure in some fish.
MINOCYCLINE -- (see Doxycycline)
MS 222 (3-aminobenzoic acid ethyl ester methanesulfonate salt) -- in carbonate buffered aquaria water. Rainbowfish can be anaesthetised by bathing for 3 mins in a concentration of 150 mg/L.
NIFURPIRINOL -- this nitrofuran compound is commonly used, and effective, against many aquarium microbes: as a dip, at 1 to 2 mg/L for 5 min to 6 hours; as an immersion, at 0.1 mg/ L for three to five days.
ORGANOPHOSPHATES -- drugs of this group are used to treat a wide assortment of metazoan ectoparasites; there are a number of such compounds in this classification, but the ones practicing veterinarians are most likely to find useful are dichlorvos and trichlorfon in a variety of concentrations and combinations; trichlorfon is used as an ectoparasiticide effective against flukes, fish lice, and anchor worms at a dose of 0.2 mg/L active ingredient as a permanent treatment, or as a 2 to 2.5%, five to ten minute dip; trichlorfon degrades to dichlorvos (the antiparasitic entity) and further to dimethyl-hydrogen-phosphate in aquarium water—this chain is water pH and hardness dependent—faster in hard, alkaline water than soft, acid water.
PAPAIN -- use of a 0.2% solution in removing the gelatinous matrix of fish-egg masses in order to improve hatchability and decrease the incidence of disease.
PHENOXYETHANOL -- this drug has been used as an anaesthetic at doses of 0.1 to 0.5 ml/L [100 to 500 mg/L], and is also claimed to have antibacterial action; the biological activity is temperature-dependent and lower doses can be used at lower water temperatures; there is a narrow margin of safety and 2X doses will kill fish.
POTASSIUM CHLORIDE -- used as an aid in osmoregulation; relieves stress and prevents shock. Dosages used would be those necessary to increase chloride ion concentration to 10–2000 mg/L.
POTASSIUM PERMANGANATE -- for use against ciliates infecting the skin; use 4 mg/L in a bath for 30 to 60 minutes.
POVIDONE IODINE -- 100 mg/L solution for 10 minutes as an egg-surface disinfectant during and after water hardening.
Iodine compounds are basically a complex of iodine with a solubilising agent or carrier that liberates free iodine in solution. Iodine, like chlorine, is a halogen and has a strong oxidising capability. It is lethal to microflora and to viruses, which are killed within 15 min in a 50 ppm solution. Like chlorine, iodine compounds can be used only for disinfection and is too toxic for treatment or prophylactic purposes. However, it has a much lower toxicity as compared to chlorophors (such as hypochlorite) and thus can be used to treat eggs of shrimp and fish. In addition, iodine compounds are not inactivated by organic matter to the extent that chlorine is. Even a solution as dilute as 10% iodine will exert adequate bactericidal action in the presence of organic matter. Iodine compounds have been found to be effective against bacteria and fungi on fish eggs in aquaculture.
PRAZIQUANTEL -- useful against tapeworms and monogenetic flukes; at a dose of 2 mg/L, this drug has been shown to remove tapeworms within one hour, and external flukes within one day.
Praziquantel has been identified as the most effective “in water” treatment of infected fish. Praziquantel is harmless to fish of all species, is non toxic to plants, and has no negative filter impact. Praziquantel is a bitter tasting powder which shows good absorption directly from the treated water, and then admirable clearance of various surface and internal flukes and worms in fish. Praziquantel has been known to the hobby for many years. Praziquantel was traditionally available in the form of branded Droncit® tablets, for oral administration in dogs and cats, but is now available in a range of aquarium products.
Praziquantel used at 2–3 mg/L is very effective for control of both gill and body flukes and has a wide margin of safety for fish. Praziquantel is toxic to flukes on contact, paralysing the parasites within 15 seconds under laboratory conditions. Praziquantel preparations must be dosed high enough and long enough for effective treatment. Monogeneans can be persistent in aquarium systems necessitating regular treatments. In cool water, the parasites move through their life cycles slowly, so it is important to medicate long enough to intercept the emerging larvae. When temperatures are above 25º Celsius, treat once every 3 to 4 days for a total treatment time of 20 days. When temperatures are between 20 and 25º Celsius, treat once every 4 to 5 days for a total treatment time of 25 days. The eggs can be resilient to chemical treatment, which make the use of multiple chemical treatments appropriate to control this group of organisms.
Praziquantel can also be administered in food at a dosage of 35125 mg/kg for up to 3 days or as a short-term bath treatment at a concentration of 10 mg/L for 3 hours.
Change 50–75% of the water in between the chemical treatments. Fish, which are obviously weak and heavily parasitised may not survive. Management to lessen the chance of infestation by these parasites includes maintaining the fish in a good nutritional state and avoiding water quality problems that might weaken the fish.
The effectiveness of the long-term use of Praziquantel has been evaluated in ornamental fish. Cumulative doses up to 10 mg/L water were tolerated without side-effects by Angel Fish (Pterophyllum scalare), Discus, and a variety of catfish species (Ancistrus sp., Corydoras sp.). It was found appropriate to start with a dosage of 2.5 mg/L and to add the same dosage every other day several times.
All adult parasites and larvae were killed by this treatment. For the complete elimination of Dactylogyridae populations in a closed aquarium system, 3 therapy-cycles (duration: 5-6 days, accumulated dosage: 2.5 mg/L/day) proved to be effective. It was important to interrupt the therapy-cycles with intervals without medication (1 to 4 weeks). However, there are reports that kissing gouramis (Helostoma temminckii) have been adversely affected by Prazifish® (Praziquantel 98.5 mg/g).
SODIUM BICARBONATE -- 142 to 642 mg/L for 5 minutes [or to effect] as a means of introducing carbon dioxide into the water to anaesthetise fish [higher doses to euthanize fish].
SODIUM CHLORIDE (NaCl) -- also known as salt, has many potential applications in fish keeping. It effectively controls some parasites and minimises osmoregulatory stress. Immersing rainbowfishes in a salt concentration of 30 g/L of water for 10-30 minutes may effectively eliminate some parasitic infestations (stop the treatment earlier if the fish show signs of stress). Weaker solutions containing 5 to 10 grams per litre of water may be used as a bath for several hours to eliminate some freshwater parasites.
The use of ordinary salt (or sea water) was among the first of the methods proposed to combat fungal disease. Often, the application of salt either directly onto the diseased part of individual fish, or as a solution in which to bathe the fish. Salt can be used at 10 g/L for 20 minutes for young fish and 25 g/L for 10–20 minutes for older fish. A continuous well-aerated salt bath of 2–5 g/L may assist in recovery by preventing fungal infections. However, there appear to be significant differences among species and possibly families as well in the tolerance of the larval and fry stages to salt. 0.5 to 1% solution for an indefinite period as an osmoregulatory aid for the relief of stress and prevention of shock in fish. A 0.3 to 0.5% solution will control Hydra; a 10 to 15 min bath in a 2 to 3% solution facilitates the removal of leeches.
Salt is very effective against Trichodina, at a rate of 0.3%, added 0.1% every 12 hours for 3 treatments. Some strains have been found to be resistant against salt, so another choice of treatment would be Quick Cure® or any other medication containing Formalin.
Care must be exercised to avoid over treatment, which will place the fish in the same condition of osmoregulatory shock. Water constantly enters the body of freshwater fish because their body fluids have a higher salt content than the surrounding water. Salts will move from areas of high concentration, (blood), to low concentration, (fresh water), by diffusion. While the skin is moderately watertight because of a mucus coating, the gills and oral membranes allow water to pass through passively. Therefore, although these fish drink very little water, by controlled elimination they must excrete large volumes of urine and take in salt to maintain an osmotic balance within the narrow limits necessary for life. Any physical damage to the external tissues allows increasingly more water to enter the body, (and salt to escape), placing an additional burden on the kidneys. With just moderate injuries, this can become too much and the kidneys will fail causing death.
The blood salt content of rainbowfishes is approximately 9 g/L (0.9 percent), and an average pH 7.4. Almost 80 percent of this blood salt is sodium chloride, (NaCl), the remainder made up of bicarbonate, potassium and calcium. Sodium and potassium are vital for normal heart, muscle, and nerve function, excessive loss causing heart failure plus muscle and nerve spasms. Damage and stress caused by capture and handling of fish results in the loss of salt which must be replaced. This replacement is an active process requiring body energy from an already stressed and weakened animal.
The salt addition must be exact and monitored: 10 g/L of NaCl is 10 percent higher than the total blood salt content and may cause some water loss and salt diffusion into the blood resulting in dehydration. 7 g/L is slightly lower than normal blood and is probably optimal for holding and shipping water: dehydration will be avoided, salt loss will be low, and the kidneys will be active but not overloaded. However, those species not adapted to elevated salt content may not tolerate this concentration and more dilute salt solutions should be trialed. By understanding the need to maintain a water balance in freshwater fish, one can understand why using salt during transport is beneficial. Most freshwater fish can tolerate a salt concentration of 1–3 g/L, and this level is not harmful to the biological filter.
Salt Solution 1 gram/Litre water = 0.1% 10 grams/Litre water = 1%
SODIUM SULPHITE -- use a 15% solution for 5 to 8 minutes on fish eggs to improve their hatchability.
SODIUM THIOSULFATE -- used to remove chlorine from aquarium water; there are many commercial preparations available (follow package directions); in instances where chlorine and chloramine are bonded and both contained in the source water, sodium thiosulfate will break the bond and detoxify the chlorine but leave the ammonia, which then must be removed.
TOLTRAZURIL -- for use against ciliates infecting the skin and gills; reported to be active against trophozoites if used at a dose of 10 mg/L for two hours on day 1, then 20 mg/L on days 2 and 3.
TRICHLORFON -- (Case Report) An ornamental fish and aquarium plant producer noted approximately 50% of fish in a pond to be swimming in erratic circles, apparently due to having bent bodies varying from subtle to extreme. The pond was primarily used for plant production, and contained mixed species and sizes of rainbowfishes. All affected fish were the pygmy rainbowfish (Melanotaenia pygmaea) that were greater than 5–6 cm in length. One affected fish was submitted to Berrimah Veterinary Laboratories for evaluation.
At gross necropsy, spinal curvature in the dorso-ventral plane of the proximal tail region was noted. Histological examination revealed severe alteration in the normal size, shape and cellular organisation of one region of the spinal column. There was fragmentation and collapse of a vertebral body with associated fibrosis and irregular bony proliferation, consistent with earlier fracture of the vertebral column and attempts at regeneration. Adjacent muscle fibers were necrotic. There was no evidence of an infectious cause, such as bacterial, fungal or parasitic infection of the affected tissue to explain the lesions.
Subsequent close questioning of the producer revealed that the pond had been treated repeatedly in the past weeks with an organophosphate pesticide containing trichlorfon, at a rate of 0.5–2 ppm, to control aquatic invertebrate pests. Organophosphate pesticide exposure of fish occurs relatively commonly, either inadvertently, due to environmental contamination, or deliberately, for treatment for fluke, leech and crustacean fish ectoparasites.
Organophosphates commonly used to treat fish are trichlorfon and dichlorvos. When added to water, trichlorfon degrades to the more toxic dichlorvos, a process that is influenced by light, high water temperature and high pH. Also, organophosphate uptake and toxicity in fish is increased by low oxygenation of the water. These factors result in variable response of fish to exposure to organophosphates, with levels greater than 0.1 ppm being potentially toxic.
Organophosphates exert their toxic effect by inhibition of acetylcholinesterase, an enzyme involved in terminating neurotransmission at cholinergic synapses in the central nervous system, some peripheral autonomic junctions and neuromuscular junctions. In intoxicated fish that don’t die acutely from central nervous system dysfunction, the muscle spasms produced by excessive and prolonged stimulation of neuromuscular junctions of the muscles of the body are thought to be sufficiently severe to result in spinal fracture and lesions as seen in this case.
UREA AND TANNIC ACID -- used to denature the adhesive component of fish eggs at concentrations of 15 g urea and 20 g NaCl/5 litres water for approx. 6 minutes, followed by a separate solution of 0.75 g tannic acid per 5 litres of water for an additional 6 minutes.