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Disease recognition and treatment


The outbreak of disease in an aquarium is serious, especially for the new hobbyist who is generally inexperienced in recognition and control of fish diseases. The best approach to control is always prevention, by providing proper environmental conditions, and a good program of aquarium maintenance, a sound diet, and the use of other preventive measures.
To prevent disease outbreaks it is important to understand how diseases occur. Disease is a process initiated by reduced resistance of the fish. It is a disruption of the delicate balance involving the fish, and the environmental conditions, and the disease agents. Research to date shows that the disease process can be initiated by exposure to unfavorable environmental changes such as temperature fluctuations, persistent ammonia concentrations, low oxygen levels, overcrowding, and inadequate diets.. Each of these factors can play a role in the initiation and development of a disease.

Disease recognition

Sick fish alter their normal behavioral patterns in response to a disease or or environmental changes. Often the sign observed is not specific, but indicative of either infectious disease or non-infectious water quality or nutrition related problems. Some disease signs, such as the presence of a parasite on the fish's body, are specific and easily recognized as a sign of infectious disease. For the inexperienced aquarist, caution must be observed in attempting to diagnose a disease problem.
Diseased fish are recognized by various signs, including increased respiration rate, scratching on objects or the aquarium bottom , pale coloration, refusal to eat, frayed fins, appearance of body ulcers, cloudy eyes, and other signs. These signs do not necessarily indicate the specific cause, only that a disease problem is developing. Pale color, for example, could be caused either by improper nutrition, the early stages of an infectious disease, or poor water quality.
The following nonspecific disease signs are commonly associated with marine fishes affected with a disease.

Increased Respiration:

Fish have a abnormally high rate of breathing, with a tendency to stay near the surface or areas of high water agitation. Possible Causes: Water Quality problem such as low oxygen concentrations, high ammonia, or high temperature are the likely cause of increased respiration. However the fish could also be infested with external parasites.


Marine fish scratch or rub themselves repeatedly on objects in the aquarium or on the aquarium bottom . Possible Causes: Continual scratching is most often associated with parasitic infestation.

Clamped Fins:

The affected fish will tend to hold it's fins close to the body proper. Frayed fins can sometimes be observed. Possible Causes: Most fish erect their fins during swimming, thought this behavior varies. Fish that tightly clamp their fins and appear to be listless could be in the early stages of disease. If frayed fins are also present, it could indicate that the fish had been in a fight with another fish in the aquarium.

Lack of appetite:

This sign is common and can be caused by various factors. Affected fish refuse to feed or abruptly stop feeding. Possible Causes: Refusal to eat can be related to feeding a improper food, such as feeding dry food to a fish that only accepts live foods. When fish suddenly stop feeding, it could indicate the early stages of a infectious disease. When this occurs after the introduction of a new aquarium fish, it can be related to the fright response or to aggression by tank mates.

Pale Color:

Fish lose their natural coloration and become pale. Possible Causes: A short-term change in color is normal and can be related to a fright response. This can occur when fish are moved from one tank to another. Chronic pale color can be related to development of disease or poor nutrition. Chronic abnormal light color can also indicate blindness.

Cloudy Eyes:

With this easily recognizable sign, either one or both eyes become cloudy. Possible Causes: Physical injury related to capture or netting is not uncommon with new fish. The development of a cloudy eye can also indicate physical injury caused by fighting. This condition is often temporary, while extensive physical damage can result in permanent injury. Cloudy eyes can also be a sign of bacterial or parasitic disease.

Frayed Fins:

The fins are either frayed or shredded . The base of the fins have a reddish appearance. Possible Causes: This can be caused by injury from fighting with tank mates or can indicate the early stages of a bacterial or other infectious disease.

White Spots on Body:

Affected fish have irregular distribution of white spots over their body, Possible Causes: This can be caused by a external protozoan parasites or by adherence of fine particulate matter or air bubbles in the mucus.

Ulceration of Body:

Small to large ulcers on the body may have pale areas and a reddened perimeter. Possible Causes: Ulcers may indicate bacterial infection and/or parasitic infestation.

Disease Problems and Their Causes

It should be now be known that various disease signs can be caused by agents ranging from environmental abnormalities to biological causes such as parasites. Determining the exact cause is not always possible, but it is important to distinguish between diseases initiated by environmental problems and those caused by disease agents.

Say for example you have a aquarium with several types of fish. You notice that one of the fish has an increased respiratory rate. From the disease signs discussed earlier, this could be related to an environmental problem such as low oxygen concentrations or to parasites. How do you determine the exact cause of the increased breathing rate of the fish?

It is important not to assume immediately that the fish is infested by parasites until you are convinced that the rapid breathing is not related to the water quality. This is due to the fact that a great majority of problems, especially in new aquariums, are related to water quality. The best approach is first to perform a series of water tests, including pH, ammonia, nitrite, and others. Check to be sure that all filters and air stones are functioning properly. Ask yourself a few questions: When did I make the last water change? Are the results of the water tests within acceptable ranges? Did I add any new items such as coral or rock, which could be toxic or contribute to water pollution? Have any paints, or insecticides, or soaps, been near the aquarium?

If everything related to the equipment function and the environment appears to be normal, then it is likely that the cause is related to an infectious disease agent.

The example given was a simple one but it should give you a idea of how to use a problem solving approach.

Quarantine Period

Isolating new fish in a separate aquarium is a highly effective means of preventing the introduction of diseases to an established aquarium. Quarantine aquariums are often referred to as "Hospital aquariums" or "isolation tank". The process of quarantine requires a separate small aquarium that will be used exclusively for the isolation of new aquarium fish and invertebrates.

While a quarantine aquarium is not required during the first introduction of fish to your display aquarium, quarantine is recommend for future additions of fish to your main aquarium. The use of quarantine aquariums is based on the assumption that all fish carry some kind of disease agent, especially external parasites. During capture , holding, and transport, the marine fish are stressed, which in turn decreases their resistance to disease. If the diseased fish are added directly to an established display aquarium, they will transmit the disease agents to other fish.

Another benefit of a quarantine tank is that it allows new fish to acclimate to their new conditions in a less stressful environment. New fish directly added to an aquarium are often bullied by the established fish, making it more difficult for the new fish to acclimate.

Common Disease Problems

Health problems of marine fish can be caused by parasites, microbes, deterioration in water quality, or poor nutrition practices. By far, parasites are the most common and troublesome disease agents of the marine fish. The affect the fish by attaching to the skin, gills, or sometimes the eye. Other parasites are internal, where they invade the muscle, liver, or other organs. While some parasites are easily visible, others cannot be seen without a microscope. Microbial diseases are caused by bacteria, fungi, and viruses. Microbes are so small they cannot be seen with the naked eye. They are responsible foe a variety of diseases affecting marine fish. The most serious microbial diseases are caused by bacteria, which readily infect stressed fish.
Diseases can be initiated by poor water quality conditions, including high ammonia concentrations, low oxygen, improper ph, the presence of chloramines, or dangerous levels of other toxic chemicals. Diseases related to altered environmental conditions are not infectious, but chronic exposure to poor water quality can cause either immediate death or a secondary infection by bacteria.

Parasitic Diseases

Parasitic diseases are a major problem for aquarium fishes. Almost all marine fish have parasites to some degree. Protozoa's, small microscopic animals generally invisible to the naked eye, Are the most serious types of parasites. There are numerous parasites responsible for diseases of marine fish; I'll discuss the most common parasitic problems know to occur under aquarium conditions: Coral Reef Disease (Amyloodinium), White Spot Disease( Cryptocaryon), Clown fish Disease ( Brooklynella ), Black Ich ( Worm Parasites ) Flukes( Gill and Body Worm Parasites)

Coral Reef Disease:

Is the most common disease of marine fish, which can rapidly cause death if not treated promptly. The parasite primarily attacks the gills, body, and fins of the fish. The parasite, which is a small protozoan, is introduced into the aquarium through non quarantined fish.
The parasites appear as fine dust like white to yellowish spots, most readily visible to the naked eye on the transparent portions of the fins or dark pigmented areas of the body. Other signs associated with the disease include scratching on the aquarium bottom and on rocks, increased respiration rate, gasping near the water surface, pale color, and appearance of excessive slim on the fish's body.
The disease is rapidly transmitted from infested fish to other fish in the aquarium. During the life cycle of the parasite, it first develops on the fish's body (the host) and when mature drops to the aquarium bottom. The parasite encysts, then undergoes cell multiplication to form small free swimming parasites called dinospores. These young parasites are released from the cyst and infect other marine fish. Coral reef disease must be treated as soon as the disease is identified. A delay in treatment can result in the death of all your aquarium fish. The treatment of choice is through the use of ionic copper medications not chelated copper. Regardless of the brand of copper medication you use, it is essential that the treatment be not less than 14 days. The copper must be maintained within the range of 0.12 to 0.18 mg/L. Do not exceed the recommended concentration, as this could cause damage to your fish. Treatments using copper must never be conducted without the use of a copper test lit to monitor the concentration of copper during the treatment period. Keep in mind copper medications are toxic to invertebrates, if invertebrates are resent they must be removed prior to the treatment procedure. and should not be returned to the aquarium until the copper concentration drops below 0.03 mg/L.

White Spot Disease

Is also known as Saltwater Ich, affects the gills, fins, and the body of the fish. The parasite is introduced to the aquarium through the addition of infested fish. Fish infested with the disease develop randomly distributed white spots over the body and the fins. The white spots are considerably larger that the small dust like spots of coral reef disease. Diseased fish fish tend to scratch on aquarium objects, have a rapid breathing rate, congregate near areas of high water agitation, and stop eating. White Spot Disease is caused by a small ciliated protozoan that has a life cycle similar to that of the protozoan that causes Coral Reef Disease. After the attached parasite matures it drops to the bottom of the aquarium, and encysts. While encysted, free swimming parasites develop and are released into the aquarium water. The free swimming parasites are then able to infect aquarium fish. White Spot Disease is treated with copper based medications as out lined for the treatment of Coral Reef Disease. However for complete eradication, the treatment must be maintained for no fewer than 21 days, rather than the 14 days for Coral Reef Disease. White Spot Disease tends to be more difficult to eradicate, hence the necessity for an extended treatment period. 

Clownish Disease

Is a serious malady affecting clown fish or sea horses, and other kinds of marine fish. Various species of clown fish are particularly susceptible to infection from this parasite. The disease is caused by a small ciliated protozoan invisible to the naked eye. It is a parasite of the gills and skin, and unlike the other protozoa's discussed, the life cycle is simple, with the parasite reproducing by cell division. As a result the parasite multiplies rapidly on affected fish, causing mortalities in a short period of time. Affected fish develop body lesions, excessive slime secretion, and increased respiration. In the early stages of the disease all that is noticed is an abnormal paleness of color and a rapid breathing rate. As the disease worsens, lesions will be observed on the body, with sloughing of the skin and mucus. The development of a secondary infection with bacteria often accompanies infestation with the parasite. Clownish Disease is capable of killing fish within 24 to 36 hours after appearance of the signs of scratching and heavy respiration. Prompt treatment must be instituted if the disease is suspected. The parasite is sensitive to various medications, which can be purchased under various trade names. It is recommended that the fish with Clownish Disease be treated with medications that contain formalin or malachite green. Medications containing copper should be avoided, as the disease is not readily controlled by copper based chemicals.

Black Ich

Black Ich disease appears as small black spots distributed over the fish's body. The spots are about half the size of a pinhead or smaller. They are primarily found on the body and are are especially easy to see on light-colored body areas or on the transparent areas of the fins. Affected fish will scratch on the bottom or other aquarium objects. Other signs of the disease include lethargy, development of a pale body color, and lack of appetite. The disease is caused by a small worm known as a tubellarian. After parasitizing a fish, the worms develop on the fish's skin and gills and aquire dark pigmentation. They are freely mobile and will tend to move over the surface of the fish. After five or six days depending on the environmental conditions, they drop to the bottom of the aquarium. There they mature, with the development of the young worms within their body. Once the development of the young is complete, the adult worms burst, releasing the free swimming young that infest new host fish. The worms can be controlled with various commercially available medications. Formalin based products or those containing organophosphate compounds such as trichlorfon appear to be the best medications. In addition to the use of medications, any excessive buildup or organic material and debris should be siphoned from the aquarium several times during treatment. Since the young worms develop on the aquarium bottom, the removal of debris will aid in controlling the disease by reducing their numbers.


Flukes attach to fish by means of a special organ called a haptor, which is equipped with hooks, clamps, and anchors used to firmly attach the worm to the fish. Flukes are freely motile, moving over the fish's body or gills causing extensive damage to the fish through their movements. Flukes reproduce on the fish, with some species producing hundreds of eggs on the gills and body, which then hatch into free swimming larvae. The larvae reinfect the host fish or attach to other fish. Other fluke species are viviparous, meaning they give birth to living young rather than eggs. Affected fish show various abnormal behavior changes, including scratching, which is the most obvious sign of infestation. Other signs include increased respiration and change in body color. In sever infestations ulceration's may also be noticeable. These troublesome parasites can be controlled by various treatments, including freshwater dips, formalin-based medications or the use of ganophosphates. Freshwater dips are easily performed and often very effective in reducing the number of flukes on the body of the fish. Formalin-based medications and organophosphates have been used for many years with excellent success in treating flukes.

Water Quality Induced Diseases

As pointed out before maintaining proper water conditions is critical for ensuring the health and vitality of marine fish. Various disorders can be related to water quality problems.

Treating Serious Disease Medicine and quarantine will be necessary - treatment must begin immediately (a day makes a difference). Even with treatment there is only a 50% chance of recovery. Prompt treatment really makes the difference. Fortunately serious disease doesn't usually happen unless equipment failed or you made a mistake or neglected things (you'll almost always be the responsible party). Prevention is much better than disease treatment because the drugs themselves weaken and stress the fish, and moving them to a quarantine tank (and setting it up) is a lot of work for you also stressful to the fish - they might not eat just because they are in unfamiliar surroundings.

Most common causes of disease

You haven't been doing your water changes and the tank is filthy.

Starvation (giving wrong foods or could be due to bullying).

 Introduction of a new infected animal (adding new fish always carries some risk).

Major breakdown in equipment causing change in tank conditions that is not corrected (e.g. power outage more than four hours, stuck or badly set heater, or bacterial outbreak due to clogged/kinked hose).

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Hakob Arakelian
Copyright 2005 [Hakob Arakelian].