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Successful fish health management begins with prevention of disease rather than treatment. Fish health management can be as challenging and complex as the actual control of existing diseases. Prevention is accomplished through good water quality management, nutrition, and cleanliness. Without this foundation, it is impossible to prevent outbreaks of opportunistic diseases. Even the use of sterilisation technology; for example, ultraviolet sterilisers and ozonisation, does not eliminate all potential pathogens from the aquarium environment. Key elements of disease prevention include the reliable detection of disease carriers, knowledge of how pathogens are transmitted, and development of effective methods to limit the entry of pathogens or carriers into uncontaminated aquariums, and the capability to provide environmental conditions conducive to good health.
Direct contact between fish is, except at breeding and during territorial disputes, rare in nature. In captivity, dense stocking in aquarium systems or transport bags and catching fish in nets may mean direct contact is an important route of disease transmission. When ornamental fish are sold by retail stores to the public, the fish and a volume of their aquarium water is generally transferred to a plastic bag. Although this allows the fish to be transferred to the purchaser's aquarium, it also represents one means by which the aquarium fish could be exposed to pathogenic organisms. The aquarium water supplied with ornamental fish purchased at retail outlets may contain significant numbers of a wide variety of pathogens.
Avoidance of exposure to disease is the primary method of prevention and the first consideration in preventing fish disease is effective quarantine. Proper and appropriate quarantine is a vital component of any successful fish health management program. There are several beneficial reasons for using quarantine before placing rainbowfishes into their final aquarium. First of all, newly arrived fishes can be isolated so their overall health condition can be properly and thoroughly evaluated and examined. Secondly, prophylactic measures can be taken and already diseased fishes can be isolated to prevent further spread of the problem. A quarantine tank also provides an easier way to treat diseased fishes rather than treating them in the main aquarium.
The term quarantine is defined as "isolation imposed on persons or animals that have arrived from elsewhere or been exposed to, and might spread, infectious or contagious disease". It is derived from the Italian quarantina, which means forty days. Quarantine (that is a forty-day period of isolation) can be applied to any animal, but was originally applied to humans and warm blooded animals. The expectation was that forty days (or other period of time stipulated by law) would be longer than the incubation period of serious diseases like small pox or rabies. Thus any infected animal would become identifiably unwell in that period.
Fish are not warm blooded, and their diseases do not have incubation periods that are similar in all conditions. Fish adopt the temperature of the water that surrounds them. If their environment is temperature stable, then the incubation period of a disease may be predictable. However, most fish are subject to quite wide fluctuations in temperature, and there are wide differences in incubation periods for diseases across this temperature range.
The length of quarantine should reflect the length of time required for disease entities common to the species to be detected, either via diagnostic procedures or clinical manifestations. Ideally, new fishes should be held in quarantine for at least 30 days. A period of at least 30 days should be adequate for most parasite problems to become apparent, as well as those caused by most bacteria. The same applies to plants, rocks and driftwood, which may also carry fish pathogens. Nevertheless, it must be recognised that certain species or disease problems may require more time.
Furthermore, to avoid or improve the possible consequences of environmental and physiological stress, an acclimatisation period may be useful. An acclimatisation period will let the fishes adjust to the new environmental conditions. Acclimatisation of new fishes should ideally begin before they arrive. This may involve acclimatisation to the temperature of the water, the light intensity, the pH, the chemical condition of the water and their new environment. It is important to know as much about the quality (i.e. temperature, pH, hardness, etc.) of the water from which the fishes are coming. This way the environment in the quarantine tank can be adjusted to match the old environment. If need be, once the fishes have settled in, these parameters can be changed in small steps. Acclimation can be considered complete when the measurable parameters are the same (or at least similar) as those in the main aquarium. Disturbing the fishes as little as possible and keeping the lighting low will help reduce stress.
A quarantine system should be very simple so that fish are readily accessible for observation and handling, water can be easily changed, and treatments readily administered. A quarantine tank should be bare, with just a few plastic plants if the fish requires cover to prevent or reduce stress and a pre-cycled sponge filter. Quarantine tanks can be intrinsically more unstable than an established tank, and the importance of adequate water changes should not be underestimated, unless contraindicated by the treatment therapy being used. The walls and bottom of the tank should be kept as clean as possible. Even apparently minor slime coating (biofilm) on the glass can hide massive amount of microorganisms which are capable of causing health problems. A reliable and adequately powered heater with easy-to-adjust temperature settings should also be used. Ideally, rainbowfishes should be quarantined at a temperature of 22-25° Celsius.
A suitable quarantine tank should be available at all times. Such a tank doesn't need to be any larger than 50 litres and can be set up and maintained just like any other aquarium. This has to be done in such a way, as to prohibit physical contact, to avoid splashing and water contamination, or aerosolisation. Aeration and splashing creates small water droplets than can become suspended in the air as an aerosol. Aerosols can contain small pathogens such as bacteria and viruses. Particularly in humid environments aerosols can be long lived and thus act as a transmission agent for diseases between holding systems. Ichthyophthirius multifiliis and Aeromonas salmonicida have been shown to be transported by aerosols. Aerosol droplets persist longer in damp or humid conditions. Aeromonas spp. bacteria have been known to spread at least seven metres in aerosols. That was the size of the room in which the experiment took place and may not represent the distance the bacteria could travel in ideal conditions.
The quarantine tank should remain empty to receive new arrivals for the purpose of quarantine, and to take in any diseased fishes from the main aquarium(s) should the need arise. As a precaution against transmission of diseases, nets, syphoning equipment, buckets, and any other equipment used in the quarantine tank should not be utilised for any other tank.
Benefits of Quarantine:
- Evaluation of the health condition of the new fish.
- Diseases in stage of incubation may become manifest days or weeks after an apparently healthy fish is acquired.
- A quarantine tank allows a more effective observation of the fish than a display tank.
- Reduction of disease transmission risk to pre-existing fish.
- Although pathogens may be transmitted to other tanks by contaminated equipment (nets, etc.) or even by air-borne particles, most bacteria and parasites remain contained to the quarantine tank until proper treatment eliminates them.
- More gradual acclimatisation of the new fish.
- A display tank is often a highly competitive environment where new fish are at disadvantage.
- Administration of medication or chemicals is convenient.
- Quarantine tanks are often smaller than the display tank, and fewer chemicals are needed (if dissolved in water).
- Less organic material that may inactivate the active medication.
Nevertheless, many aquarium hobbyists are not convinced of these benefits and show no interest in using or developing quarantine protocols. It should, however, be understood that while quarantine procedures greatly reduce the problems associated with the acquisition of new fish, there is no guarantee that any problems will be eliminated. Some diseases may have such a prolonged incubation period that it takes months before symptoms appear. In other cases, a new fish may simply be an asymptomatic carrier of an infectious disease. This means that the carrier does not show signs of the infection although a potential pathogen is present, and the quarantine is completed with no problems. However, other fish later infected by the same agent in the main aquarium may start to manifest symptoms.
© Copyright Adrian R. Tappin
Created July, 2005
Updated December, 2008
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