Disease Prevention

Successful fish health management begins with prevention of disease rather than treatment. 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.

Perhaps the first consideration in preventing fish disease is effective quarantine. Quarantine is a period of isolation during which the fish are observed for any disease. Fishkeepers rarely quarantine fish because to do so would require extra aquaria, expense, and time. However, 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. It 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. A quarantine period of 3-4 weeks is suggested.

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 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 be used. 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. Procedures for equipment sterilisation are explained later in this chapter.

Beneficial Effect of Quarantine:

1. Evaluation of the health condition of the new fish.
2. Diseases in stage of incubation may become manifest days or weeks after an apparently healthy fish is acquired.
3. A quarantine tank allows a more effective observation of the fish than a community tank.
4. Reduction of disease transmission risk to pre-existing fish.
5. 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.
6. More gradual acclimatisation of the new fish.
7. A community tank is often a highly competitive environment where new fish are at disadvantage.
8. Administration of drugs is convenient.
9. Quarantine tanks are often smaller than the community tank, and fewer drugs are needed (if dissolved in water).
10. Less organic material that may inactivate the active medication.

Rainbowfishes maintained in aquaria are increasingly subject to disease. Increased organic load, associated with inappropriate feeding and stocking rates, creates an environment where opportunistic bacteria, fungi, and parasites can flourish. To minimise this, water exchange should be adequate for the stocking densities and feeding rates.

Particulate matter (faeces, uneaten food, dead plant material etc.) should be removed on a regular basis. This includes removal of debris by syphoning, manual removal of algae from tank walls, and regular cleaning and removal of particulate matter from the filter. Equipment should be disinfected between use in different tanks and any sick or dead fish should be removed promptly, as they are an important means of transmitting infectious disease to other fish in the system as well as adding to the organic load as they decay.

Cleanliness is one of the cornerstones of fish health management. A number of infectious diseases, particularly fungal infections, may be directly attributed to accumulation of organic material in the aquarium. It is important that syphon hoses, nets, brushes, and other equipment used to clean tanks should be treated with a sterilising solution agent after use. An easy way to achieve this is to have a plastic garbage bin into which equipment can be dipped or placed between uses. Items still in the bath after one hour or at the end of the day should be removed, rinsed with fresh water, and stored dry.

Chemicals used should be minimally toxic to fish yet be effective at removal of infectious particles and other organic debris likely to accumulate on equipment. Solutions of Chlorine and Potassium permanganate are effective for disinfecting equipment. Commercial disinfectants such as Benzalkonium Chloride or quaternary ammonium compounds are also suitable and should be used according to label instructions.

If using chlorine for disinfecting equipment or tanks which are not in use, but which are in the vicinity of others housing live fish, the granular form (Calcium hypochlorite 65%) should be used. Granular chlorine does not volatilise as readily as liquid chlorine (Sodium hypochlorite). In a poorly ventilated fishroom, fumes from liquid chlorine can cause fish kills in adjacent tanks. Chlorine fumes can also be harmful to the aquarist. Concentrations of 10 mg/L for 24 hours are effective for disinfections of tanks or submersed equipment. If equipment is to be disinfected by submersion in a chlorine solution, concentrations of 200 mg/L can be used for 30 to 60 minutes or 100 mg/L for several hours.

Use chlorine with caution as repeated use and extended exposure of the silicon sealant to chlorine will destroy or render the adhesive bond ineffective on glass aquariums with disastrous results. Chlorine will dissolve synthetic material like sponge filters. Always wear eye protection and rubber gloves when handling large quantities of chlorine. Calcium hypochlorite is an oxidising agent and should not be exposed to intense heat, acids, or organic compounds because it is a fire hazard, particularly if wet. In some cases, explosion may occur. Chlorine residue can be neutralised by using 7.4 mg/L Sodium thiosulfate for each 1 mg/L chlorine present in solution (7.5 grams of Sodium thiosulfate will neutralise the chlorine present in 5 litres of a solution of 200 mg/L).

Potassium permanganate (KMnO4) breaks down organic matter and certain chemicals in water. Because it is so destructive, it must be used carefully to avoid personal injury and damage to fish. Bacteria, fungi, external parasites, and any other form of life can be killed if exposed to a high dose. Certain materials may deteriorate after repeated exposure to Potassium permanganate. Rubber and synthetic or natural fibres may degrade rapidly, but most plastics are unaffected.

Potassium permanganate dust and solutions can burn and irritate skin. Wear face mask and protective rubber clothing. Be careful to ensure your eyes are protected, and wear rubber gloves. Store in a cool; dry place, preferably on a concrete floor. Formaldehyde (formalin) and potassium permanganate may react together to form toxic formaldehyde gas, particularly if they are in concentrated forms. Potassium permanganate, like Calcium hypochlorite, should not be exposed to intense heat, acids, or organic compounds because it is a fire hazard. In some cases, explosion may occur.

Regular control and monitoring of water quality is imperative and will greatly reduce the likelihood of a disease occurrence. Critical water quality parameters include temperature (particularly sudden and dramatic shifts), dissolved oxygen, pH, alkalinity, hardness, nitrogenous wastes, and toxic substances. Water quality should be monitored frequently and corrective measures initiated if conditions become unfavourable. It's important to become familiar with water testing and have the necessary test kits available.

Other preventive measures are to stock fewer fish per aquarium and change water regularly. Be sure to precondition the water before adding it to your aquarium. Also, remove any sick or dead fish promptly, as they are an important means of transmitting infectious disease to other fish in the system.

Aim to keep your ammonia and nitrite at zero levels, and nitrate down to a minimum. Nitrate levels over 20 mg/L (ppm) can cause problems with excessive algae growth and can lead to fish health problems in the longer-term. Optimum water conditions must be maintained at all times. Sub-optimum conditions, while not immediately lethal, may stress the fish, resulting in delayed mortality. Light (excessive or rapid changes in intensity), noise and other disturbances can also stress fish and should be minimised.

The use of a good quality food will provide the fish with all the nutrients that they need to remain healthy and to grow. Rainbowfishes fed a nutritionally complete diet are better able to cope with stress and to resist disease. However, you should note that even good quality food will deteriorate if improperly stored or kept too long.

Storage time for most commercial fish foods will vary depending upon environmental conditions; however, as a rule of thumb, 90 days is normally the maximum safe storage time for fish feed. Fish foods should be stored in a cool and dry place (refrigerator), and used within 30 days of opening. Never feed mouldy, discoloured or clumped feed. Moulds on feed may produce aflatoxins, which can kill fish.

© Copyright Adrian R. Tappin
Created July, 2005.