Unit 17: Viruses and bacteria in the aquarium

Viral diseases Viruses are infectious bodies that replicate inside the cells of living things. Different viruses infect literally all types of organisms: animals, plants, and bacteria. They cannot replicate themselves without invading a host cell. A typical virus is a hundred times smaller than the average bacterial cell and can’t be seen through a regular microscope. Viruses spread in a variety of ways. Through direct contact, through water, by being eaten, or passed in faeces. Each type of virus has a range of host cells that it is able to infect. Some viruses can infect many different species, while others can infect only a few closely-related types of fishes.  

Viral diseases Lymphocystis is a common viral disease of freshwater fish. It’s more likely to appear when fish are stressed. The fish starts growing small white growths on its fins or skin and this is often mistaken for whitespot (Ich) in the early stages. It clumps together to form a cauliflower-like growth on the skin, fins, or gills. There is no known treatment. Surgery is sometimes tried. The growths may inhibit the fish's ability to swim, breathe or eat. If the fish is given a stress-free life the virus will slowly subside. This can take many months.

Lymphocystis

In many ways this disease is similar to chickenpox in humans. Carp Pox In an aquarium only goldfish or more often small carp will suffer from this viral disease. This is a herpes-type virus (Herpesvirus cyprini) that causes raised grey or white lumps (papillomas) that are unsightly, but rarely fatal. Occasionally there is a problem with secondary bacterial infections of the open sores. Eventually the disease goes into remission as the fish develops immunity to the virus, but some fish develop permanent scarring. In many ways this disease is similar to chickenpox in humans.

Carp pox

Control of viral diseases If you suspect that a fish is infected with a virus, limit its spread to other fishes. Nets or any other aquarium equipment exposed to the water in a contaminated aquarium must be sterilised before re-use in another aquarium. A disinfecting solution can be prepared by mixing one part basic bleach to nine parts tap water. Nets and tank tools are dipped in this solution for ten minutes rinsed well with tap water and hung up to dry. There is no cure for viral diseases, all you can hope for is that it will recover on its own. You can help this process along by giving the fish the best possible care during the time it shows symptoms of the infection.

Bacterial diseases Bacteria are present everywhere on land and in the water. We talk about bacteria as either 'good' or 'bad'. ‘Good’ bacteria in the aquarium are found in the biological filter and break down ammonia. ‘Bad’ bacteria are constantly present but do not cause problems until the fish is injured, stressed, or already ill when they take advantage.

Cause: Aeromonas, Pseudomonas, and Flexibacter bacteria. Fin rot Fin rot may begin with red streaks in the fins then an abnormal lightening of the edge of the fin, followed by fraying or rotting of the fin membrane and edges. This can lead to a complete rotting of the fin and can spread to the body and lead to death. Cause: Aeromonas, Pseudomonas, and Flexibacter bacteria. The bacteria are already in the water, but do not cause problems in healthy fish. Injury to the fins, stress, or poor water quality can all lead to an increase in these infections. Treatment: Infected fish can be bathed in a salt solution (if the fish can tolerate it) or a shop bought treatment. In the UK antibiotics are only available from a vet.

Fin rot

Cause: Flexibacter columnaris Mouth rot The disease begins with white marks on the head, fins, or gills. The lips may be involved and the inside of the mouth. The lesions grow to resemble white, fluffy, fungus-like tufts coarser and greyer in colour than most fungal infections. Cause: Flexibacter columnaris Transmission: The bacteria are commonly present in aquarium water. Any existing injuries or diseases of the mouth, incorrect PH, high levels of nitrate, low oxygen concentrations, or even a vitamin deficiency, can set it off. Treatment: Put the fish in a quarantine aquarium and add an antibacterial treatment. Vets may prescribe antibiotics.

Mouth rot

Fish TB Very common. Fish show a loss of appetite, pale skin, emaciation, lethargy, skin ulcers, and general poor health. It can lead to skeletal deformities (a bendy body). Cause: Mycobacterium The bacteria can be transmitted in the water from open ulcers, faeces of infected fish, or by fish eating infected dead fish. This disease is often associated with poorly kept or dirty tanks and poor water quality. Dead fish should quickly be removed and disposed of. Diseased live fish should be removed to a treatment tank. Treatment: Very difficult in the UK as it needs antibiotics. All infected fish should be handled with care to prevent transmission to humans through open wounds or cuts.

Fish TB

Ulcers Ulcers usually show up as raw areas in the skin, with reddened edges. Many disease problems can set them off. Causes: Aeromonas, Pseudomonas, Mycobacterium, and Vibrio all of which are commonly found in the water and will invade a wound or skin injury. Previously damaged skin, poor water conditions, and stress can all lead to an increase in ulcers. Treatment: Proprietary treatments for external bacteria often backed up with anti-fungal treatments. Improve water quality, reduce stress, and decrease the risk of injury.

Ulcers

Eye problems Popeye, or exophthalmia, is swelling of one or both eyes of the aquarium fish. If a fish has popeye a bacterial disease may be the cause. Fish tuberculosis, Mycobacterium marinum is a possibility. One or both eyes of the aquarium fish bulge outwards and the outer surface may be white or cloudy. It can be unilateral (just one eye affected) or bilateral. The swelling is caused by fluid leaking into the region behind the eyeball. Treatment: Internal bacterial infections are hard to treat. Improve the aquarium conditions. A vet may prescribe antibiotics.

Popeye

A very poorly fish Bent spine TB Fin rot White spot Fungus Protruding popeye Ooo ooo ooo Lymphocystis Constipation Mouth rot Anchor worm Raised scales dropsy Ulcer Tumour