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