The usual fungus which affects fish is Saprolengia. It attacks
fishes already weakened by damage or parasites and is also liable to affect
newly purchased fishes if their new water conditions differ too widely
from their old tank.
Mouth fungus is actually caused by the slime bacterium Chondrococcus,
and may not necessarily respond to all fungus treatments : read labels
carefully to choose the right one, or consult your veterinary surgeon
about the possibility of using antibiotics.
Symptoms : Fungus infections appear as either white cotton-wool-like
tufts anywhere on the body or fins, or as an all-over dusty, cobwebby
Treatment : As with all the common fish diseases, proprietary treatments
are available from any aquarist's supplier. Calculate the volume of your
tank with this ready-reckoner and dose according
to the manufacturer's instructions. If your filter has carbon or carbon
foam in it, these must be temporarily removed for the duration of the
treatment as carbon will swiftly remove the treatment and render it useless.
Replace the carbon 48 hours after treatment is completed.
Healthy fish kept in good aquarium conditions rarely suffer from fin
rot. It is caused by bacteria invading the fins, often through damage
caused by bad handling or other bullying fish and is encouraged to
spread by poor water conditions and too low water temperature..
Symptoms : easily visible damage to some or all fins, especially
the soft tissues between the fin rays.
Treatment: a general aquarium clean-up is the main requirement,
and a regular check on water quality and temperature. Over-the-counter
"tonics" may help the individual fish to recover, but prevention
is the best course.
Scientific name Ichthyophthiriasis, hence the widespread use
of the common name. This is the most common of the fish parasites and
can infect even the best-kept tank. The Ich parasite lives out
its full life cycle within the fish tank; the parasitic stage attacks
the fish, then leaves the fish and forms cysts on the aquarium floor.
When these hatch, the free-swimming larvae find a new host and the cycle
Symptoms : Small white spots, rather like grains of sugar, appear
on the fishes' body, maybe even extending to the fins. These are particularly
conspicuous on dark-coloured fishes, such as mollies, Red-Tailed Black
Treatment : traditionally, Methyline Blue was the cure-all for
the commoner fish diseases including White Spot but more specific remedies
are now freely available. To treat White Spot you must dose your whole
tank, as the treatment works by killing off the free-swimming stage
of the parasite. Repeated treatments will be necessary to prevent newly
emerged parasites, which had been encysted during the initial treatment,
from causing renewed infection.
Calculate the volume of your tank with this ready-reckoner
and dose according to the manufacturer's instructions. If your filter
has carbon or carbon foam in it, these must be temporarily removed for
the duration of the treatment as carbon will swiftly remove the treatment
and render it useless. Replace the carbon 48 hours after the last treatment
is completed and the fish are disease-free.
This is another parasitic disease and the parasites responsible, Oodinium
limneticum and O. pillularis, have similar life-cycles to
the Ich parasite.
: Depending on which species of Oodinium is causing the disease,
the fish will be covered all over with either a fine golden or brownish
dust, giving a velvety appearance.
Treatment : Treat in exactly the same way as White Spot (Ich)
- remove any carbon filters and treat the whole tank - but using a treatment
designed to cure Velvet Disease.
Velvets responds rapidly to treatment with the correct remedy.
This is more of a physiological condition than an actual disease, and
some species - notably the common and popular Black Molly (Poecilia
hybrids) - are more prone to it than others. Once cause of this ailment
is a drop in water temperature so that the fish becomes chilled.
: Affected fishes make rapid undulating movements ("shimmying")
without making forward movement through the water.
Treatment : Check heating equipment for malfunction and adjust
the thermostat if necessary.
If making water changes, ensure that new water being added is the same
temperature as that already in the tank.
Fluid retention in the fishes body is known as dropsy, but the cause
of this condition is largely unknown.
: The distension of the body causes the fish scales to stand out noticeably
from the body, unlike the usual streamlined shape (fishes which have
just put on weight or are carrying eggs may be noticeably fatter, but
their scales will not protrude.)
Dropsy is difficult to cure although the fish may recover spontaneously.
The fluid from the fishes' body can infect the other fishes in the aquarium
so they must be quarantined at once.
Skin flukes (Gyrodactylus) and gill flukes (Dactylogyrus)
are parasitic flatworms which infect the skin and gills respectively.
Symptoms : Although very small, flukes are visible to the naked
eye to anyone with good enough eyesight.
Skin flukes burrow into the skin and cause loss of colour and generally
weaken the fish. Gill flukes cause obvious inflammation and the fish
struggle for oxygen, with an increased respiration rate and gaping gills.
(NB - fish gasping for breath at the surface will not necessarily be
suffering from parasitic infections but could well be gasping for oxygen
because an excess of carbon dioxide has accumulated in the water. Aeration
may bring immediate relief, but check your aquarium management for a
Treatment : Remove the infected fish to a treatment aquarium
or bowl, and treat with a proprietary remedy from your aquarists' supplier.
The parasites cannot live without a fish host, so while your fish are
being treated the parasites will die off if the tank is left uninhabited
for a few days.
diseases such as tuberculosis, threadworms and tapeworms are more
serious but produce no external symptoms until too late, and diagnosis
is usually via a post-mortem. Since this is outside the scope of the average
fish-keeper, I have not dealt with these diseases here.