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Bull. Eur. Ass. Fish Pathol., 26(1) 2006, 46
Internal diseases of ornamental fish:
a clinical approach
W. H. Wildgoose*
Midland Veterinary Surgery, 655 High Road, London E10 6RA, United Kingdom.
There are many diseases in ornamental fish that originate from the internal organs and which
are rarely mentioned in the hobby or scientific literature. The lack of professional involvement
and investigation, together with much anecdotal information and the irrational use of many
proprietary medications, has done little to further our knowledge in this important area of fish
health. Veterinarians are often asked to investigate these cases because the fish have a high
emotional value and have failed to respond to the proprietary medicines. These cases allow
veterinarians to use several professional skills and facilities which are commonly available in
general practice and frequently used with terrestrial animals.
In this workshop a brief summary of routine
diagnostic procedures was given to highlight
some of the unique aspects of investigating
ornamental fish health problems. The role of
advanced diagnostic imaging techniques such
as radiography and ultrasonography was
emphasised and several case studies were
used to illustrate the positive advantage of a
non-lethal approach to internal disorders of
fish. Both diagnostic and therapeutic aspects
of cases commonly seen in veterinary practice
were discussed.
Mouth deformity is often due to trauma and
can restrict normal feeding activity: a novel
corrective surgical procedure was briefly
described. Foreign bodies such as gravel or
other substrate can cause oral and gastric
obstructions, and manual removal under
anaesthesia may be required. Goldfish with
retrobulbar granulomas and retinal pigment
epithelial carcinomas were illustrated and the
variable success of surgical enucleation was
discussed with several participants.
Spinal deformity is common in orfe (Leuciscus
idus) and their sleek body shape may
predispose this species to spinal injury.
Several possible causes such as genetic
deformity, trauma, chemical toxicity,
electrocution and nutritional deficiency were
considered. Severe periosteal hyperplasia
with proliferative bone changes affecting only
the vertebrae in koi (Cyprinus carpio) is an
unusual and rare disease but similar to
hypervitaminosis A in cats, Paget’s disease in
humans and one of unknown aetiology
affecting snakes. In fish, it is not known if this
is due to bacterial infection, metabolic
disorder or exposure to environmental toxins
such as the herbicide, trifluralin but no
myxosporeans were found histologically in
one case that also had cardiomyopathy and
glomerulonephritis.
Abdominal swelling is common in coldwater
ornamental fish. The radiographic and
ultrasonographic features of polycystic
kidneys in goldfish (Carassius auratus) and
*Corresponding author’s e-mail: whwildgoose@aol.com
Bull. Eur. Ass. Fish Pathol., 26(1) 2006, 47
abdominal carcinomas in koi were shown.
Papillary cystadenoma of the collecting ducts
in oscars (Astronotus ocellatus) is a common
cause of abdominal swelling that result in
deformation of the swim bladder and
subsequent buoyancy disorders. The degree
of deformation and radiographic appearance
has varied substantially in the five cases
examined by the author.
Buoyancy disorders are particularly common
in some varieties of fancy goldfish and can be
due to several terminal diseases. Abnormal
buoyancy is exhibited by fish floating to the
surface or sinking to the bottom when at rest
or not actively swimming. This may be
accompanied by abnormal pitch (i.e. head up
or head down) or listing to one side or the
other. In many cases it has a sudden onset and
without any preceding traumatic event. Some
cases may have been affected for several days
or months before being presented for
examination. Tumours, polycystic disease and
large granulomatous lesions of the kidney can
cause unilateral displacement of the swim
bladder resulting in abnormal buoyancy.
Over-inflation of the swim bladder can occur
in fish with extensive granulomatous disease,
particularly if the cranial cavity is affected.
Fluid filling of the swim bladder has been
associated with bacterial and fungal infection,
which may then result in rupture of one of
the chambers. Pockets of retrobulbar gas and
increased contrast between the organs of the
body cavity are useful diagnostic findings in
radiographs of swim bladder rupture.
Excessive amounts of gas in the bowel causing
intestinal tympany can be due to bacterial
infection or obstruction and also result in
abnormal buoyancy.
Many cases of abdominal swelling or
buoyancy disorder do not recover but owners
are often keen to pursue some medical
management. This may include adding salt
(1-2 grams/ litre) to freshwater facilities,
raising or lowering the temperature, starving
for 2-3 days, or feeding a crushed garden pea
once daily. Some proprietary pet shop
medicines containing formalin and organic
dyes claim to be effective against bacterial
diseases of the swim bladder. Antibiotic
treatment by injection, immersion or
medication of food may also prove useful. In
cases of over-inflation, surgical reduction of
the swim bladder (pneumocystectomy) may
be successful although the benefit of
surgically implanting heavy foreign bodies to
add ballast is arguable.
It was hoped that this interactive case
presentation stimulated an interest to develop
a more professional approach and encourage
more scientific research to investigate the
wide range of internal disorders in pet fish.
Further Reading
Wildgoose WH (2001). BSAVA Manual of
Ornamental Fish, 2nd edition. British Small
Animal Veterinary Association, Quedgeley,
United Kingdom.
