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Fish

Fish Medicine at the Avian and Exotic Animal Clinic

The Avian and Exotic Animal Clinic specialises in exotic species and aquatic animals form a significant percentage of our case load. Two of the veterinary surgeons here have done post graduate training in fish medicine. Additionally six of the qualified nurses working at the clinic have had post graduate training in fish and lots of experience with ornamental fish. Naturally we are also prepared with the necessary equipment and always have in stock the drugs commonly used in fish medicine.

Most of the fish we treat are examined at the clinic. However, much can be gained by a site visit, as it allows an observation of the fish in their environment and equally important a direct assessment of the environment. However, the economic realities mean that this is not always possible.

  • Transport to the Surgery
  • Fish Surgery
  • Koi Herpes Virus
  • Laboratory Facilities
  • Autopsy and Specimen Requirements

Transport to the Surgery

This is similar to transporting fish to a show but there are significant differences. Poorly fish will foul their water more quickly so should be transported in more water. Half fill a strong plastic bag with pond or aquarium water, enough for the fish to swim upright and turn around. Then fill with air (enriched with oxygen if available), double bag and place in an insulated box to prevent temperature fluctuation. A cool box or a polystyrene box would be ideal.

A second bag containing an equal volume of pond water, which is also double bagged and insulated should be brought to the clinic to serve as recovery water if the fish is sedated or anaesthetised. It is also often also required for water testing.

Addition of a low dose of an appropriate sedative to the water may help reduce stress but it can influence the findings of a clinical examination and would make external parasites more difficult to find. Therefore, we only recommend this if discussed beforehand on the phone.

Fish Surgery

With improved diagnostic techniques problems that require surgery are increasingly being diagnosed. Most surgical procedures that we perform on fish are minor procedures for example, removing skin cancers, dealing with skin wounds or ocular surgery. We have an increasing number of cases where we perform surgery inside the body cavity. The most common reason is to remove a cancer from inside the body. These cases will have had the cancer identified beforehand to confirm that the surgery can be successful.

As in all other animals, a balanced anaesthetic with an effective pain control plan is essential for success. It has been shown the healing and recovery occurs much quicker when there is good pain control.

Many of the same surgical instruments used for surgery in mammals are also used in fish. Micro surgical techniques and radiosurgery are both invaluable in fish surgery, especially when the operation is inside the body cavity.

During anaesthesia the fish is monitored closely using pulse oximetry and the doppler pencil probe.

Koi Herpes Virus

The virus initially attacks the gills. From there it spreads to the kidneys. Damage to the gills is the most visible sign with high level of deaths. The signs seen can be caused by many different diseases. High numbers of deaths increase the suspicion of KHV while specific testing is required to diagnose the disease (see below).

  • Most commonly seen between June and October when pond water is reaching the required temperatures
  • Infected fish will not develop the disease until the water reaches at least 16 degrees Celsius
  • Survivors are carriers and will pass the infection on to new fish

All suspicious disease outbreaks in carp species (including Koi) should be tested for KHV

Testing for Koi Herpes Virus (KHV)

The most accurate test on dead Koi for KHV is a PCR test.

We will collect the sample free of charge if the fish is delivered to us. However, there is a charge if euthanasia and/or disposal of the body is required. The fish must be chilled and placed in a fridge soon after death (contact us for advice).

Instructions for collecting your own sample

The best sample to collect is a sample from kidney liver and gill on the same swab. This gives the best chance of identifying KHV if it is present.

Live fish sampling

  • From a live diseased fish a gill swab can be used but with just this there will be a percentage of false negatives
  • Open the gill cover to expose the red gill arches inside
  • Insert a sterile swab under the gill cover
  • Roll it across the gill arches until the swab is pink to red with cellular debris
  • Immediately place back in the tube without touching and send it to us

The sample will be ok for several days, but the urgency usually is in diagnosing the problem as soon as possible.

Sampling from a dead diseased fish

  • Aseptically collect kidney, liver spleen and gill (approximately tenth of a teaspoon sized pieces)
  • Place in a sterile sample pot and keep refrigerated and send to us

These are the tissues usually loaded with virus.

Laboratory Facilities

Investigation of the disease problem

The initial important step is history taking. We have developed a history questionnaire which we ask owners to fill in on arrival. This forms the framework for our questions, with some answers giving leads that have to be explored in greater depth.

Evaluation of the aquatic environment is often an essential part of the investigation, this involves analysing the owners water testing records and may necessitate further testing. Temperature and dissolved oxygen levels can only be measured on site.

The fish are examined both in and out of the water. Samples are collected from live fish as dictated by the examination. Some of these have to be tested immediately in the clinic laboratory but some tests need to be carried out in external laboratories.

Radiography is a commonly used to investigate disease problems in individual fish. Contract materials are often given to allow better evaluation. For example, evaluation of the kidneys require an intravenous injection of positive contrast material while for evaluation of the gut appropriate contrast material can be gavaged orally or given rectally. Negative contrast as is commonly used in mammals (i.e. the introduction of air into a body cavity to enhance contrast in the radiograph) is not available for fish due to the resulting disturbance to buoyancy.

Ultrasound and endoscopy are other important clinical tools often used in the investigation of disease diagnostic techniques in fish medicine. Ultrasound can provide information about organ location, size and pathological changes.

Endoscopy allows us to look inside the body and with modern equipment a magnified view is obtained. The mouth, pharynx, gills oesophagus stomach and vent are commonly examined in fish. The body cavity can be entered to examine internal organs and take samples in live fish under anaesthetic through a tiny puncture hole. However in koi as in all the members of the carp family there are limitations of endoscopy. Their well developed pharyngeal teeth limit access to the oesophagus, and examination of the internal organs is severely restricted by the extensive adhesions normally present between their organs and the body wall.

Due to cost constraints CT and MRI are rarely used however if costs come down these techniques would be very useful in some cases.

Autopsy and Specimen Requirements

In a disease outbreak euthanisation of a severely affected individual can provide the information needed to treat the others. Autopsy examinations of any fish dying unexpectedly in a pond is best practice to identify any endemic pathogens present.

As fish start to decompose very quickly, an autopsy examination is most useful when performed on a freshly euthanized fish or within one hour of death. Parasitic disease will not be identified if the fish has been dead in the pond for some time as the internal organs decay rapidly. Live fish for post mortem examinations can be transported chilled to the clinic.

A gross autopsy is the visual examination of all the internal and external structures for abnormalities. It is usually important that samples are collected for diagnostic tests unless the cause is found during the autopsy. Skin scrapes, fin and gill clips should be obtained if not already done. Kidney cultures are routinely collected. Any lesions found should have samples taken for cytology, culture and histology as appropriate. Tissue sampling for histopathology, virus isolation, toxicology, electron microscopy, etc. is collected as required.
Afterwards when the autopsy examination is completed the results are discussed with the owner and further testing of any of the collected samples considered relative to their potential usefulness and to their cost.

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