Parasites and viruses that can harm your Koi

Parasites Visible to the Naked Eye

Lernea, also known as anchor worm, is known to attach itself to the Koi’s skin.  For signs the Lernea parasite is attaching to your Koi, look for what appears to be a small piece of black string coming out of an irritated patch of scales.  Lernea can be simply removed with a pair of tweezers, but make sure to disinfect the area with potassium permangante or iodine.  Lernea can lay hundreds of eggs, which take about two weeks to hatch in the summer.  Like any other parasite, Lernea can also cause a secondary infection like Aeromonas.

Argulus, also known as fish lice or fish louse, is a tiny parasite with a crustacean exoskeleton.  It has two large circular suctions it uses to attach to the Koi’s skin.  Argulus also has a spike that is uses to poke a hole and feed on the Koi’s blood.  Argulus is an egg layer, it can lay several hundred eggs even on solid surfaces like rock.  The eggs have a gestation period of around one month.  Argulus take about one and half months to develop enough to be visible to the naked eye.  During this time, they will attack any fish or amphibians in the pond.  Like any other parasite, Argulus can cause a secondary infection like Aeromonas.  Be careful when holding a larger Argulus as it will use its spike to defend itself

Ichthyophthirius multifilis, also known as white spot disease or Ich, is probably one of the most well known aquatic parasites in the world.  An Ich infestation is easily recognizable by the white spots that appear all over the fish.  The white spots appear very similar to tiny granules of salt peppered all over a Koi.  The name for the white spots is, “Theront.”  When the Theront detaches and sinks to the bottom of a pond or tank, it is called a, “Trophont.”  The Trophont then separates into hundreds of new parasites which are called, “Tomites.”  The Tomites then look for a Koi to attach itself to and repeat the life cycle.  Like any other parasite, Ich can cause a secondary infection like Aeromonas.

Parasites Not Visible to the Naked Eye

Tricodina is a microscopic parasite that is circular in shape.  When viewed under a microscope, it looks similar to a flying saucer.  Koi with a Tricodina infestation usually start “flashing” in order to attempt to remove the source of irritation.  Tricodina are asexual so the form of reproduction they use is called Binary Fission.  Binary Fission is where a single cell divides into two; then the two splits into four and so on.  The best way to remove Tricodina infestations is by adding salt to a pond.  Like any other parasite, Tricondia can cause a secondary infection like Aeromonas.

Trematodes are small parasitic worms also known as Flukes.  The two main Flukes that affect Koi are  Dactylogyrus (Gill Fluke) and Gyrodactylus (skin flukes).  Both types are usually found on the skin or gills. Flukes are not picky about what they eat.  The main difference between the two is that Dactylogyrus is an egg layer and Gyrodactylus is a live bearer.  Dactylogyrus can lay 2000+ eggs within a month in the summer too.  Gyrodactylus can produce up around 2000+ babies a month during the summer.  Flukes survive off the mucus and blood of a fish.  Fluke’s usual lifespan is 2 – 4 weeks in warm water.  However, Fluke’s lifespan can be expanded in cold water.  Like any other parasite, Trematodes can cause a secondary infection like Aeromonas.

Ichthyobodo necatrix, also known as Costia, is a microscopic protozoan parasite.  If left unchecked it can kill a Koi or cause great harm.  Costia is the most difficult parasite to see because it is one of the smallest parasites that attack Koi.  Its life cycle is very short, but it can still remain active in cold water.  To view it, look for a group of swarming commas on the microscope slide.  Like any other parasite, Costia can cause a secondary infection like Aeromonas

Bacteria

Aeromonas hydrophilia, also called ulcer disease or simply, Aeromonas, is the number one killer of Koi.  It does not kill Koi nearly as quickly as a virus like KHV, but if left un-treated, usually a Koi will eventually succumb to the disease.  Aeromonas is always present in water.  It is also an opportunistic bacteria.  Koi will only get infected if something else has harmed them, especially if any part of their slimy coat has been stripped away.  Aeromonas and Pseudomonas usually exhibit similar symptoms.  The ulcer on the skin grows bigger and bigger until muscle tissue is exposed.  After that, the infection turns septic and spreads throughout the Koi’s blood stream.  Next, the kidneys usually fail and then the Koi loses its ability to osmoregulate.  This causes a condition known as pine cone disease, or dropsy.  The Koi will die, usually within two or more the remainder of its bodily functions fail.  Today’s strains of Aeromonas are very resistant to antibiotics.  This is largely due to Koi breaders’ abuse of antibiotics over the years in their attempts to lower mortality rates and increase profit.

Koi can get an Aeromonas infection from:

If a Koi gets an Aeromonas infection, promptly remove it from the pond and immediately put it in a heated hospital tank.  Warm water helps boost a Koi’s immune system and quicken healing.  There are a few options for treatment.  One is Tricide-Neo, which creates holes in the cell wall of Aeromonas, allowing antibiotics to enter and destroy the drug-resistant strains of Aeromonas.  Also, Antibiotic injections can also be used.  If you choose to go the injections route, it’s important to have a licensed veterinarian come to your pond to take a tissue sample and send it in for a susceptibility test.  With the results, antibiotic treatment is like hitting the target with a sharp arrow.  There is no guessing which antibiotic will work the best.  The Koi can be put back into the general population when it has completely healed up.

Pseudomonas fluorescens, also called ulcer disease or simply, Pseudomonas, is less common than Aeromonas.  It does not kill Koi nearly as quickly as a virus like KHV, but if left un-treated, usually a Koi will eventually succumb to the disease.  Pseudomonas is always present in water.  It is also an opportunistic bacteria.  Koi will only get infected if something else has harmed them, especially if any part of their slimy coat has been stripped away.  Pseudomonas  and Aeromonas and usually exhibit similar symptoms.  The ulcer on the skin grows bigger and bigger until muscle tissue is exposed.  After that, the infection turns septic and spreads throughout the Koi’s blood stream.  Next, the kidneys usually fail and then the Koi loses its ability to osmoregulate.  This causes a condition known as pine cone disease, or dropsy.  The Koi will die, usually within two or more the remainder of its bodily functions fail.

Koi can get an Pseudomonas infection from:

  • Stress
  • Abrasive Pond or Tank Surfaces
  • Rough Handling
  • Parasites
  • Poor Water Quality

If a Koi gets a Pseudomonas infection, promptly remove it from the pond and immediately put it in a heated hospital tank.  Warm water helps boost a Koi’s immune system and quicken healing.  There are a few options for treatment.  One is Tricide-Neo, which creates holes in the cell wall of Pseudomonas, allowing antibiotics to enter and destroy the drug-resistant strains of Pseudomonas.  Also, Antibiotic injections can also be used.  If you choose to go the injections route, it’s important to have a licensed veterinarian come to your pond to take a tissue sample and send it in for a susceptibility test.  With the results, antibiotic treatment is like hitting the target with a sharp arrow.  There is no guessing which antibiotic will work the best.  The Koi can be put back into the general population when it has completely healed up.

Koi Viruses

Koi Herpes Virus (KHV) is an extremely infectious disease.  It takes as little as ten minutes of exposure to infect a Koi.  However, the virus can only survive 24 hours without a host.  Goldfish are not susceptible to Koi Herpes Virus.  Koi/Goldfish hybrids are usually also immune.  Koi Herpes Virus (KHV) is also known as Carp Gill Necrosis Virus.  There are two reasons for the different names:

  • Scientists remain uncertain that this virus is a true Herpes Virus (Herpes viruses can lay dormant for years before an outbreak is triggered, usually by immunosuppressant conditions like stress).
  • The virus affects all types of Cyprinus carpio and it is not only limited to Koi.

Spring Viraemia of carp (SVC) is a highly contagious and potentially fatal viral disease that affects fish. As its name implies, SVC can usually be seen in carp during the Spring. However, SVC can also occur in other seasons (like the Fall, especially) and in other species of fish including goldfish and the European wells catfish. The first cases of SVC reported in the United States were in Spring 2002 in cultivated ornamental common carp (Koi) and wild common carp. Until recently, SVC had only been reported in the Middle East and Europe. The number of North American fish species susceptible to SVC is not yet known.

What Species are Susceptible to Spring Viraemia of Carp virus?

The following fish are susceptible to Spring Viraemia: grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molotrix), the common carp (Cyprinus carpio), bighead carp (Aristichthys nobilis), crucian carp (Carassius carassius), tench (Tinca tinca), goldfish (Carassius auratus), and sheatfish (Silurus glanis).  The Cyprinid fish are produced as food fish, ornamental fish (Koi and goldfish) and baitfish.

Signs of SVC in Koi

Some of the first signs of SVC disease in fish might be a change in behavior. A diseased fish might breathe and move more slowly, lay on their side at the bottom of the pond, and form groups in slow-flowing water near the bank of the pond. On the exterior of a fish with SVC, the gills and skin may appear dark red, the belly may be swollen, bloody mucus may hang from the vent, the eyes may bulge outward. The inside of a fish with SVC might contain fluid in the belly cavity and internal organs, blood in the swim bladder, and a gut with reddening and swelling.  It’s important to remember that not all fish showing these signs necessarily have SVC.  These same signs can also be seen in many other diseases. Those fish that don’t die from SVC can recover and appear healthy. These fish may actually still remain infected with the SVC virus and continue to spread the virus to other fish. For this reasons the disease is difficult to eliminate from a site. The best way to confirm diagnosis of the SVC virus in fish is through virus isolation and other sophisticated diagnostic tests performed by an approved laboratory.

SVC Spread and Control

The spread of SVC occurs a number of ways.  It can spread through contact with water contaminated with the infected fish’s feces, urine, or mucus. The virus can also spread through contaminated equipment, predatory birds, fish parasites, and via the outside of an infected fish’s eggs. Once SVC is established at a site, it may be difficult to eradicate because of virus-infected carrier fish. It may be necessary to destroy all aquatic life in a pond to eliminate the disease from the site.

Although complete eradication is very difficult, SVC can usually be contained and/or controlled within high-risk zones through better management practices, including strict biosecurity procedures via surveillance. People can transmit the virus along with them as they move from place to place.  It is transmitted via their footwear, clothing, equipment, and other things they come in contact with. The virus however, does not cause disease in humans. There have been no reports of humans being infected with the SVC virus from contact or from eating an infected fish.

SVC Prevention Information for Hobbyists and Koi Keepers

Koi keepers and hobbyists who actively transport and show their fish in any type of organized competitive Koi shows should always show their fish in a way that keeps each participant’s Koi in separate show tanks.

The best way to prevent an outbreak of SVC in a pond is to quarantine fish from any unsecured sources.  Quarantine should be done at 75 degrees and for a minimum period of three weeks Fahrenheit before they can be released into the general population.