Koi Disease Diagnosis and Treatment

koi diseases

Every fish owner deals with sick fish.  Seeing the issues early is the difference between life and death and key to ensuring that your precious Koi carp have a happy and stress-free life.

Warning signs

The body language of your fish can be the first indication of any problems. A Koi that is feeling unwell is likely to leave the shoal and hang around on its own. The first signs of a problem are often when a Koi has one or more fins held tight to the body with the dorsal fin also held down. The fish might also start breathing heavily – this can be hard to see as it can be mistaken for chewing, so fish must be observed when they aren’t being fed. The fish might tend to sit on the bottom, again with its fins in – this is a sign of stress. If it sits on the bottom with its fins out it could be a swimbladder problem or due to cold water temperatures.

Koi Disease Diagnosis and Treatment

Although Koi are cold water fish, if the water is too cold it can have detrimental effects on your stock.  Flicking and flashing are signs of external parasites; the fish might also shake its pectoral or pelvic fins or twitch its dorsal fin in irritation.

Taking a skin scrape

At the first sign of any irritation you should take a skin scrape immediately to identify any external parasite. Excess mucus production, or a velvet sheen to the skin, is a sign that things have gone a little bit too far and that treatment is urgently required. If you have taken several scrapes and have observed no parasites then the problem could be environmental, such as poor water quality, or due to untreated or contaminated tap water entering the pond. It could also mean that there is a more serious problem which could be bacterial or viral.

The signs would be fraying of the fins, open sores or bruising, reddening of the skin and visible blood vessels, raised scales and bulging eyes. The gills could be pale and anaemic or have the appearance of being eaten away. In this instance, and assuming that poor water quality is not the cause, it is very important to get veterinary assistance to identify whether the cause is bacterial or viral. Bacterial infections can be treated with antibiotics and are a symptom of poor water quality and poor husbandry, either in your system or in the one that the fish came from.

Viral infections such as Spring Viraemia of Carp (SVC) and KHV cannot be cured and have to be confirmed by a laboratory test. Viral diseases are due to an infection from fish-to-fish contact and are not caused by environmental conditions as bacterial infections are. Observation is vital – five minutes of monitoring at feeding time only is not sufficient – and aeration must also be sited in such a way that observation can be easily carried out. Just because a cold water fish comes up for food, it doesn’t mean it is a healthy fish.

Disease issues

Diseases are either caused by poor water quality, parasites, bacteria or viruses. Assuming your water quality is good, and your filtration is well maintained, the first thing to look for is a parasite infestation, which you can identify by taking a skin scrape and looking at it under a microscope.

The most common forms of parasites that affect Koi are Costia, Trichodina, whitespot and skin or gill flukes; there are others but they are less common. A microscope and a good Koi health book, such as Duncan Griffith’s book Step by Step Advanced Koi Diagnosis and Treatments, will help you to diagnose which parasite is causing the problem and how to treat it.

Top 10 Quarantine Tips

  1. Wear waterproof gloves when you’re handling Koi in a quarantine setup to prevent
    any disease or organism from entering or leaving the quarantine facility.
  2. Ensure that you maintain a clean environment in and around the quarantine system.
  3. Observe your fish regularly, other than at feeding time.
  4. Maintain and monitor filtration and water quality regularly.
  5. Carry out regular water changes.
  6. Ensure immediate and effective treatment of any health problems that you observe while your Koi are in quarantine.
  7. Only treat once a problem has been identified and don’t be tempted to interfere with your fish if there isn’t a problem.
  8. Ensure that temperature ramping is carried out correctly.
  9. Don’t overfeed the fish in the quarantine setup before the filter is mature enough to cope with the increase in fish and food waste products.
  10. Maintain biosecurity at all times – your hands and any equipment you use must not come into contact with any other pond and vice versa.

Jargon Buster

Koi Herpes Virus gillsKoi Herpes Virus (KHV) is a form of herpes virus that affects carp (including Koi). Mortality rates during an outbreak are 80-10%. Once infected, any surviving fish are likely to become carriers and can re-develop the disease at any point in the future, thereby infecting other fish they come into contact with. There are plans to make KHV a notifiable disease in the near future.

Temperature ramping is the rapid raising of water temperature in an effort to bring on an outbreak of KHV.

Askin scrape is when a sample of mucus is taken from the body of a Koi for examination under a microscope in order to identify external parasites. Spring Viraemia of Carp (SVC) is a rhabdovirus that affects several species of fish including carp and Koi. Mortality is 5-100% and any survivors then become carriers. This disease has been Notifiable for some years now, which means there is a legal obligation to notify the authorities if an outbreak is confirmed. There are strict controls on the import of fish from countries where SVC is found which means that outbreaks of this disease within the UK are very rare.

Stressed Out

Koi are highly susceptible to the effects of stress. Stress can be brought on when moving Koi, both during transport and when they are introduced to a new environment. When a Koi is stressed the automatic nervous system releases adrenaline into the blood stream. This increases the heart rate, which also increases blood pressure, breathing and metabolism.

Continued handling prolongs the exposure to stress and can lead to the suppression of the immune system and susceptibility to disease On the other hand, it is important, since the discovery of KH\, that fish are exposed to controlled stress (temperature ramping) during the quarantine process since the KHV virus only shows itself when the water temperature is 18-27°C.

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