Koi health introduction

There are few hobbyists who have not experienced some health problem with their Koi, whether a minor hitch or a serious disease. Many Koi health problems can be related to environmental or management issues, which lead to outbreaks of disease, so it is important to ascertain what caused the problem and how to treat it.

There is an old adage that Koi keepers are water keepers and water quality is essential to Koi health, but the other big factor is stocking density. Too many Koi leads to stress through overcrowding and competition for resources, notably dissolved oxygen in the summer. We should also bear in mind that introducing new Koi carries the risk of a disease outbreak.

Many Koi keepers consider spring to be the hardest time of year, with its fluctuating temperatures and recovery from winter. Some will treat their pond to prevent outbreaks of disease, which is not really sound management. In fact, to ensure healthy Koi in the spring, you must carry out good preparation for winter and spring during the preceding summer. Make sure that water quality is satisfactory, including dissolved oxygen, and feed with a good quality diet. Koi entering the winter months in a healthy condition do not experience disease outbreaks in spring.

In the summer, the best way to monitor your Koi is to spend time watching them – when the water is warm (above 16°C), they should be active and feed readily. In winter when the water is cold, Koi tend to spend time on the bottom of the pond, huddled together and moving occasionally. Observing Koi is the best management tool we have and the least invasive – it is possible to catch a Koi and examine its mucus for parasites but it’s best to net and handle them as little as possible.

A small ‘first aid’ kit is handy to treat any minor injuries or infections on your Koi, including tweezers, cotton buds and a topical antiseptic treatment. Only intervene if it is really necessary because sometimes treating a Koi can make a wound or infection worse. If a Koi becomes sick or one dies, test the water for everything possible – dissolved oxygen, ammonia, nitrite, pH and temperature – to eliminate environment as a cause. If the water quality is satisfactory, it is worth netting a Koi and taking a sample of mucus to check for parasites, but bear in mind that a sick fish tends to get infected with parasites and these may be a secondary problem. If there’s no problem with the water or Koi but the ailment continues, seek professional advice.

A common cause of disease in Koi is stress, and stressed Koi are more easily stressed. The journey from Japan is immensely stressful for Koi and it can take several months before they fully recover. To reduce stress, make sure the pond is well aerated, that the dissolved oxygen concentration exceeds 7mg per litre, and add a small amount of pond or cooking salt to the water.

Written by Bernice Brewster

Anatomy of a Koi fish

A basic understanding of Koi anatomy is useful for any hobbyist. Notable external features are the barbels for tasting, nostrils for detecting dissolved chemicals in the water, scales, gills and fins. Along the mid-line of the body are scales with pits in them, known as the lateral line, which is a sense organ that can detect changes in pressure. It is unusual to find any disease or disorders here.

The scales are bony protective plates, beneath a layer of living skin – this skin produces special proteins and enzymes, released into a thin layer of mucus that lubricates the fish and helps to repel bacteria, viruses and parasites. Parasitic skin infections are common, causing the Koi to become grey (from excess mucus) and irritable, flicking and rubbing repeatedly. Carp pox is caused by a herpes virus and infects the Koi’s skin, producing a waxy white lump. Finally, the bacterium ‘atypical Aeromonas salmonicida’ can infect the skin and lead to outbreaks of ulcer disease.

Inside the Koi is a gas-filled sac, known as the ‘swimbladder’, which acts as a buoyancy organ so Koi can stay at any depth with the minimum use of energy. Koi can control the gases inside it, with gas added or removed by blood vessels running over the surface of it. There is also a thin tube to the Koi’s throat so they can add gas by gulping air – Koi recently imported from Japan will often do this.

There are various conditions that can affect the swimbladder, from fungus to filling with fluid. The symptoms are similar: the Koi swims with a distinct rowing action and rises to the surface often to gulp air. When resting, the Koi are found on the pond bottom with the pectoral fins extended. Unfortunately, it is very difficult to determine what disease is affecting the swimbladder and so offer any treatment. Fluid can be removed, but without knowing why this has happened or how to control it, the swimbladder will fill with fluid again very quickly.

Koi breathe using gills with finger-like filaments. Blood is in contact with the water, allowing the gas exchange of oxygen and carbon dioxide. The most common infection is gill fluke, which is usually a secondary problem – where large numbers of Koi suffer with this parasite, it suggests they are stressed. If the stressor is removed, Koi can usually control the gill flukes. Other parasites, notably white spot, can damage the gills and allow bacteria and fungus to lead to further disease.

In recent years, Koi Herpes Virus (KHV) has been responsible for many Koi mortalities. This viral disease spreads rapidly when introduced to the pond and a characteristic symptom is erosion of the gill tissue. Eventually, the gills are exposed to the environment and usually respond by producing more mucus and then by cell proliferation, leading to a condition popularly known as ‘clubbed gills’.

Written by Bernice Brewster

Photo courtesy of The Environment Agency

What causes Koi health problems

Poor water quality causes more Koi diseases than any true fish disease. Koi rarely die from a pollutant introduced to the pond, the problem is usually related to filtration or dissolved oxygen. So the most important aspect of water management is monitoring water quality.

Koi produce nitrogenous waste in the form of ammonia, normally broken down by a pond’s filtration system into nitrite and then nitrate, through the action of bacteria and other micro-organisms. Ammonia and nitrite are poisonous and will make Koi ill if they accumulate in the water.

When dissolved in water, ammonia exists in two forms, free and ionised. Free ammonia is most poisonous and becomes increasingly harmful with increasing water temperatures and an alkaline pH (pH7 and above). Ammonia affects the gill tissue, causing filaments to fuse together or become clubbed, and reduces the ability of the blood to absorb oxygen from the water. Lastly, ammonia is a neurotoxin, which means it will poison the Koi’s nervous system. Ammonia is a common pollutant of new ponds, where the biological filters have insufficient bacteria to break it down.

Nitrite causes a condition known as ‘brown blood disease’. The nitrite binds to the red pigment in the blood, preventing it from absorbing oxygen from the water – an effect similar to carbon monoxide poisoning in humans. Nitrite also affects the blood vessels and heart, causing them to relax and eventually collapse.

If the pond becomes polluted with ammonia or nitrite, increase the aeration to help gas off these pollutants. Undertake regular partial water changes to dilute the ammonia or nitrite, reducing the frequency as pollutants decrease. Always use a water purifier or treatment to dechlorinate the incoming tap water.

Cold-blooded Koi are also dependent on water to regulate their body temperature and metabolism. In summer when the water is warm, Koi are active, body functions such as digestion, reproduction and the immune system are at their peak. As the water temperature drops in autumn and winter, Koi don’t breed, feeding declines and the immune system ceases to work. Once the temperature increases in spring, the immune system fires up again.

Koi will do their best to survive any pollution incident but without oxygen they will die quickly, so regularly measure the pond’s dissolved oxygen concentration. Until recently, the recommended minimum concentration was 6mgl but this has been raised to 7mgl for healthy growth, tissue repair and reproduction.

Don’t assume that if oxygen levels in the pond drop, Koi will be seen gasping at the surface – in reality, at this stage the Koi are minutes from dying. The first sign of low oxygen is when Koi, who should be actively swimming and feeding, behave as though it is winter, lying on the pond bottom, neither feeding nor swimming. You should immediately increase aeration to the pond – in an emergency, a pump can be placed in the pond and allowed to splash water over the pond surface. In the long term, consider installing an air pump.

Written by Bernice Brewster

Parasitic diseases

Although it is perfectly possible to have a parasite-free pond, there is always a risk of parasites being accidentally brought in with new fish or their transport water.

Common Koi parasites are those that attach to the body surfaces (skin, gills and so on). These include various protozoa (single-celled organisms) and worm-like flukes. Virtually all these skin-dwelling parasites are invisible to the naked eye.

 Other Koi parasites include tapeworms (inhabiting the fish’s gut or body cavity), thread-like nematode worms (in the gut), and parasitic crustaceans, such as the disc-shaped fish louse (temporarily attaching to skin).

Often, the first sign of a looming protozoa or fluke problem is when one or more Koi repeatedly rub their flanks against submerged objects, or leap from the water. These symptoms can also arise from a water problem (such as high nitrite level) so always carry out water tests before considering parasites as the cause.

Commercial liquid remedies are available for treating common skin and gill parasites – these treatments are added directly to the water so you will need to know the volume of your pond in order to administer the correct dosage. Prompt treatment is important because many skin and gill parasites are highly infectious and potentially lethal. If parasite problems persist then consider having your Koi checked by a fish health specialist (ask your Koi dealer) – this should reveal which type of parasite is to blame, enabling the most effective treatment to be selected.

The risks of introducing parasites into the pond can be greatly reduced by obtaining Koi from a reputable dealer who practices good husbandry and proper quarantine procedures – try to get a recommendation from an experienced Koi keeper.
 

Written by Dr Peter Burgess

Photo courtesy of The Environment Agency

Bacterial, viral and fungal diseases

Bacterial diseases
Common bacterial diseases in Koi include fin-rot and mouth-rot, which cause the affected tissues to erode, often accompanied by localised whitening or reddening. Other bacteria cause ulcers, manifesting as crater-like sores on the skin. A bloating condition known as ‘dropsy’, in which the Koi’s belly region swells and the scales stick out, can also have a bacterial origin.

Mild bacterial infections can be treated using a commercial remedy (such as fin-rot remedy or ulcer remedy), added to the water. Serious or persistent cases (including dropsy) may require antibiotics from a vet (your Koi dealer may be able to recommend local vets who deal with fish). Many bacterial problems are triggered or aggravated by unhygienic water conditions or overcrowding, so good Koi husbandry is the best prevention.

Viral diseases
A relatively common viral disease of Koi is ‘carp pox’, which causes whitish wax-like growths on the skin and/or fins. Fortunately, this virus is more disfiguring than harmful and eventually the growths should disappear of their own accord. There are no treatments for viral diseases of Koi. The provision of clean water conditions and optimal nutrition will help the Koi’s immune system to overpower many viral problems.

Fungal diseases
Fungal infections manifest as one or more white-grey fluffy growths that stick out from the Koi’s body surface. These fungal masses may resemble tufts of cotton wool. They are not highly contagious and generally only a single Koi is affected. Use a commercial fungus remedy or salt treatment. If you have a spare pond or other suitable temporary housing system, you can treat the affected Koi in isolation.

Generally, it is only stressed or injured Koi that succumb to fungus attack, so always investigate for any underlying causes (such as damage to the Koi’s skin) if a fungus problem occurs.

Written by Dr Peter Burgess

Photo courtesy of The Environment Agency
 

Netting and bowling a Koi

There will be occasions when it is necessary to catch and move your Koi. Most often this will be to treat a health problem when you may want to remove your Koi from your pond for inspection or to apply a topical treatment. You may also need to move your Koi from a pond to a quarantine system. Catching and moving Koi are stressful procedures so it’s important that you do it right. If you’re unsure, always seek the advice of a professional. When you catch Koi you should always place them in a viewing bowl.

Step one: Net at the ready
Before attempting to catch any of your Koi,
ensure that your net and bowl are of a suitable size for the Koi you intend to catch. Then, when you’re ready to catch the Koi, turn off all the aeration so that you can see what you’re doing; this will help reduce the risk of knocking and damaging any of your Koi as you chase them around the pond.

Step two: Bowl in place
If you don’t have anybody on hand to help, place the bowl in the pond and fill one third of it with water. If you have someone to help you, keep the bowl out of the pond until you’ve caught the Koi – your helper can then actually use the bowl to help you manoeuvre the Koi.

Step three: Gently does it
Use your net to catch the Koi – be gentle as the trick here is to use the net as more of a guide to bring the Koi to the surface. Once you have the Koi at the surface, keep the net below the water level as you bring it towards your bowl so the Koi does not become entangled in the net.

Step four: Going solo
If you’re working alone, bring the net over to the bowl, which should already be in the pond. Then, using the edge of the net, bring this out of the water so that it rests on the side of the bowl. Then, gently put pressure on this side of the net so the bowl tips on its side. When this side of the bowl is below water you can tip the net, which will cause the Koi to swim from the net into the bowl.

Step five: If you have help
If you have help, once you’ve netted the Koi get the bowl and place it in the pond at an angle to the net. Then, as the bowl starts to fill with water, turn the net towards the bowl; the Koi will swim from the net into the bowl.

Written by Keith Holmes

Photos courtesy of Keith Holmes

Using a sock net

Sock nets are shaped like a table tennis bat with a long, open-ended, sock-like net trailing behind them. Like bowls and nets, they are available in various sizes so you should always find one that is of a large enough diameter and length for the largest fish in your pond. Once you’ve moved a Koi from your pond into a bowl using a net you should never use a net if you need to move the Koi again – you should always use a sock net. This will ensure that you do not cause your Koi any unnecessary stress or damage.

Step one: Net and bowl first
Sock nets are useful ways of moving Koi quickly and safely over short distances. Before using a sock net you will need to catch the Koi you want to move and place it in a suitable bowl – use the technique on the opposite page.

Step two: Wet your sock
It’s important that you choose a sock net of a suitable diameter for the Koi you intend to move. Once you’ve got your net to hand, submerge it in your pond and pull it through the water to make sure that it is wet before use.

Step three: Head first
Take hold of the handle of the wet sock net with one hand while you hold the end of the sock net with your other hand. Once you’re comfortable, place the sock net into the bowl vertically and coax the Koi into the sock net head first.

Step four: Keep it straight
Once the Koi is in the sock net you can lift it from the water. Make sure you keep the sock net as straight as possible – you can do this by using one hand to hold each end of the sock net. You should keep the sock net in this position while you move the Koi.

Step five: Framed end first
Once you’ve moved the Koi you’re ready to release it from the sock net. To do this, place the sock net in the pond then remove the framed end from the pond slowly. The Koi will swim out of the end of the sock net into its new home.

Written by Keith Holmes

Photos courtesy of Keith Holmes

Bagging a Koi

When you transport Koi, for example from your dealer to your pond, you should also use a plastic bag – and plastic bags are also ideal for inspecting Koi. It’s important that you use the correct technique for this process to ensure that it is as stress-free as possible for your Koi.

Step one: Double bagging
Firstly, you will need to catch and bowl the Koi you want to bag. You will also need to make sure that you have a bag of a suitable size, elastic bands and air or oxygen to inflate the bag to hand. Once you’ve bowled the Koi, take one plastic bag and fill it with a small amount of water. Then, place this bag inside another bag. This is called double bagging and is basically a safeguard in case one bag leaks.

Step two: Prevent leaking
When you’ve created the double bag, roll the tops of the bags down to prevent water getting in between the two. Then, take hold of the bag at each side and place it into the bowl – gently follow the Koi until it swims into the bag. 

Step three: Enough water
Once the Koi is in the bag, check how much water the bag contains. If you’re transporting small Koi, a third of the bag should be filled with water. For larger Koi ensure that there is enough water to cover the Koi. Keeping this in mind, add or remove water until you have a suitable amount.

Step four: Fill with air
You can now lift the bag out of the pond and lie it flat ready for oxygenation. Unroll the top of the bag and remove any air by gently pushing on the bag to expel it. You can now fill the bag with air from an air pump or oxygen cylinder. The aim here is to try and get as much air into the bag as possible.

Step five: Seal with bands
Once the bag is inflated with air or oxygen, you need to secure it using elastic bands. Each bag should be sealed individually and it is a good idea to use two or three bands on each one, just in case any of the bands split in transit.

Written by Keith Holmes

Photos courtesy of Keith Holmes
 

Transporting a Koi

Box size, length of journey and temperature are all very important considerations when transporting Koi.

Step one: Go rectangular
Once your Koi is bagged you will need a suitable box for transportation. Ideally, you should source this before you start bagging your Koi – your local Koi dealer may be able to help. Ensure that the box is strong enough for the weight of the bag – you might need to add extra tape for additional strength. Place the bag in the box so that it lies flat and avoid standing the bag up – a long rectangular box is better for moving Koi then a tall square box.

Step two: Fill any gaps
Once you’ve placed the bag in the box, fill any spaces with newspaper or bubble wrap or inflate a small bag and place it in any gaps. This will help prevent the bag from moving in transit.

Step three: Reinforcement
If you have a spare piece of cardboard it is a good idea to place this over the top of the box before you seal it to offer some extra protection and strength. You can do the same on the bottom of the box before you place the bag inside.

Step four: Seal it shut
You can now seal the box by folding the corners under each other or by using tape, which is advised for longer journeys. The box can then be loaded into your car ready for transportation.

Step five: Sideways on
When you put the box in your car, place it so that the longest side of the box goes from one side of the car to the other. Don’t place the box head on because if you brake suddenly the Koi will smash into the front of the box. By placing the box sideways on the Koi will roll in the bag and this will reduce the risk of injury.

Written by Keith Holmes

Photos courtesy of Keith Holmes

Handling a Koi

Every Koi keeper will need to inspect their Koi for signs of damage and disease at one time or another. A confident Koi keeper can undertake this task easily, although if you’re unsure it is always recommended that you seek the advice of a professional. If you are a confident handler you can check a Koi in a bowl and lift it out of the water so that you can inspect the mouth and other areas in more detail – it’s best to use a plastic bag if you’re inexperienced.

Step one: Gentle but firm
Once you have bowled the Koi you want to inspect, use both hands to pull the Koi to the side of the bowl and hold it with a gentle but firm grip. If you are not familiar with this procedure, contact a health professional or vet as it could cause undue stress to your Koi.

Step two: Turn the Koi over
When you’ve gently pulled the Koi to the side of the bowl you can inspect its underside for damage and apply any topical treatment required. Then, once you’re happy, simply let go of the Koi and it will correct its position and return to normal.

Step three: Open wide
You may also want to look at your Koi’s mouth. If you are confident you can do this by lifting the Koi from the bowl – place one hand under its head and the other hand towards the back. Don’t grip the Koi too tightly.

Step four: Move with your Koi
When you’re happy with your grip you can lift the Koi from the bowl. Naturally, the Koi will flap from side to side – the trick here is to let your hands move with the Koi. Do not try and grab or stop the Koi, simply allow your hands to move with the movement of the Koi. If you have any doubts about handling your Koi, ask for help from a qualified health specialist or use a plastic bag – follow the steps for bagging a Koi on page 82.

Step five: Take a closer look
The Koi will eventually stop moving – you can then lift it to view its mouth area and any other areas that you want to check. If you are very confident you can also use this method to move Koi. When you’ve finished your inspection you can place the Koi back in the bowl or pond.
 

Written by Keith Holmes

Photos courtesy of Keith Holmes

Taking a skin scrape

Whenever you suspect a parasite problem it is advisable to take a skin scrape that can then be examined under a microscope. If you remove your Koi from the pond for a general health check, try and carry out the skin scrape at the same time so that you don’t subject your Koi to any unnecessary stress. If you don’t have a microscope to hand your Koi dealer may be able to help you out, although you must view the scrape quickly, ideally within 30–60 minutes. In most instances it is easier to take a skin scrape if you have someone to help you, so enlist the help of someone before you start. If you’re not experienced at taking skin scrapes you should choose a suitably qualified Koi health professional. You should also ensure that you have all the necessary equipment to hand.

Step one: Preparation
In most instances it is easier to take a skin scrape if you have someone to help you, so enlist the help of someone before you start. If you’re not experienced at taking skin scrapes you should choose a suitably qualified Koi health professional. You should also ensure that you have all the necessary equipment to hand.

Step two: Raise the Koi
Once the Koi has been bowled, follow the steps listed on the opposite page for viewing the underside of a Koi – get the Koi against the side of the bowl but don’t turn it upside down. In order to take a scrape the Koi will need to be raised against the side of the bowl so the area you want to scrape is above the water level.

Step three: Head to tail
With the Koi in this position, take your blunt instrument (wooden spatula or similar) and run it from head to tail along the Koi in the area from which you want to take the sample.

Step four: Transfer mucus
Once you have collected some mucus from your Koi you can then let go of the Koi and transfer the collected mucus onto a microscope slide ready for examination.

Step five: Swabbing
If you want to take a swab from an open wound or ulcer you can do this in a similar way, but the Koi may need to be turned upside down or actually lifted completely from the bowl. You will need to get a swab from your local health professional or vet and get it back to them or in the post to a laboratory as soon as you can after carrying out the procedure.

Written by Keith Holmes

Photos courtesy of Keith Holmes

Treating and dosing

If your Koi fall ill it’s important to use the right treatments in the right doses – so, with the help of our resident health expert Bernice Brewster, we’ve compiled a comprehensive guide to common ailments and their treatments.

When your Koi are ill it can be a worrying time and you will want to do all that you can to make them better as soon as possible. Common diseases can be identified by every Koi keeper, although diagnosis of many parasite infections requires the examination of mucus samples using a microscope as it is important to accurately identify any disease in order to apply the correct treatment.

Treatments are most effective when applied to the whole pond and tend to be most active during the first four hours after they’ve been added to a pond. It is good practice to follow up any pond treatment with partial water changes on subsequent days to remove any residue from the medication. You must always be careful when adding any medication to a pond and take great care to weigh or measure the treatments accurately.

Example
To work out the treatment for whitespot for a 4,400-gallon pond (20,000l):

• The treatment for whitespot is malachite green and the dosage rate is 0.1mgl of pond water
• To work out the treatment you first need to multiply the pond volume by the dosage rate and then you have to divide it by 1,000 because 1,000mg are
  equivalent to 1g
• Our pond is 20,000l so: 20,000 x 0.1 = 2,000mg. 2,000 ÷ 1,000 = 2g

Top treatment tips

• Stay by the pond for at least 20 minutes following the addition of any treatment and watch the Koi for signs of distress. If they become distressed, start water changes immediately.
• Always treat the pond when you are able to monitor the Koi often (every 10–20
  minutes). You will then be able to start immediate water changes if necessary.
• Always read and follow the manufacturer’s instructions to the letter.
• Never add extra treatment for good measure. Many treatments are poisonous and there is a fine line between a correct dose and an overdose. If in any doubt, seek advice.
• Please remember that many factors, including water chemistry, temperature, age and condition of the fish can alter the efficacy of any treatment. No responsibility can therefore be accepted for the use of these figures or any losses incurred.

Written by Bernice Brewster