Q, R & S: Pond Keeping Terms – Quarantine to Swim Bladder


Quarantine is the procedure where newly imported or purchased Koi are subjected to a period of isolation. There are two objectives of quarantine:-

1. It is a resting period to reduce stress of newly imported Koi. Irrespective of many of the measures and improvements made in the transportation of koi into the UK, importation is an unavoidably stressful experience for koi. They can experience detrimental changes in water quality while in transit which contribute to stress. Besides affecting a number of key systems in koi, stress has an overall affect on making koi more susceptible to pathogens.

Under these conditions, the low numbers of pathogens which unavoidably and quite naturally travel with koi in a shipment are able to gain a foothold on koi and multiply. One of the objectives of quarantine is to provide such koi with a resting period, where courtesy of an ideal water environment, fish are able to recover from their journey and reduce the multiplication of pathogens by defending themselves. Perhaps upon arrival, koi may be dipped in medication to reduce the overall pathogen load, giving koi a head start. This period is also vital at re-establishing an appetite, encouraging koi to become tame and trusting in their latest surroundings.

2. Quarantine to prevent infestation of existing koi.

All koi will be carrying a pathogen of some description, whether bacteria, virus or parasite. It is wise to monitor a new acquisition, especially where its history is unknown, in a holding facility to see what it is carrying, and whether it is prudent to introduce it to your ‘clean’ collection. Comments such as, “Things have only really deteriorated in my pond since I introduced that Showa 2 months ago”, are quite common, and it is the quarantine that seeks to make it a thing of the past.

Many dealers sell ‘quarantined’ stock, having held them behind the scenes for a period of time but these koi will not necessarily be unstressed and actively feeding. Koi keepers can quarantine all stock themselves in secondary systems. Although these systems are set up for the koi keeper’s interests a quarantine facility must also provide for the koi’s best interests. It is likely that a quarantine system is a budget set-up (being on the small side).

If koi are held in such systems, then it is likely that they will continue to be stressed, especially if held in solitary confinement. Several judgements have to be made that balance the risk of your existing stock, and the health and welfare (and recuperation) of your new acquisition.


A very ingenious device that uses the properties of light passing through a liquid to determine the concentration of a solute in a solvent. The koi keeper can se a refractometer to test the concentration of salt in a pond, very reliably and quickly. There are no moving parts, and its operation does not require any power. Wine producers also use a Refractometer to determine the sugar concentration in grape juice, to judge whether grapes are ready for picking.

Reproduction (see also spawn)

Koi reproduce externally, releasing many thousands of eggs per spawn, that are fertilised by sperm that males release into the water. Koi show very little parental care, being likely to consume their eggs and fry as eagerly as they would any other live food. To ensure that sufficient offspring reach maturity koi produce many thousands of eggs, improving the probability of sufficient numbers reaching maturity. If a koi’s reproductive strategy were to only produce a few off-spring, but tend them with parental care, then the price of koi would be unviable for the hobby to exist.


Respiration is the series of chemical reactions that take place to enable koi to release energy from food. Koi ‘burn’ their digested food aerobically (in the presence of oxygen), to release energy as well as waste products of carbon dioxide and water. The gills are instrumental in respiration as they are the site where the respiratory gasses of oxygen enter and carbon dioxide is released.


The use of common salt, (Sodium chloride), continues to be a topic that koi keepers can discuss at great length.

It is cheap, freely available, easy to use and a relatively non-hazardous compound in the koi keepers medicine cabinet. Depending on the concentration of salt used, it has many applications, some of which are regarded as complementary while others are extreme in their treatment of specific pathogens.

The concentration of the preparation determines the length of time koi are to be treated. These can range from a relatively dilute 0.3% permanent bath, where salt is added to the pond, up to a 3% solution short-term dip or bath to remove external parasites.

Many koi keepers believe that their ponds should carry a 0.3% solution of salt as a preventative tonic and general ‘pick-me-up’, while others strongly maintain that koi are a fresh water fish and should only be subjected to salt during medication.

Once salt has been added to a pond, it can only be removed by water changes (not top ups), and its presence can have a detrimental affect on some plant growth. There is also some evidence that parasites can adapt to different salt concentrations, requiring quite drastic concentrations to eradicate them.

As a short term measure, salting the pond can guard against nitrite toxicity in ponds, but as a complete change of water is required to remove the salt after the crisis, a few carefully carried out 30% water changes would also be effective at reducing the concentration of nitrite (and ammonia and nitrate).

Long term salt treatment to koi in a pond are very effective when confronted with ulcerated koi. The increased salinity reduces osmotic stress on the koi while acting as broad-range antiseptic, cleaning and disinfecting the wound. Salt can be a very misunderstood treatment in koi keeping and its use although easy, can cause complications and constraints in the future.

Sand filter:

Sand filters, or sand-pressure filters are a hi-tech means of mechanical filtration that has been borrowed from swimming pool filtration. Unable to cope with large quantities of solid matter, the sand filter is installed as a final filter to polish water prior to returning it to the pond. Typically bright blue, (but off-white units are also available), this fibreglass pod contains a bed of sand through which water is cleaned.

If too much dirt is allowed to pass through to the pressure filter then it will clog very frequently, requiring a regular back wash through the use of an ingenious multi-valve assembly. Due to the high pressures required for a sand filter to work, a surface-mounted external pump must be used.


Scales in carp are present for protection, and in koi also have an added ornamental interest.

Scales are bony plates whose arrangement allows flexible body movement. Two different types of scale are found on koi, the smaller standard scale of a fully scaled koi, and the larger mirror scales as found on Doitsu fish.

Scales take on the colour of the skin that overlays them, with each one rooted at one end and overlapping the scale behind. Scales continually grow with the size of the fish, and produce growth rings as they develop. The pattern of these rings (wide apart in summer and bunched in winter), can be interpreted to establish the age of a specific koi.


Koi shows are an opportunity to view a selection of top quality koi in a single location. Generally organised by a koi society, district club or even dealer, the koi show event offers the beginner and professional the opportunity to meet fellow enthusiasts, view koi, and purchase stock at some of the most competitive prices. In the UK, a show will be held almost every weekend in the warmer months, and with organisers making increased efforts to provide additional entertainment and items of interest, they can make a full day out for the whole family.

Koi are judged against specific criteria such as size, pattern, skin quality shape etc, and given a score. Koi of similar varieties are judged against each other with prizes for each class and size, besides others such as Best in Show, Best mature, Juvenile koi and so on. Although shows are an opportunity for koi keepers to exhibit their finest specimens, there are koi keepers who would not even contemplate subjecting their prized fish to the journey to and from a show, including a two day period in unfiltered shallow blue vats.


The specific location of the skin of koi in relation to its scales is often misunderstood. Each scale is actually covered in a thin skin which gives it protection, and secretes a mucus layer fro further protection and improved hydrodynamics. When ever a fish loses a scale, the area of skin in which the scale was pocketed is also lost, leaving a localised area open to infection. The scale will not grow back but fortunately the protective skin layer will, restoring any area of lost pigmentation.


Spawning is a koi’s behaviour associated with reproduction. The spawning activities of koi are an extremely physical activity, often being mistaken as an act of aggression. Koi are flock spawners, where several amorous males instinctively drive and chase ripe females, causing them to release thousands of tiny adhesive eggs. Usually taking place in the shallows, seeking a densely planted margin, the males develop a rough texture to their bodies which they use to gain extra purchase on the females.

As the seasons develop from winter through to spring, the female physiology responds to changes in environmental temperature and day length, causing eggs to mature as spawning time approaches. The final trigger is the presence of males that adopt spawning behaviour in response to the pheromones released by the ripe female.

Spawning can last several hours and may prove both exhausting and injurious to female broodstock in particular. Many koi keepers have their koi stripped artificially to prevent the likely injuries associated with rigorous spawning activity.


Stress is the fore-runner of most koi health problems. If stressors can be identified and eradicated, then a health problem is more likely to be avoided. Stress is caused when koi are subjected to a change in their environment which is over and above their natural limits. For example a slight drop in temperature may be quite natural and cause mature koi to spawn, whereas a significant drop in temperature during a water change is likely to stress koi, leading to and increased susceptibility to attack from pathogens.

Koi, like other fish respond to such extreme changes to their environment as a threat, and release a number of hormones to enable them to mobilise energy quickly to allow a rapid fleeing response. Unfortunately, a knock-on effect of these hormones is to reduce the effectiveness of a koi’s immune system. This can prove catastrophic if the stressor, say poor water quality, persists for a lengthy period.

In natural waters, should carp be subjected to an unacceptable stressor (say poor water quality), they have the freedom to move to a less stressful environment. This is not so for koi in a garden pond, and their ‘over reaction’ to prolonged stressors is the stress response koi keepers regularly have to contend with. This is why the behaviour of koi that are stressed is so abnormal, and can be used to gauge the health of koi. No stress, no problems.


A lethal, notifiable viral disease that can attack members of the carp family. Stands for Spring Viraemia of Carp, it is an untreatable condition that can cause widespread mortalities in koi in the spring time. Carp suffering from SVC exhibit quite graphic symptoms of bleeding gills and ulcers and any occurrence must be notified to MAFF immediately. An aquatic equivalent of ‘Foot and Mouth Disease’, sites contaminated with SVC must undergo stringent husbandry and disinfection regimes. Most common in native carp stocks, SVC appeared a number of times in the UK ornamental trade several years ago having been imported from abroad.

Swim bladder:

Koi have a two chambered swim bladder, which is connected to the intestine, just behind the head. The swimbladder is an energy saving structure as it enables koi to achieve neutral buoyancy, where they neither sink nor rise in the water. This allows koi the freedom to remain at a specific depth, without having to ‘swim’ and use energy to maintain its level in the water. Being connected to the gut, the swim bladder is inflated by koi rising to the surface and gulping air into their bladder, swimming downwards until a depth at which they are neutrally buoyant is achieved. buoyant is achieved.

Kill blanketweed and string algae.