P: Pond Keepers A to Z – Parasites to Pond Pumps


Just as a predator attacks and eats its prey, and a scavenger lives off dead organic matter, a parasite needs another animal on which to live.

The relationship between parasite and host is quite a natural one, with a balance being maintained between the host and the parasite where the parasite populations are kept to a minimum. In fact, it is in the parasites best interests to keep its host alive, as killing it would mean having to find a new host on which to feed. Parasites are like any other pathogenic organisms in that they proliferate when its host’s immune defences are reduced. As this happens when koi are stressed, it is not surprising for parasitic infections get out of hand during poor or unstable water conditions.

In koi keeping, many parasites use koi as a their host, either for their whole life or merely as a part-time benefactor. Parasites can be classified by their size, their life cycle and even whereabouts on a koi they take up residence.

Protozoan parasites are microscopic, and very simple in structure. These include Trichodina, Chilodinella and Costia all of which can only be positively identified in a mucus scrape when viewed under a microscope. These relatively simple organisms can be routinely controlled by dosing a pond with formalin and malachite based pond treatments. The larger, metazoa are generally visible to the naked eye and include anchor worm, fish lice and leeches. These are more difficult to successfully treat, and action such as salt baths or hazardous organophosphate treatments may be the only answer.

Those parasites described so far are all ectoparasites, living externally to the fish and consequently are more commonly identified and treated. Less well known, and usually more chronic in their effect on a host koi are endoparasites (those that live internally). These include parasites that live in the gut, other internal organs and even the eye. Because of their location on a host, endoparasites are more difficult to diagnose and also quite a challenge to treat.


A pathogen is a disease-causing organism. They can range from an incredibly microscopic virus through to a tapeworm several centimetres long. Koi interact with bacteria that are pathogenic and non-pathogenic. For example, pathogenic bacteria include those that cause fin-rot and ulcers while non-pathogenic bacteria are those colonies of bacteria involved in the breakdown of wastes in a biofilter.


pH is a measure of the acidity or alkalinity of a substance. The pH scale runs from 0 to 14, with 7 being neutral, and figures below 7 acidic, but above 7 alkaline. In koi keeping, it is a useful guide to the suitability of pond water for koi and it will affect all aquatic life including koi and filter bacteria. Koi can accommodate a pH ranging from 7.0 – 9.0, with the emphasis on it being stable. The closer it approaches 7, which is neutral, the harder it is to remain alkaline.

More chemically speaking, pH is a measure of the free Hydrogen ions in the water. The more H+ ions, the more acidic water becomes. The natural tendency through biological processes such as biofiltration and respiration is for water to become more acidic, just what koi and other aquatic life do not want!

Fortunately, the pH can be stabilised by adding a pH buffer which ‘mops’ up free hydrogen ions, maintaining a stable pH. Typical pH buffers which maintain stable and healthy pH include calcium carbonate which can be added to the filter in a net-bag in the form of lime chippings, crushed shell or even tufa rock.

Pharyngeal teeth.

The pharyngeal teeth (located in the pharynx or throat area) are the koi’s chewing mechanism. They are a common feature to many fish in the carp family. Perhaps more accurately described as a grinding mill, the pharyngeal teeth fragment any food passing from the mouth into the gut. This can often be seen as a ‘chomping’ action when koi move their jaw in an exaggerated and repeated way. By breaking the food down into smaller particles, it is prepared for more efficient enzyme attack prior to entering the intestine.


This is a dual purpose oily liquid which, depending on the concentration used, will determine what its effect on koi will be.

- Phenoxyethanol as an antibacterial treatment.

Added to the pond water at a rate of 100mg per litre (0.01% solution) it will be effective against finrot and mouth fungus.

- Phenoxyethanol as an anaesthetic.

Add to a bowl of pond water at a rate of 1ml per litre (0.1%) and it will sedate koi in order to carry out topical treatment or to dress wounds. Anaesthetised koi should always show opercula movement, and can be resuscitated by holding the koi in a flow of fresh pond water.


Koi, like all fish are poikilothermic in that their body temperature varies according to the water temperature. As the pond temperatures warm up, so does the body temperature of koi with a knock-on effect to their metabolism. This is in contrast to mammals, which irrespective of their surroundings (excluding life-threatening extremities) are able to maintain a constant body temperature, removing the constraints that geography and the seasons may have on their lifestyle. It is as a result of koi being poikilothermic that it is better practise to feed lower protein diets in spring and autumn. This practice would not be necessary if koi were endothermic and able to maintain a constant body temperature, irrespective of their environment. If this were the case, then koi could be fed a growth diet all year round.


The koi pond is the common denominator in koi keeping, for every koi keeper must have one. Put simply, a koi pond is a body of recirculating water, retained within a water-tight boundary but that is where similarities between koi ponds end. Much emphasis is put on the design of a koi pond and the materials used with the overall objective of providing as optimum a pond environment as possible for the koi, with ease of maintenance and good viewing for the koi keeper.

During the planning, decisions such as pond size and position must be made, which may have an overall impact on a pond’s style whether informal or formal. Materials used for its construction and design of its filter are additional factors which must be planned and incorporated into an overall budget prior to installing and constructing a pond.

Pond design for the farming of koi is completely different from that of keeping koi, as emphasis is on koi health and growth. Production ponds are traditionally excavated out of clay and made turbid by the koi rooting around on the pond bottom. Koi paradise without a filter in sight! Food for thought when considering the perfect pond design?


A fish complaint that is quite common in koi and other pond fish, causing the eyes to bulge out of the head. Caused by a range of agents or factors, the symptoms are more accurately described as exophthalmia – see Encyclopaedia KPG Feb. 2000.


A post-mortem is a procedure carried out on a koi that has died for no apparent reason. One cannot be carried out satisfactorily without significant skill or experience or the necessary back up of diagnostic facilities such as a field laboratory and bacterial culture facilities. A post-mortem is usually an after thought having experienced a sudden koi mortality and as a consequence is usually impractical for an effective examination to be carried out. To be of any use, a koi must be examined no later than 1 hour (at the most) after death. Koi that have been preserved in refrigerators or freezers cannot provide sufficient information as to the causes of death through the deterioration of body tissue and pathogens while in storage.

If a fish is examined in a fresh state, then bacterial swabs are taken both externally and internally and cultured on agar plates for the identification of causative bacteria. This is further complicated by the fact that the presence of bacteria in a culture is not an indication of an infection but is a likely occurrence on a swab taken from any non-sterile subject such as a koi. Bacterial cultures require intensive investigation and staining to identify the specific nature of the bacteria.

The colour and appearance of key tissues such as the gills, skin and internal organs such as the spleen and liver are examined under the microscope for any signs of abnormality.

Rarely is there evidence that points to a single cause of death, but a number of clues may suggest that the cause of death is likely to have been any one or combination of a number of specific agents.

Potassium permanganate

A widely used chemical with an unmistakable deep purple colouration. Supplied as a crystal, potassium permanganate is dissolved in water and traditionally used as a dip against external parasites and bacteria. It is extremely toxic and must be used with caution as it is lethal if slightly overdosed. It reacts with the proteins in the structure of these pathogens but will also react with koi tissue, turning mucus brown if overdosed.


Protein is provided in koi diets in ingredients such as fishmeal, poultry meal, wheatgerm and cereals. Protein is widely considered to be one of the most significant factors in a koi diet as it is likely to be the most costly element to an artificial diet as well as being the only constituent in a diet than koi can use for growth.

Consequently, many koi keepers place a lot of emphasis on the protein content of a diet, maintaining the higher the protein content of a diet, the better the food.

The science involved means that such logic is not that straightforward for two reasons.

1. The nature of the protein. Using an extreme example to illustrate the point, feathers and fillet stake are both rich sources of animal protein of say at least 70% protein. Which would you rather eat? The answer is obvious and relates to the quality and more specifically the digestibility of the protein (besides the taste!).

The same is true for protein in koi foods. We need to investigate what the sources of protein are in the diet and whether they are digestible and therefore accessible to koi to be used for growth, or whether their structure makes them indigestible and unavailable for growth.

2. The balance in the diet between energy and protein. Unfortunately, koi like to use the expensive protein in a diet as a source of energy, fuelling the activities of swimming, breathing etc. This has two significant implications for the koi keeper. Firstly, if there is not sufficient energy in another form in the diet, such as oils or carbohydrates, then koi will use protein for energy instead of growth, reducing the growth rate. Secondly, when koi use protein for energy, they excrete the nitrogen element of protein that they do not require, in the form of toxic ammonia, causing water quality to deteriorate.

Protein is not simply an issue of quantity, but quality also and it must be fed in a diet that is balanced with other sources of energy.

Pond Pump.

The pump must be the most reliable piece of koi keeping equipment. It is the heart of the pond, recirculating the water through the filtration system, besides performing other aesthetic functions such as giving life to fountains and waterfalls.

Of the two types of pump available, the submersible is by far the more popular as it has a number of key benefits over its external rival. Submersible pumps are easy to install, requiring only very simple plumbing compared to the external pumps and the leading pumps are sold with free 2 or 3 year extended warranties.

Besides their price and guarantee, other considerations when buying a pump are their performance which is usually described as a flow rate given in litres per minute (lpm) or gallons per hour (gph). Such performance figures should also be compared when considering to what ‘head’ you require to pump where the ‘head’ is the vertical distance between the water’s surface and the end of the delivery hose. Even if two [umps are comparable at zero head, their performance is likely to differ greatly when pumping to a given head, and this must be taken into account when buying a pump.

As a pump’s life is now on average 3 years and as most pumps are run continuously, it is prudent to compare the running costs of pond pumps prior to purchase. Power consumption of pond pumps is measured in watts, which is a useful guide to its running cost. Just as two cars with the same fuel consumption can have vastly different performance, the same is true for two pond pumps with the same power consumption. The savings in running costs between two pumps over their lifetime could actually save the price of a replacement pump when it is required. It pays to choose a reliable pump that will deliver your desired flow rate at the cheapest possible running cost.

Kill blanketweed and string algae.