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Leeches can be a problem in a pond, especially if it a planted one. Although not frequently encountered, leeches do appear in ponds. It is normally introduced through new plants, new fish, live food and visiting wildlife. Observing a leech making a meal of the blood supply of a favourite Koi is not pleasant. It can be seen firmly attached to the fish and its body contracting and expanding as it feeds. Worst is the fact that when a leech is spotted on a fish, chances are that many more is already in the pond, waiting to attach themselves to the other Koi in your collection. Leeches attach themselves to a host Koi with their sucking mouth parts. These mouth parts are then used to draw blood as a food source from the host Koi. The health risks that pertain to all parasites with the ability to damage the body or gills of fish apply to the leech. There are always the potential secondary infections and the actual transmission of disease. The fish leech is known to carry and transmit organisms that in turn parasitize the blood and major organs of fish. There is also the added risk of anaemia.



Leeches (Piscicola geometra) resembles a brown worm but the colour can vary depending how recently a meal of blood has been digested. On close examination through a magnifying glass or sometimes with the naked eye, the leech can be seen to have a geometric banded body pattern. The name geometra was derived from this pattern. It can grow up to 8 cm in length. Many organisms in the pond may resemble a fish leech and some may even be members of the same family. They may be found in the filter system and on plants. The size may differ from species to species but they are normally brown, grey and even red. However, unless the organism is found attached to the body of a koi, it may not be a fish leech.


Leeches may be present in a pond and will go unnoticed for some time because it normally attach itself for a period of two to three days and then leaves the host to lay eggs. They attaché themselves to anywhere on the body of the Koi but favour the areas where there are no scales like the underside of the body, the face, mouth, and the ball joints of the pectoral fins. It is therefore necessary to check the underside of a Koi when leeches are suspected. A tell-tale sign of leech infestation is also the presence of red lesions on the skin. These lesions are caused by the leech attaching itself to the fish and drawing blood.



Although it will not be possible to inspect every hiding place for leeches on new plants, inspect them carefully. Avoid live food and rather opt for frozen or treated substitutes. It is also hard to stop frogs and birds from visiting ponds and one should therefore avoid encouraging these visitors to the pond.


Life cycle





Eradicating leeches from a pond is difficult for several reasons. Leeches lay their eggs in tough leathery cocoons that are impermeable to any chemical treatment. It can therefore only be treated when hatched. There are only two effective ways of eradicating leeches from a pond once it is infected. The first is repeated dosages of organophosphates. This treatment is actually a nerve poison and may not be the answer as during cooler months the eggs may take several weeks to months to hatch. Repeated treatment for such a long time will prove fatal for your fish. The second is complete drainage and drying of the pond. The pond should be drained and allowed to dry completely for several days as this will kill the adults and eggs. Plants should be discarded and pumps should be sterilised. Filter material can also be a hiding place or may contain eggs. Plumbing should also receive attention as some eggs may be present in the pipes. When returning the koi, each one should be examined and leeches should be manually removed. Remember to apply topical treatments to lesions to prevent secondary infections.


Last Updated on Monday, 12 January 2009 12:49