koi4u-2011 facebook  koi4u-2011 hoogland
You are here: HomeKoi HealthMedicationOrganophosphates





Organophosphates are potentially dangerous to both fish and humans. More detail are available on this site. Because of the potential dangers, the indiscriminate elimination of invertebrates in natural systems as well as the cumulative effect in fish tissue, the use of organophosphates in fish disease control has been banned in many countries. The most widely used organophosphate in the treatment of Koi is Trichlorfon. Trichlorfon is listed as an active ingredient in various insecticides, but because of the varying concentrations in different preparations, I prefer Trichlorfon powder obtainable from agricultural stores.



Trichlorfon is a white, dull powder that should be stored in an airtight container. Once it becomes lumpy or moist, it may be toxic and is best safely discarded. Trichlorfon will treat diseases caused by multicellular parasites, such as Gyrodactylus (skin fluke), Dactylogyrus (gill fluke), Neobenedenia (flukes), Argulus (fish lice), Lernaea (anchorworm) and leeches. Some reports indicated that it is also effective against Ichthyophthirius and Trichodina.

Organophosphates, work by interfering with the nervous system and thus affect the vital physiological processes in a long list of organisms. Of interest to the Koi keeper is that it is toxic to amphibians, shrimps, snails, and the parasites as listed above. If you have some snails or other non-fish/invertebrate life in the treated system you'd like to keep, you will have to remove them; returning them only after the parasite problem is cured and the chemical is removed by time or water changes.

When Trichlorfon is added to water it degrades to DDVP, which then slowly degrades to less toxic by-products. The rate at which it degrades is speeded up by various factors like sunlight, high temperatures, aeration and high pH. All speed up degradation. In mild temperatures and moderate pH it can remain in the water for several days. In alkaline conditions and high temperatures DDVP can degrade within a day. Therefore the quicker it breaks down, the higher the initial dose needs to be.


Use 2 to 3 doses a week apart to deal with emerging larvae and Juveniles.

Below 27 degrees Celsius: 1 gram per 4000 litre.

Above 27 degrees Celsius: 1 gram per 2000 litre.

Mix the required amount of Trichlorfon powder in a bucket of pond water and distribute it evenly around the pond.

As with all organophosphate pesticides, you should avoid physical contact as far as possible. If you over-treat your fish, you will see erratic behaviour, darkened colour, listlessness, clamp fins or rapid gill movement. If this occurs, you should make a large water change immediately.

Repeated dosages can lead to a build-up in the fish’s tissues and may prove fatal. An article about the possible effects of overdosing with organophosphates, can be viewed here.


Last Updated on Wednesday, 29 February 2012 12:52