Organophosphate insecticide for fluke, anchor worm and fish lice on koi and goldfish.

Composition: O,O-dimethyl-2,2,2-trichloro-1-hydroxyethyl phosphonate or O,O-dimethyl-1-hydroxy-2-trichloro methyl phosphonate. Molar mass: 257.436 g/mol

Synonyms: Dipterex, Masoten, Trichlorfon, Metrifonate, Dylox, Negavon, Chlorofos, Bovinox etc (more than 100 names) Very popular! But very dangerous in the wrong hands..

Treatment for ectoparasites like Protozoa (Ichthyophirius, [white spot] Trichodina); Monogenea (Dactylogyrus [gill fluke], Gyrodactylus [body fluke], Benedenia, Cleidodiscus); broad spectrum anthelminthic; Cestoda; Hirudinea; Crustacea (parasitic copepods, Achtheres micropteri, Argulus foliaceus, Argulus sp. [fish lice], Ergasilus sieboldi, Ergasilus sp.[gill maggot], Lernaea cyprinacea [anchor worm], Philometra sp., Salmincola, Sinergasilus major); mollusca [snails]


Pond treatment for koi and goldfish: Active ingredient

1 g/1000 liter in water of average total hardness,

0.5 g/1000 liter in soft water

Two follow-up treatments over two week period is normally recommended.


Do not treat below 18 deg C (fish cannot metabolise/excrete it fast enough)

Do not treat above 28 deg C (uptake rate is too high)

It may be more toxic to other aquarium fish, orfe and rudd

It is toxic to sharks (tropical fish)

It can be removed by activated charcoal.

Once opened store in a dark, airtight container.

Do not use it when it old (it looses it's bluish colour) but it may be revitalized by heating

Work carefully with it like any other toxic compound and don’t inhale the dust. Wear gloves and protection gear.

Other information

Frequently used in Koi keeping because effectiveness against various flukes (both gill and body fluke), fish lice, anchor worm, Ergasilus. Also Cestoda (tape worms), Hirudinae (leeches) and snails. Preferred treatment for fluke on goldfish.

Will kill most insects and must be used with care for environment. Degrades quickly in pond conditions, but can cause disorientation and nervous disorder if used incorrectly. Typical symptoms of overdosing in koi is a bent spine and nervous, wip-like swimming. The fish may recover over a period of a year or two, but mostly won’t. The effect may also get worse over time.

We found it very effective in combination with salt as a prophylactic “first treatment” after harvest from the mud dams. We would prepare the receiving holding tank in advance with 0.5 g/1000 Trichorfon and 3 kg/1000 litre salt (sodium chloride) for the first day. Then check the next day for parasites to decide on further treatment

About warm water aquaria:

Our experience is with koi and goldfish, but our gut feel is that this temperature sensitivity to Dipterex is the reason that warm water aquaria has problems with it. The rate of metabolism varies with fish species. So working with this knowledge one can still use it quite effectively. If you want to kill gogo's like leaches and snails and water beetle etc in your tank, remove the fish to another tank (at same temperature) for 24 hrs while treating your tank. Remove any active carbon filtration and replace after the treatment. But if you want to treat for things like fluke or worms that are on the fish, move the fish into a clean tank, no gravel, no filter, only air, but clean water at same temperature, for 4-6 hours, and move it back to its home after treatment.


Triclorfon is an irreversible organophosphate acetylcholinesterase inhibitor. It is a prodrug which is activated non-enzymatically into 2,2-dichlorovinyl dimethyl phosphate.

AChE is found at mainly neuromuscular junctions and cholinergic brain synapses, where its activity serves to terminate synaptic transmission. That explains the reaction to the nervous system to overdosing. It is the primary target of inhibition by organophosphorus compounds such as nerve agents and pesticides.

Sources: Personal experience and. various databases, articles eg

Herwig N (1979) Handbook of Drugs and Chemicals Used in the Treatment of Fish Diseases: A Manual of Fish Pharmacology and Materia Medica. Charles C. Thomas, Publishers, Springfield, Ill. p272.

PAN Pesticides Database. http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC33346 Accessed 17/10/2014

PupChem. http://pubchem.ncbi.nlm.nih.gov//compound/5853?from=summary accessed 17/10/2014

Wikipedia, http://en.wikipedia.org/wiki/Metrifonate accessed 17/10/2014

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