German scientists study malachite green alternative

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Scientists in Germany have published the results of a study investigating the performance of an alternative whitespot medication following a ban on the use of malachite green.

Experts from the Leibniz-lnstitut fr Gewsserkologie und Binnenfischerei in Berlin investigated the use of peracetic acid (PAA) on Zander, Sander lucioperca, that had been infected with the ciliate protozoan parasite Ichthyophthirius multifiliis.

Their findings, which have just been published in German in the journal Deutsche tierrztliche Wochenschrift explain the results of their initial study to determine the effectiveness of the chemical and its toxicity to fish.

State of emergencyThe authors said that following Germany's ban on the therapeutic use of malachite green to treat fish diseases, they faced "a state of emergency for the treatment of ichthyophthiriasis", but believe that PAA might be a potential alternative in its absence.

However, the treatment is unable to fight parasitic trophonts when they are present within the tissues of the fish.

The authors wrote: "For juvenile sander (length 3 cm) we determined a 24-h-LC50 of 1.14 (0.97; 1.3) ppm PES. In two investigations PAA was applied in daily intervals of 0.5; 1, 3, 5 and 24 h and concentrations of 0.5; 1; 1.5 and 2 ppm to treat I.-m.-infection in sander.

"In test I all sander (length 9 cm) died as a result of the I.-m.-infection. However, the PAA exposed fish survived longer than the PES-free controls! This might be due to a disinfection of other pathogens by PAA.

"In test II, the fish (length 12 cm) were less infected than fish in test I. Four of six fish died in the group exposed with 2 ppm PAA for 24 hours. The abundance of I.-m.-trophonts was determined in mucus, fin and gill tissues of all fish.

"Significant differences could not be observed between test I and test II because of dissimilar: 1. exposure in time and concentration, 2. age and condition of the fish and 3. homogenity of the variances."

It is believed that, like malachite green, peracetic acid is only capable of killing the free living stages of the whitespot parasite and does not appear to be able to kill the trophonts embedded in fish tissue.

Alternative medicinesPrevious studies have shown that non-malachite green treatments are less effective for the treatment of whitespot.

Scientists from the University of Oulu in Finland published a study in 2005 which showed that virtually all alternative treatments for whitespot were less effective than the malachite green and formalin combinations they were designed to replace. (See Non-malachite whitespot treatments less effective).

Malachite green is a known carcinogen (cancer causing agent) and is banned for use in the production of food fish around the world.

However, it currently remains legal to use for the treatment of pet fishes in the UK.

Meinelt T, Richert I, Stber A, Brunig I (2007) - Application of peracetic acid to the parasite Ichthyophthirius-multifiliis in Sander (Sander lucioperca) breeding. Dtsch Tierarztl Wochenschr. 2007 Jul;114(7):244-51. (In German).