An interesting experiment done by some years ago by Dr. M. Faisal of the University of Alexandria in Egypt. In holding ponds with fish caught directly from the Nile he counted the number of parasites on sections of the gills of fish before and after treatment with various substances used to control gill flukes.
Over a period of a year Dr. Faisal examined a total of 1261 fish. The fish were caught at various times throughout the year and an examination of their gills was made. Sample tissue removed was examined and the number of gill flukes counted. The fish were then treated with various chemicals used at different strengths and timings. The more common chemicals that we come into contact with and use are listed below. One week later a further gill examination was carried out and the parasite population was counted again.
This is the basic summary of his results.
1. Sodium Chloride (salt) used at a 2.5% concentration for 10 mins. killed 62% of the gill parasites with in a week of treatment. (i.e. 2.5Kg course salt per 100l)
2. Potassium Permanganate at 0.2% for 5 mins. Killed 80% of the parasites within a week of treatment. (i.e. 2g/l)
3. Trichlorofon (Neguvon/Dimilin) at 5ppm for 30mins. Killed 83% of the parasites within a week of treatment. (i.e. 0.5g per 100l).
4. Formalin at 50ppm for 24 hours killed 70% of the parasites within a week of treatment. (i.e. 5ml per 100l).
5. Masoten at .25ppm for 24 Hours killed 90% of the parasites within a week of treatment. (i.e. 0.25g per 1000L).
It is interesting to note that a further count was done a month later to check the long term effects of the chemicals. Using the low level of parasites left after treatment as a basis, there was a slight increase in the gill parasite population on the fish that were treated with salt and Potassium Permanganate. However, in the cases where Neguvon, Formalin and Masoten were used, there was a further decrease in the gill parasite population.
Dr. Faisal records his summary thus: "The results show clearly the high efficiency of Masoten in the treatment of Macrogyrodactylus (Gill Fluke) infection in the treated fish. The advantage of Masoten is that concentrations used in the experiment could also be applied in the treatment of fish kept under pond conditions. Besides the Masoten did not disturb the feeding of the fish. Trichlorofon and Naled were also very effective against the worms in the concentration and duration of treatment tested, however, the few surviving monogeneans may constitute a potential hazard of re-infection as the fishes are known to be more susceptible to re-infection following treatment"