Parasitic organisms known as Gyrodactylus and Dactylogyrtts are the trigger of flukes, which are extremely contagious. They lodge in the gills and under the skin causing the fish to swim about in a wild and jerky manner, suddenly coming to a stop with every appearance of exhaustion.
Again there are numerous treatments for this illness, but the most effective one, in my experience, is the formaldehyde bath. You make up a bath of clear water, to which you add 20 drops per gallon of formaldehyde, then immerse the fish for between 5 to 8 minutes or until it shows signs of discomfort or exhaustion. The treatment should be repeated in two days, after which the fish should be cured.
An additional efficient treatment would be to place the fish in a bath made up of one component of (20 vols) hydrogen peroxide to five-hundred parts of water. The fish should be left in this answer for a number of hours.
When it is essential to treat the majority of fish in an established aquarium, make a answer by dissolving 15 grains of methylene blue in three.5 fluid ounces of water.
This answer is then added to the aquarium in the proportion of one or two cubic centimetres to every gallon of water.
Naturally the water in the aquarium will turn very blue, but within a couple of days it'll regain its regular clarity. It is not essential to change the water, or to repeat the treatment.
An additional technique would be to immerse the affected fish in a bath containing one drop of glacial acetic acid to every ounce of water. Repeat treatment after 48 hours.