Treatment of diplomonad intestinal parasites with magnesium sulphate at a commercial rainbow trout (Oncorhynchus mykiss) facility.

Rainbow trout (average weight of 2 g) in fresh water experienced high mortality and were infected with a diplomonad intestinal parasite. Tanks of fish experienced an immediate reduction in mortality after an in-feed treatment with 3% Epsom salts for 2 d. Treatments had to be applied several times, but in each case there was a similar reduction in mortality.