Inability to Control Ceratomyxosis in Rainbow Trout and Steelhead with Oral Treatments of Glucan Immunostimulant or the Fumagillin Analog TNP-470

Two oral treatments were tested for their ability to protect migratory hatchery salmonids against infection by the myxozoan parasite Ceratomyxa shasta. Rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) were fed a diet containing either the immunomodulatory compound MacroGard (a glucan from yeast) or the antiparasitic drug fumagillin (from Aspergillus fumigatus). MacroGard was administered in the feed at 2% and 4% of the diet. At the 2% level, the fish were either fed for 14 d before the exposure to the parasite or for 14 d before and after exposure; at the 4% level, the drug was administered for 14 d before the challenge. Fumagillin analog TNP-470 was top-coated on the feed to achieve a dose of 3 or 10 mg × kg fish–1 × d–1. The lower dose was administered for 14 d before exposure or for 14 d before and after exposure; fish given the higher dose were fed the drug only prior to exposure. When administered at 2%, MacroGard significantly increased the mean time to death; howe...