Efficacy of fumagillin against proliferative kidney disease and its toxic side effects in rainbow trout (Oncorhynchus mykiss) fingerlings.

Abstract

The potential of fumagillin DCH to prevent proliferative kidney disease (PKD) in rainbow trout fingerlings was tested in field and laboratory studies. In a field study, PKX trophozoites and accompanying inflammation (PKD) occurred in the kidneys of 92.7% of fish fed control diets and in only 7.9% of fish receiving 0.34 g fumagillin/kg of diet (fed at 6% biomass per day) when examined 65 days after being placed in waters enzootic for the parasite.In a laboratory study, fumagillin treatment reduced the number of fish that developed PKD following natural exposure to the parasite. In both the laboratory and the field studies, fish fed fumagillin demonstrated a loss of appetite beginning 2 to 4 weeks following feeding of medicated diets. Cumulative mortalities of 92% and 33% for the field and laboratory studies were experienced by groups of fish continuously fed medicated diets.The toxicity of fumagillin was evaluated in the laboratory following feeding at 0.1, 0.25, 0.5 or 1.0 g drug/kg feed (fed at 1.5-2.0% biomass daily) for 8 weeks at water temperature of 15°C. Fish administered 0.5 and 1.0 g drug/kg food exhibited anorexia beginning 4 weeks after initiation of feeding that lasted until the end of the experiment at 8 weeks. The cumulative mortality of fish fed the 1.0 g drug/kg reached 22% at the end of the study. The average weight of these fish was significantly decreased compared to fish receiving lower doses or no fumagillin in the diet. The spleen and kidney of fish administered the two highest doses of fumagillin were grossly reduced in size. Microscopic examinations revealed a decrease in the amount of interstitial hematopoietic tissue in the anterior and posterior kidney and splenic lymphoid tissue. These effects were least apparent in the fish fed 0.1 g fumagillin/kg feed. These results indicate that fumagillin can have an adverse effect on the hematopoietic tissue of fish when administered at increased concentrations over an extended period of time. However, these effects can be minimized when fish are fed low doses of fumagillin as a potential treatment to prevent PKD.