魚 病 研 究 Fish Pathology, 25 (3), 141-146, 1990. 9 Efficacy of Fumagillin Against Proliferative Kidney Disease and its Toxic Side Effects in Rainbow Trout (Oncorhynchusmykiss) Fingerlings A. WISHKOVSKY1*, J. M. GROFF1, D. J. LAUREN1, R. J. TOTH2 and R. P. HEDRICK1** Department of Medicine, School of1 Veterinary Medicine, University of California, Davis, California 95616, USA California Department of Fish and Game, Bishop, California 293514, USA (Received April 13, 1990) 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•Ž. 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 cumu lative 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. How ever, these effects can be minimized when fish are fed low doses of fumagillin as a potential treatment to prevent PKD. The antibiotic, fumagillin DCH, has been and myxosporean diseases of fish has also been found to be effective in controlling diseases reported (KANO et al., 1982; MOLNAR et al., caused by certain microsporidia in insects 1987; HEDRICKet al., 1988a). BAILEY, 1953; LYNCH and LEWIS, 1971), and The myxosporean PKX, is the cause of primarily to control Nosema infection of honey proliferative kidney disease (PKD), one of the bees (KATZNELSON and JAMIESON, 1952). The most serious diseases of farm-reared salmonids potential of the drug for treating microsporidian in Europe and North America (CLIFTON * Current address: Ministry of Agriculture HADLEY et al., 1984; HEDRICK et al., 1986). , Fish eries Division, Laboratory for Research of Fish Recent reports have shown that treatments and Diseases, Nir David 19150, Israel. effective prophylaxis of this disease is possible. ** To whom correspondence should be directed . Periodic malachite green bath or flush treat 142 A. WISHKOVSKY, J. M. GROFF, D. J. LAUREN, R. J. TOTH and R. P. HEDRICK ments can reduce the severity and incidence of trout were fed at 6% biomass per day. of PKD in rainbow trout (Oncorhynchus mykiss), Cumulative mortalities were estimated by the but this compound can be toxic to fish and is number of survivors at the end of the study. considered unsafe for food fish due to its po After 65 days, the kidneys and spleens of 76 tential teratogenic properties (ALDERMAN and experimental and 82 control fish were removed, CLIFTON-HADLEY, 1988; ALDERMAN, 1985). fixed in DAVIDSON'S solution (HUMASON, 1979), Preliminary studies in our laboratory indicated embedded in paraffin, sectioned to 6 ƒÊm, and that chinook salmon (O. tshawytscha) finger stained with hematoxylin and eosin. The lings experimentally-infected with PKX were kidney sections were examined for PKX and protected from PKD when fumagillin was any pathological changes. administered in the diet. In contrast, 90-100% of the untreated fish developed PKD (HEDRICK Efficacy of Fumagillin on Naturally-Acquired et al.,1988a). Infection: Laboratory Study In this paper we report on field and labor Rainbow trout fingerlings (mean weight 39.7 atory studies conducted to examine the efficacy g) were obtained from a PKD enzootic area of extended oral administration of fumagillin to (State of California American River Hatchery, protect against PKD in naturally-infected Rancho Cordova, California) during an active fingerling rainbow trout. In addition, the ef infection. Fish (35.0 g) from the same stock fect of selected drug doses on the growth of were moved to the laboratory 3 mo earlier, a fish and possible toxic effects were examined time at which infectivity is absent from the in laboratory studies. hatchery water supply (FOOTT and HEDRICK, 1987), and were treated as uninfected controls. Materials and Methods At the initiation of the experiment, 20 fish from each group were examined for PKD. Two Medicated Diets groups of infected fish (70 fish each) and two Fumagillin DCH dissolved in 100% isopropyl control groups (50 fish each) were placed in ethanol in the field study or in 95% ethanol for 130 l aquaria supplied with flow through aerated subsequent experiments was sprayed onto a com well water (15•Ž). One group of the experi mercial pelleted feed (100 ml alcohol solution/ mental fish and one control group were fed kg feed). These pellets were then coated by fumagillin diet (1.0 g drug/kg diet fed at 1.5% spraying with a mixture of alcohol and cod body weight daily); the other two remaining liver oil (50 ml of each/kg feed) and allowed to groups were fed unmedicated diet. Feeding of dry. Medicated and control feeds were stored medicated diet began immediately after in at -20•Ž immediately after preparation. fected fish were transferred to the laboratory and was continued until week 5. Beginning at Efficacy of Fumagillin: Field Studies week 5 until the end of the study at 8 weeks, The field studies were conducted with rain all groups received unmedicated diets. Mor bow trout at the State of California Hot Creek talities were recorded daily. Kidneys from 10 Hatchery, Bishop, California. This site has a fish in each group were taken and processed water supply with an annual history of PKD for routine histopathological examination at 4 infectivity (HEDRICK et al., 1988b). Water and 8 weeks after the initiation of the temperature at this location is a constant experiment. 14.5•Ž. Two groups of 1000 rainbow trout (mean Toxic Effects of Fumagillin: Laboratory Study weight of 2.0 g) were transferred to adjacent Because field studies indicated that increased compartments in a raceway receiving water doses of fumagillin resulted in an adverse toxic known to contain the infective stage of PKX. effect, a laboratory study was designed to One group was fed a commercial (unmedicated) determine the effects of selected concentrations diet and the second group fumagillin medicated of the drug on rainbow trout fingerlings. Fish feed (0.34 g fumagillin/kg feed). Both groups (mean weight of 3.89•}0.2 g, and mean fork Effect of Fumagillin on Rainbow Trout Fingerlings 143 length of 6.65•}0.11 cm) were obtained from a commercial culture facility in California with no history of PKD. The fish were fed a com- mercial diet at 1.5-2% of their body weight daily. Twenty groups of 18 fish each were maintained in 10l aquaria supplied with flow through aerated well water (15•Ž). Four groups of fish (72 fish) were fed either 1.0, 0.5, 0.25, or 0.1 g of fumagillin per kg of feed. A fifth group received an unmedicated control diet. Mortalities were removed and recorded daily. At 1, 2, 4, and 8 weeks after beginning the experiment, 18 fish from each treatment were euthanized in 0.5 g,/‚Œ tricaine methanesulfonate (MS-222) and body weight and length measure- ments were recorded. Heart, intestine, kid- ney, liver and spleen were taken from 10 ran- domly sampled fish from each group on 4 and 8 weeks after initiation of the study and pro- cessed for histopathological examinations. Results Fig. 1. Proliferative kidney disease (PKD) and PKX trophozoites in rainbow trout receiv- Efficacy of Fumagillin ing unmedicated diets after natural expo- At the end of the field study (week 8) only sures to the parasite. (A) Interstitial in- 6 of 76 (7.9%) of the fumagillin-treated fish flammation in the kidney. Bar=1 mm. (B) contained PKX parasites and renal interstitial PKX trophozoites (arrows). Bar=10ƒÊm. inflammation. In contrast 76,82 (92.7%) of the Hematoxylin and eosin stains. kidneys from control fish were infected (Fig. 1). Experimental fish exhibited a loss of appetite the control group fed unmedicated diet. Be- beginning at week 4. While only about 5% of cause of this mortality, feeding of the medi- the control group died over the 8 week period, cated feed was terminated at the end of week a high cumulative mortality (92%) occurred in 4, and all groups were fed control feed until the medicated group by the end of the study.