Author
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Mitchell, Andrew |
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HOBBS, MELISSA - WILLIAMS BAPTIST COLLEGE |
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Submitted to: Parassitologia
Publication Type: Abstract Only Publication Acceptance Date: 4/11/2007 Publication Date: 9/24/2007 Citation: Mitchell, A.J., Hobbs, M.S. 2007. Efficacy of 6-, 12-, and 24-h bath treatments against Bothriocephalus acheilognathi infection in grass carp Ctenopharyngodon idella and the toxicity of praziquantel to C. idella [abstract]. Proceedings of the International Symposium on Fish Parasites. Parassitologia. 49:375. Interpretive Summary: Technical Abstract: Bothriocephalus acheilognathi is an intestinal tapeworm found in freshwater fish (usually cyprinids) throughout the world and has been in the USA since 1974. It affects the health of fish by slowing growth, lowering the fish’s ability to withstand harvesting procedures, shortening life span, and occasionally killing fish. A number of states in the USA allow only B. acheilognathi-free fish to be imported and these shipment restrictions are of a greater economic impact for commercially fish producers than are the health issues. Few methods have been developed that eliminate tapeworms from infected fish. Praziquantel is an anthelmintic that has been shown to reduce tapeworm numbers when injected, fed (naturally or forced), or treated as a water bath. Anthelmintic medicated feeds are often not consumed by all fish, potentially leaving infected fish in a treated population. Bath treatments are preferred because they are not as labour intensive as injection and force feeding methods and because they target all fish in the treated population, giving the potential for elimination of all tape! worms. Tests were performed to determine the 96- and 24-h toxicity of praziquantel to grass carp Ctenopharyngodon idella (2.3 g and 9.1 g of fish/L of water were used for the 96- and 24-h tests, respectively -- average fish size was 9.1 g). Tests were also performed to determine the efficacy of praziquantel water bath treatments (0.5 to 12 mg/L) given for 6-, 12-, and 24-h exposures (30-90 g fish were used). In later tests, 12-h treatments (0.75 and 1.5 mg/L) were applied twice with a 3-d interval between applications. Efficacy studies were carried out at either 6 g of fish/L of water or 60 g/L (a high, commercial holding-tank, fish density). All treatments were carried out in aerated static water containers stocked with C. idella naturally infected with B. acheilognathi (60 to 100% incidence). A stock solution of praziquantel made at a rate of 12.5 mg/mL of 70% ethanol or isopropanol was added to the water to give the appropriate chemical concentration. All tests were run at 19 to 25°C. Fish were held 3- and 4-d post-treatment in flow through water tanks for efficacy and toxicity tests, respectively before results were obtained. The 24- and 96-h LC50 values for praziquantel to C. idella were 63.4 and 60.6 mg/L, respectively. The 24- and 96-h LC0 values were 60.0 and 60.0 mg/L, respectively. Most praziquantel treatments tested significantly reduced the incidence of tapeworms and some were highly effective, resulting in less than a 5 % tapeworm incidence. These included 3 mg/L and higher treatments for 12 h at 60 g/L fish density, 6 mg/L and higher treatments for 6 h at 60 g/L, and a twice-applied 12-h treatment of 1.5 mg/L at 60 g/L. Only one treatment (1.5 mg/L for 24 h at 6 g/L fish density) eliminated all tapeworms from infected C. idella. Praziquantel is a safe and effective treatment for B. acheilognathi infected C. idella. Fish density and possibly the concentration of tapeworms in the intestinal tract of fish affect the efficacy of treatments. Further testing is planned to determine a treatment that will eliminate all B. acheilognathi from fish stocked at a 60 g/L fish density. |
