Blood Fluke Infections in Marine Cultured Fish

Fish blood flukes (FBFs) are the most important digenean parasites in marine finfish aqua culture due to their high pathogenicity. Numerous eggs accumulate in gill lamellae and capillary vessels in various organs, interfere the blood flow. This causes fish to suffocate to death or leads to other fatal health problems. In Japan, important culture fish, such as amberjacks, bluefin tuna and tiger puffer are affected by FBFs of different taxa; namely Paradeontacylix spp., Cardicola spp. and Psettarium spp., respectively. FBFs are relatively host specific and utilize a complex two-host lifecycle. To date, the lifecycles have been elucidated for only a handful marine FBF species and all use terebellid polychaetes as the intermediate host. Chemotherapy with the oral treatment of praziquantel is effective and commonly used in fish farms as a sole control measure against FBFs. The development of prevention method is expected with the recent advances in knowledge on the biology of FBFs.