In 1989 the total aquaculture production in Indonesia reached 466 704 tonnes of which the production in freshwater ponds amounted to 113 673 tonnes. The most important species in this production type is the common carp (Cyprinus carpio) (34 601 tonnes). In addition, carp is also the most important species in paddyfield fish production (89 616 tonnes) and in freshwater netcage culture (4924 tonnes). Therefore, the production-limiting fish parasite infections in carps and their control are of high interest. From 7 days post-hatching, carp fry (20 specimens in each sample) were collected weekly from pond no. 59 at the Freshwater Aquaculture Development Centre in Sukabumi, Indonesia. Fish were brought to the laboratory and dissected, and their gill arches were mounted on slides in water and examined under the compound microscope (40-1000 magnification). The carp fry were found to be infected with the monogeneans Dactylogyrus minutus, D. extensus, Gyrodactylus sp., the myxosporeans Myxobolus toyamai, Thelohanellus callisporis, digenean metacercariae and trichodinids. The benzimidazole, mebendazole (Vermox vet., suspension, Janssen), was used in laboratory aquaria as waterbath treatment (1 mg MBZ/l) (24 h at a temperature of 24-26°C) against Dactylogyrus minutus on carp fry (24 days post-hatching). Treated and non-treated controls (20 specimens in each group) were examined for infection 3 days post-treatment. The antibiotic, fumagillin, was used in feed (0.1% drug in commercial dry feed) in laboratory aquaria (in duplicate) for carp fry from 14 to 28 days post-hatching. After additional 14 days the fish were examined for myxosporean infection (15 and 20 specimens in the medicated groups and 25 and 20 specimens in the non-medicated controls). In both the MBZ and fumagillin trials the carp fry had been exposed to natural infection in the carp pond before transfer to the laboratory. Waterbath treatment (laboratory trials) with mebendazole (1 mg/l) for 24 h was effective against dactylogyrosis and a feeding regime with fumagillin-containing feed (0.1%) for 14 days prevented the development of myxosporean cysts in carp fry.