Infections with gill parasites (monogeneans, digenean metacercariae, myxosporeans, ciliates) in carp fry (Cyprinus carpio) were followed for 7 weeks after hatching in a freshwater earth pond after natural spawning. The pond was situated in Sukabumi (Indonesia) in a tropical climate and the water temperature varied between 24.5 and 27.6°C. Infections with Dactylogyrus minutus were most prominent during the period of investigation but also D. extensus, Gyrodactylus sp. and diporpa larvae occurred. Echinostomid metacercariae showed a steady increase in occurrence, whereas the abundance of trichodinids varied notably, with a significant peak 14 days after hatching. Cysts of the myxosporeans Myxobolus toyamai and Thelohanellus callisporis were detected from day 23 posthatching. Examination of one spawner indicated that these fishes are part of the infection source for Dactylogyrus minutus and D. extensus. Waterbath treatment with mebendazole (1 mg/l) for 24 h resulted in a significant reduction of the number of Dactylogyrus minutus on carp fry. Prophylactic treatments with fumagillin (0.1% in feed) for 14 days from day 14 posthatching inhibited development of myxosporean gill cysts.