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Studies on Reproduction and Growth of Oncomelania Quadrasi, O. Nosophora, and O. Formosana, Snail Hosts of Schistosoma Japonicum¹

Oncomelania quadrasi and O. nosophora females, when mated and isolated as pairs, laid an average of 0.7 eggs per day. The frequency of egg-laying ranged from daily to a lapse of about 50 days. The maximum number of eggs laid by a female snail in a single day was 24 for O. nosophora and 23 for O. quadrasi. O. formosana laid an average of 1.3 eggs per day, and the maximum number of eggs laid by one snail in one day was 19. The frequency of egg laying ranged from daily to an interval of 12 days. The average incubation periods for eggs for O. quadrasi, O. nosophora, and O. formosana were 18.4, 21.4, and 19.5 days respectively. The average sizes of the eggs with capsules of the three species in the same order were 0.6, 1.1, and 1.0 mm., while the average sizes of the newly hatched snails were 0.5, 0.6, and 0.55 mm.

The growth rates for O. quadrasi, O. nosophora, and O. formosana were 0.2 mm., 0.4 mm., and 0.3 mm. per week respectively. In general, the males and females grow at approximately the same rate for the first 11 weeks for O. quadrasi and 16 weeks for O. nosophora. At this time the rate of the males was reduced and size dimorphism occurred.

Female snails were raised from isolated eggs and were followed through to maturity. They were mated only once to male snails reared under the same conditions. After the mating and isolation, O. quadrasi, O. nosophora, and O. formosana produced young snails for average observation periods of 285, 180, and 135 days respectively. The maximum periods of reproduction per species were 385, 213, and 200 days respectively. Snails were found to be able to produce several hundred young from one mating.

The duration of copulation of O. quadrasi is from about one hour to four and one-half hours and for O. nosophora about one hour to five and one-half hours. O. nosophora does not copulate as readily as O. quadrasi.

¹ This work was conducted under the sponsorship of the Commission on Parasitic Diseases, Armed Forces Epidemiological Board and was supported by the Office of the Surgeon General, Department of the Army, under Contract No. DA-49-007-MD-307.