A PRELIMINARY STUDY ON REPRODUCTION AND GROWTH OF THE SNAIL,BELLAMYA AERUGINOSA (VEEVE)

Bellamya aeruginosa (Veeve) is a viviparid gastropod widely distributed in China and of outstanding importance among food items of the Snail Carp,Mylopharyngodonpiceus.Investigations referring to the reproduction and growth of this snail basedon the methods of out-door rearing,laboratory culture and field observations weremade during March 1963-June 1964.The results may be briefly summarized as fol-lows:1.The sex ratio of natural population is in close agreement with the expectedvalue of 1∶1 as tested by goodness of fit.2.Mature females are pregnant throughout the year while the number of embryospossessed by each individual varies in different months.Maximal number of embryos(15.9/female) was found in early May and the minimal (3.6—4.3/female) in July-September.It has also been found that females of larger size usually possess moreembryos and individuals inhabiting the pond have relatively larger number of embryosthan those inhabiting the lake.3.The breeding season of the animal lasts from middle April to late November,but most offspring are born in June.The threshold water-temperature for repro-duction was found to be about 16—18℃ and the optimal water-temperature,ca.26℃.4.Reproduction takes place when an individual attains to a shell-height of 15—16 mm (0.81—0.94g.in body weight).The natality rate of young females is cons-picuously lower (only 4.3/female in June).Than that of females of middle age(29.5/female in June).The average number of young reproduced by a female in ayear has been calculated as 49.7.5.The appearance of the new-born animals is not entirely similar to that of theadults.In contrast to the fact that shell-height exceeds shell-width in the adults,about 90% of new-born individuals have their shell-height smaller than shell-width.The new-born individuals are 3.85 mm in height and 4.11mm in width.6.In favourable season,the growth of juveniles in a shallow lake may be expres-sed by the following empirical formulae:For shell-height:L=26-21.83e-0.007t For body weight:W=0.55(26-21.83e-0.007t)2.692 (Where L denotes shell height in mm;W,body weight in mg;t,time innumber of days).7.Formulae of allometric growth have been computed as follows:For individualswith shell-height over 4.3 mm:W=0.551 L2.692 W=0.149 B3.633B=0.539 L+2.420 For individuals with shell-height under 4.3 mm:W′=1.012 L′2.004 W′=0.339 B′2.662 B′=0.827 L′+0.965 (Where W or W′ represents body weight in mg;L or L′,shell-height inmm;B or B′ shell-width in mm).