The Effect of Density Changes On the Reproduction of the Pond Snail Lymnaea Stagnalis (L.)

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Abstract
Progress in this laboratory in the study of freshwater snails (especially Lymnaea stagnalis) has necessitated the use of increasingly large numbers of experimental animals. It is evident that the performance of experi- ments with a great number of snails must be accompanied with an improved control of environment and a facilitation of routine tending procedures. Experimental tanks as described by VAN DER STEEN, VAN DEN HOVEN & JAGER ( 1969) meet these demands and allow large- scale breeding. The relevant set-up includes provisions for constant and continuous water change, beside regulated light and temperature conditions. As many as 2,500 sexually mature snails (Lymnaea stagnalis) developed within a few months from capsules put into a tank at the start of a breeding experiment. Unfortunately, a comparatively high mortality among the adults ensued, although the fecundity remained high. Subsequent, preliminary experiments (not published) indicated that the mortality is greatly reduced when the density is gradually de- creased from the early adult stage onwards. Another observation concerned the interrelations between adults and young. The growth of newly hatched individuals came near a standstill in tanks that, beside capsules, contained adults from the start. These data suggest that the effects of density in Lymnaea stagnalis are worth a further study, the more so since evidence for the effects of density in freshwater snails is as yet scanty (cf. JOBIN & MICHELSON, 1967).

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