Lamella formation and emigration from the water by a laboratory colony of Biomphalaria glabrata (Say) in a flow-through system.

Lamella formation and emigration from the water were investigated in juvenile Biomphalaria glabrata reared at two temperatures in aquaria with a constant water flow. Most snails (97.4%) reared at the lower temperature (21 degrees C) formed lamella at the shell aperture and emigrated from the water, whereas only 10.1% did so at 25 degrees C. Eighty percent of emigrations at 21 degrees C occurred within a period of 15 days, 70-85 days after hatching. A comparison of the studies done so far indicates that the phenomenon may be affected by the ageing of snail colonies kept in the laboratory and their geographic origin, rather than the rearing conditions. This hypothesis, however, requires experimental confirmation.