Strain differences in Helix pomatia L. (Gastropoda: Pulmonata): diapause, digging, growth rate and shell fill.

Abstract

This strain comparison followed from a pilot project to evaluate the technical feasibility of farming Helix pomatia in north-west Bulgaria, where the wild population of the species is of some economic importance as a source of edible snails for export. The original parent stock for that project were adults collected from a wild population in the Mezdra area in the spring of 1996, and introduced into open, spray-irrigated field pens planted with leaf beet and fodder rape a few kilometres from the collection site; snail meal was supplied ad libitum in covered feeders. From growth marks on the shell it was estimated that these snails had taken 4‐5 years to reach adult size. At the time of collection they weighed an average of 26 g. The least shell diameter, as measured by the size of a round hole through which the shell could not pass, ranged from 31 to 40 mm. In 1996, 1997 and 1998 both these snails and their offspring went into diapause in August, waking only in the following spring, and growth of the young (F1) snails stopped much earlier in spite of apparently favourable conditions. Diapause is distinguished from a temporary torpor by the physiological preparations made for it—a halt to growth and a hardening of the edge of the shell of young snails—combined with a refractoriness to resumption of growth and activity if the diapause is artificially interrupted. 1,2 Glycogen reserves are accumulated in preparation for diapause. 3