Life cycle of Valvata macrostoma Mörch, 1864 (Gastropoda: Heterobranchia) in the laboratory

Abstract

Laboratory culture in 1994-1999 provided the following data on the life cycle of Valvata macrostoma Mörch: in favourable food conditions female maturity is attained in 60-250 days (mean: 108) at shell diameter 2.40-3.30 mm (rarely more: up to 4.10) and 2.50-3.00 whorls (rarely up to 3.37); in unfavourable conditions the snails mature later, at a somewhat smaller shell size. Snails kept in pairs/groups produce a maximum of 166 cocoons during their lifetime; the cocoons contain a total of up to 1,436 eggs, the number of eggs per cocoon ranging from 0 to 25 (rarely up to 34). Snails kept singly deposit few cocoons and eggs; and the eggs fail to develop. The average life span in favourable food conditions is 383 days, in unfavourable conditions 706 days (maximum 1,192 days). The mean shell size attained in favourable conditions is: diameter 4.46 mm, 3.46 whorls; in unfavourable conditions: diameter 3.65 mm, 3.09 whorls. Mortality of adult snails in laboratory shows a clear seasonal variation, with maximum in June and July.