POPULATION DENSITY EFFECTS ON GROWTH IN CULTURE OF THE EDIBLE SNAIL <i>HELIX ASPERSA</i> VAR. <i>MAXIMA</i>

Abstract

The effects of population density on the growth of H. aspersa MÜller var. maxima under controlled environmental conditions were examined. Inhibitory effects on snail growth and maturity resulting from increased population density, between 100–800 snails m−2 of floor area, were observed for a range of container cleaning frequencies. At all population densities, enhanced snail growth was observed when the frequency of container cleaning was increased to a two-day interval. No significant differences were recorded, following 19 weeks growth, between final mean weights of snails from containers cleaned less frequently. The lowest snail mortality was consistently recorded at the lowest population density in the most frequently cleaned containers. At all snail population densities three phases of growth were observed: (a) lag (0–5 weeks), (b) rapid (6–15 weeks) and (c) stable (16 weeks and over). During the first three weeks of growth, high population density had a positive effect on diet consumption, food conversion efficiency and snail growth. Adverse population density effects increased progressively during phase (b), typically following 9 weeks growth. Juvenile snails transferred from high to low population densities during phase (b) continued to exhibit slower growth rates associated with high population densities. Food conversion efficiency of snails in all treatments decreased throughout the experimental period but with no overall effect of container cleaning frequency apparent. Inherent growth variability of sibling snails was unaffected by population density or container cleaning frequency. The importance of the results for intensive snail culture is discussed.