POPULATION-DENSITY EFFECTS ON GROWTH IN CULTURE OF THE EDIBLE SNAIL HELIX-ASPERSA VAR MAXIMA

The effects of population density on the growth of H. aspersa Muller v ar. maxima under controlled environmental conditions were examined. In hibitory 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 populat ion densities, enhanced snail growth was observed when the frequency o f container cleaning was increased to a two-day interval. No significa nt differences were recorded, following 19 weeks growth, between final mean weights of snails from containers cleaned less frequently. The l owest snail mortality was consistently recorded at the lowest populati on density in the most frequently cleaned containers. At all snail pop ulation densities three phases of growth were observed: (a) lag (0-5 w eeks), (b) rapid (6-15 weeks) and (c) stable (16 weeks and over). Duri ng the first three weeks of growth, high population density had a posi tive effect on diet consumption, food conversion efficiency and snail growth. Adverse population density effects increased progressively dur ing phase (b), typically following 9 weeks growth. Juvenile snails tra nsferred from high to low population densities during phase (b) contin ued to exhibit slower growth rates associated with high population den sities. Food conversion efficiency of snails in all treatments decreas ed throughout the experimental period but with no overall effect of co ntainer cleaning frequency apparent. Inherent growth variability of si bling snails was unaffected by population density or container cleanin g frequency. The importance of the results for intensive snail culture is discussed.