The effect of low zinc concentrations on some demographic parameters of Biomphalaria glabrata (Say), mollusca: gastropoda

The effects of low zinc concentrations on the freshwater snail Biomphalaria glabrata (Say) were measured under continuous flow conditions. The time of sexual maturity of young snails, the fecundity and fertility of the adults and the mortality and growth-rate of both stages were investigated. Embryos and snails were exposed to zinc concentrations ranging from 500 ppb to >5000 ppb. The mortality of embryos and young and adult animals rose with increasing zinc concentration. Thirty-three days after the experiment was started, 20% of the adults and 60% of the young individuals died in 1500 ppb Zn 2+, whereas in the control all the animals survived. Embryos did not hatch in 1000 ppb Zn 2+. Fecundity was significantly lowered by 500 and 1500 ppb Zn 2+ and completely suppressed by 3000 ppb. Fertility was lowered by 500 ppb Zn 2+ and the embryos showed a decreasing hatch-rate during the time of experimentation. In respect to the control, 500 ppb Zn 2+ reduced the growth-rate of adult and young animals to about 50%. At 500 ppb sexual maturity was delayed for about 7 days. Higher concentrations prevented growth and the attainment of sexual maturity.