RESUMO
The LC50 and LC90 of ammonium chloride [NH4C1] were found to be 90 ppm and 130 ppm, respectively. Maintaining of B. alexandrina at low concentrations of NH4C1 [5, 10, 15 and 20 ppm] greatly reduced their survival rate and fecundity. The net reproductive rate was deleteriously affected. This rate was significantly reduced than that of the control snails in all tested snail groups. The reduction in Ro was 86.9%, 90.8%, 93.9% and 96.9%, respectively. The susceptibility of B. alexandrina to infection with S. mansoni and E. Liei miracidia and infectivity of these two parasites were greatly reduced. Increasing the salt concentration increased this reduction. The magnitude of reduction in infection rate was lower in case of E. Liei than that in S. mansoni indicating that E. liei was more tolerant to the effect of this salt than S. mansoni