Acute toxicity of nitrite and ammonia to Daphnia similoides of different developmental stages: using the modified Gaussian model to describe.

To gain an insight into the tolerance of Daphnia to nitrite and ammonia, a modified Gaussian model was used to describe the trends of changes in LC50s of nitrite and ammonia to Daphnia similoides at different developmental stages. LC50s of NO(2)-N and NH(3)-N increased with age before maturation and then decreased at maturation. A modified Gaussian model provided an accurate fit for the changes in LC50s of NO(2)-N and NH(3)-N, in which the parameters have definite biological meanings. From this model, we can gain an insight into the maximum LC50 and the age that has the maximum LC50 and predict LC50s at any specific ages. We suggest that such a model might be used to describe the trend in acute toxicity of some other zooplankton species at different stages.