Abstract: The effects of acidic water with addition of Al and Ca on the embryo hatchability, fry survival and juvenile gill ultrastructure of silver carp (Hypophthalmichthys molitrix)were studied under laboratory conditions. All eggs were died at pH4.0 within24 hours. The increase in pHvalue was accompanied by a progressive increase in the hatchability of embryo exposed to pH4.5—6.0 and in the survival of fry with age in day from 5 to 15 exposed to pH4.0—6.0. The addition of 0.5mg Al³⁺/L not only further reduced the hatching of embryo, but also caused decrease in the survival of fry under acidic pH. The addition of 3.0mg Ca²⁺/L significantly increased the hatching of embryo under pH4.5 and 5.0. The added 2.0mg Ca²⁺/Lincreased the survival of fry to a certain extent at pH4.5, especially at pH5.0. The exposure to pH4.5 for 8 hours resulted in a severe damage of gill ultrastructure of juvenile; The addition of 1.0mg Al³⁺/L to pH4.5 water enhanced the syndrome; 5.0mg Ca²⁺/L added obviously mitigated the gill damage by acidic water.

Key words: Acidic water, Aluminium, Calcium, Silver carp, Early development, Fish gill ultrastructure