This study was conducted to evaluate the effect of water pH on embryonic development of grass carp {Ctenopharyngodon
idella). Eggs of grass carp were incubated in different levels of acidic and alkaline water. The general embryonic development was described briefly. Moreover, details were given as to the epiboly stage.The effect of the following pH values was tested: acidic water (4.5, 5.0 and 5.5) and alkaline water (9.5,10.0, and 10.5) on the embryonic evelopment. Acidification and alkalization caused disturbances in cleavage and blastula formation and delay of hatching. At pH 4.5 and 10.5, there were no live eggs in 20h after fertilization. Mortality during the development indicate that the most
sensitive stages were embryos just after fertilization and at hatching period. This study indicates that embryonic development of grass carp was possible within the range of pH 5.5 - 9.5, although at the extreme pH levels, certain disturbances and increased mortality occurred. The changes and anomalies during development might have
caused larva mortality during hatching. Survival of the embryos was calculated during development The percent of hatched eggs was calculated in relation to the number of fertilized eggs. The highest percentages of dead embryos were noticed at the extreme pH (4.5) and pH (10.5). The highest percentage of eyed embryos were recorded at pH (5.5) and pH (lO.O).The quality of the hatched larvae in abnormal levels of pH was worse compared to the control. They
died gradually from the beginning of rearing in neutral water.Light and scanning electron microscopy (SEM) were used to
study the effect of abnormal pH on the development of free neuromasts and structure of the eye. Excessive number of free neuromasts were found on the head region of hatched larvae incubated at alkaline pH. Differentiation of retina was inhibited at the same condition. Acidic pH caused partially delaminated lens epithelium and reduce the number of chromatophores .However, in the view of the results obtained, it can be stated that, even a short-term change of pH (resulting from industrial sewege) may adversely influence fish population, especially if occurs during embryonic development.