The effect of salt composition on the salinity tolerance of mirror carp (Cyprinus carpio L.) during early ontogeny

The effect of brackish water (BW), with the specific ionic composition of t he water in the Aral Sea basin, and that of artificial standard seawater (S W) on sperm activity, egg fertilization, swelling and further development o f the carp (Cyprinus carpio L.) until the stage of active feeding were stud ied. Spermatozoa are able to fertilize eggs up to 9 g/l salinity The fertil ization rate is already extremely low at 6 g/l salinity (13.4% against 98% in control) when the fertilization, swelling and further development take p lace in salinised water. However, the fertilization rate is nearly the same as in the control, even at 7 g/l salinity, when the eggs are transferred t o control water 5 minutes after fertilization. The swelling process is ther efore regarded as the most sensitive stage in the salt tolerance of carp on togeny. The most important result is the fact that BW With high Ca2+ and Mg 2+ content is considerably less toxic than SW. The present study confirms t hat mirror carp from Ahrensburg (Germany) can tolerate approx. 3 to 4 g/l B W and SW without any visible changes during early ontogeny. Based on these results, possible adaptations to salinity in natural wild carp populations must be taken into consideration.