Five kinds of artificial sea water with similar salinity, pH and osmolarity were prepared with different concentrations of calcium and magnesium ions. They were complete sea water, calcium-free sea water, half calcium-free sea water, magnesium-free sea water and half magnesium-free sea water. The fertilized eggs from induced spawnings of grey mullet Mzcgil cephalus, were transferred to these sea waters at two development stages, i.e. before the formation of 2-blastomere stage and at the gastrula stage. Survivals of fertilized egg in different sea waters were checked after several hours incubation, the percentage survival was used as an index of the importance of calcium and magnesium to the embryonic development. The results showed that calcium is indispensable to the embryonic development of mullet egg. Magnesium, however, is not the necessary element in the incubation medium.
Salinity tolerance of fertilized eggs and larval survival of the fish Sillago siharna (Forskbl) were compared using fertilized eggs from induced and natural spawnings, and eggs from adults acclimated to lower salinities. Fertilized eggs at the blastomere stage were more sensitive to salinity change than those at other development stages. Fertilized eggs from natural spawning were more tolerant to salinity change than those from induced spawning. Fertilized eggs from adults acclimated to lower salinities showed increased tolerance to lower salinities. Larvae survived longer in lower than in higher salinities.
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