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Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28" C. The effects of three temperatures (23,28,33" C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28" C and the yolk-sac stage at 23.28 and 33" C.Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07+0.03 to 0.40 k0.03 pl Oz egg-' h-';blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 i 0.08,0.44 k 0.07 and 0.63 & 0.13 p10, larva I h ' at 23, 28 and 33" C, respectively; Q,,= 1.93). Acute temperature changes from 28 to 33" C caused significant increases in oxygen uptake by embryos (Q,, = 1.69-3.58) and yolk-sac larvae (Q,,,=2.55). Salinity did not affect metabolic rates.Dry weight ofeggs incubated at 28" C decreased 13% from fertilization to hatching. Incubation temperatures from 23-33" C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q," = 2.25).

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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.