Abstract
Fertilized eggs of Sepia esculenta and Sepiella maindroni were collected from the wild and the embryonic development of S.esculenta was observed in laboratory.The morphological characters of fertilized eggs and newly hatched larvae between the two species were also compared.The effects of different seawater salinities of 20,25,30 (control),33,36 for S.esculenta and 15,20,25,30 (control),36 for S.maindroni on hatching rate were studied,respectively.Changes in egg fluid osmolality and egg Na+/K+-ATPase activity of S.esculenta and S.maindroni were also measured during the abrupt salinity changes of 192 h,respectively.Hatching rates of fertilized eggs at the same salinity and physiological adaptation to the abrupt salinity changes during 192 h were compared between S.esculenta and S.maindroni.The results showed that organ differentiation happened when embryo was 7-day-old,while organ formation occurred when embryo was 14-day-old for S.esculenta.The incubation period of S.esculenta fertilized egg ranged from 21 d to 22 d at 22-24 ℃ and salinity of 30.Hatching rates of S.esculenta and S.maindroni under control treatment were significantly higher than those under other salinity treatments (P0.01),indicating that salinity of 30 was the suitable hatching salinity for fertilized eggs of the two species.Fluid osmotic pressure of S.esculenta and S.maindroni fertilized egg changed as seawater salinity altered during the abrupt salinity change.The egg fluid osmotic pressure of S.esculenta was equal to the medium osmotic pressure,while the egg fluid osmotic pressure of S.maindroni was 60 mOsm/kg higher than those in the medium.Activities of Na+/K+-ATPase were not found in fertilized eggs of two species.These results indicate that fertilized eggs of two species have little ability in regulating osmotic pressure.However,fertilized egg of S.maindroni can accommodate salinity alteration better than S.esculenta.
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