Morphological changes of embryo and yolk sac larvae of barred knifejaw (Oplegnathus fascltus) under salinity stress.

To study the effects of salinity on the development of barred knifejaw(Oplegnathus fascltus)embryo and yolk sac larvae,the fertilized eggs of O.fascltus were put in seawater with different salinity,and their buoyancy,diameter,oil globule diameter,hatching rate,abnormality rate as well as the morphological changes and nutrient utilization of yolk sac larvae were observed.The results indicated that the fertilized eggs subsided in seawater at the salinity of 25 or lower,but floated on the seawater surface at the salinity of 30 or higher.Most embryos were buoyant at salinity 26.The larvae were hatched after 24-30 h in seawater at 22.5 ℃-24.0 ℃,and the hatching time was not significantly affected by salinity(P0.05).Larvae could be hatched at the salinity from 20 to 50,but the hatching rate and abnormality rate were significantly affected by the changes of salinity.The suitable salinity for hatching was from 25 to 35,and the theoretical optimum salinity was from 28.5 to 30.5.Small fertilized eggs were obtained at higher salinity,and the post-embryonic larvae hatched at higher salinity water had the smaller volume of yolk sac.The total length and height of larvae reduced significantly with increasing salinity,whereas the diameter of oil globule was not affected by seawater salinity.