美洲鲥胚胎及仔稚鱼的发育

对美洲鲥(Alosa sapidissima)早期生活史阶段的生长发育特征进行了观察和测量, 描述了胚胎和仔、稚鱼的生长发育特征。美洲鲥受精卵球形、无油球, 为沉性卵, 卵径2.85-3.28 mm。在水温20.3℃-21.9℃孵化条件下, 经过82h 孵化出膜, 根据其胚胎发育过程的形态特征, 胚胎发育分为受精卵、卵裂期、囊胚期、原肠胚期、神经胚期、器官形成期和出膜期7 个发育阶段。美洲鲥初孵仔鱼全长为(8.56±0.36) mm, 其卵黄囊体积为(4.57±0.77) mm3。1 日龄仔鱼脑部发育明显, 口张开, 肛门开通, 胸鳍形成。2 日龄仔鱼卵黄囊体积(0.71±0.23)mm3, 只有刚孵化的15.54%。3 日龄仔鱼经过1d 的混合营养期, 卵黄被完全吸收, 4 日龄仔鱼完全营外源性营养, 卵黄囊的体积(V)随孵化时间(h)的变化方程为V=4.1583e?0.0356h(R2=0.9901)。此后, 背鳍鳍条、尾鳍鳍条、臀鳍鳍条和腹鳍鳍条相继在晚期仔鱼出现, 9 日龄仔鱼尾椎开始弯曲, 21 日龄仔鱼尾椎弯曲完成。27 日龄鱼鳞开始形成, 到33 日龄稚鱼全身披鳞, 个体发育进入幼鱼期, 仔稚鱼期间的生长模型方程为: TL=0.0049D2+0.5091D+9.2578 (R2=0.9885, TL 为全长, D 为日龄)。  

STUDY ON THE DEVELOPMENT OF THE EMBRYO AND LARVA OF AMERICAN SHAD, ALOSA SAPIDISSIMA

The American shad(Alosa sapidissima) is a potential aquaculture species with high economic value just like the Chinese shad(Tenualosa reevesii).The fertilizing eggs of American shad were introduced from West coast of American in 2008 and the observation of morphological development of larva and juvenile of American shad were car-ried on.Under the water temperature of 20.3℃-21.9℃,the duration of hatching lasted 82h,according to the morpho-logical characteristics,the embryonic development of Alosa sapidissima may be divided into 7stages: the fertilized egg stage,the cleavage stage,the blastula stage,the gastrula stage,the neural stage,the organogenesis stage and the hatching stage.The fertilizing egg of Alosa sapidissima was spherical,semibuoyant and no oil globule with diameter of 2.85-3.28 mm.The total length of the newly hatched larva was(8.56±0.36) mm and the volume of the yolk sac was(4.57±0.77) mm3 by using the formula of V=4/3π·R/2·(r/2)2.The mouth and anus opened during 1 day after hatching(DAH),meanwhile the brain began to development and the pectoral fin had formed.The volume of the yolk sac of the 2-day-old larva was(0.71±0.23) mm3,just 15.54% of the newly hatched larva.Larva growth and development depend on the energy of yolk sac from newly hatched larva to 3DAH.Then larva entered a mixed feeding stage,finally the larva exhausted all the yolk sac and undertaken exogenous feeding stage in 4DAH,the relationship between the volume of the yolk sac(V) and the hour after hatching(h) was V=4.1583e0.0356h(R2=0.9901).Then the dorsal fin,caudal fin rays,anal fin rays and pelvic fin rays appeared in the late-stage larva and meanwhile the notochord flexion began on 9DAH.Fin ray of each fin completely developed.The scale occurred on 27DAH,the ontogeny of 33DAH juvenile went into the fingerling stages.The regression equation of the relationship between body total length(TL) and age in days(D) was TL=0.0049D2+0.5091D +9.2578(R2=0.9885).