美洲鲥(Alosa sapidissima)胚胎发育形态学及组织切片观察

Morphological and Histological Observation of the Embryo of American Shad (Alosa sapidissima)

中文关键词: 洲鲥  胚胎发育  形态学  组织学

英文关键词: Alosa sapidissima  Embryonic development  Morphology  Histology

中文摘要:

      通过显微镜及连续切片技术，研究了美洲鲥(Alosa sapidissima)胚胎发育过程中的形态学及组织学特征。结果显示，在孵化温度为(21.0±0.5)℃的条件下，美洲鲥受精卵经过71 h 15 min大量孵化出膜，其胚胎发育阶段主要分为6个时期。受精卵第1–5次卵裂均为经裂，第6次卵裂(64细胞期)，纬裂出现，胚盘被分为外部的包被层和内部的深层细胞两部分。受精6 h 2 min，内外卵黄合胞体层形成。受精7 h 40 min，囊胚腔出现。受精10 h 39 min，胚盘下包30%，胚盾形成；受精14 h 50 min，下包50%，三胚层形成；受精17 h 33 min，下包75%，神经板形成；受精21 h 13 min，下包90%，脑原基、视囊、脊索原基和体节出现；受精24 h 15 min，完全下包，神经胚、听囊、前脑、中脑及后脑出现。受精24 h 55 min，克氏囊形成。受精35 h 44 min，心脏和消化管出现；42 h 50 min肾小管形成；47 h 35 min克氏囊消失；60 h 15 min角膜出现。70 h 15 min，仔鱼大量出膜，初孵仔鱼具有一个大而均质的卵黄囊，上面布有明显的色素。美洲鲥胚胎发生发育的特征与大多数报道的硬骨鱼类类似，但在分化发育的时序上具有较大的差异。

英文摘要:

      American shad (Alosa sapidissima) is an abundant anadromous clupeid that is found along both coasts of the United States and part of South Canada. This fish species has high economical and ecological values. Because of its size, market demand and high economic value, the amount of American shad has quickly increased since it was introduced into China. At present, the species has become an important candidate for aquaculture. However, the study about the embryonic development of A. sapidissima is still lacking. Here we observed the morphological and histological characteristics of the embryonic development using microscope and paraffin sectioning. The results showed that at (21.0±0.5)℃, the hatching occurred at 71 h 15 min after fertilization. The embryogenesis of A. sapidissima was divided into six main stages. The longitudinal fissure was observed from the first to the fifth cleavage; after that the horizontal cleavage was visible at the sixth cleavage (64-cell stage); and then the blastoderm differentiated into the enveloping layer at periphery and the deep cells in the center. At 6 h 2 min after fertilization, the internal syncytium and external syncytium were visible at high stage. At 7 h 40 min, the blastocoel was obvious in the blastula stage. At 10 h 39 min, the embryonic shield formed at 30%-epiboly stage. At 14 h 50 min, the three germ layers differentiated at 50%-epiboly stage. At 17 h 33 min, the neural plate was formed at 75%-epiboly stage. At 21 h 13 min, the brain rudiment, optic capsule, notochord and somite formed at 90%-epiboly period. At 24 h 15 min, the neurula, otic vesicle, forebrain, midbrain and hindbrain were visible at 100%-epiboly period. At 24 h 55 min, Kupffer’s vesicle appeared. At 35 h 44 min, the heart and digestive tube appeared. Pronephric tubule was formed at 42 h 50 min, and Kupffer’s vesicle degenerated at 47 h 35 min after fertilization. The cornea was formed at 42 h 50 min after fertilization. A large number of larvae were spawned from the membrane at 70 h 15 min. The hatching larvae had a large and homogeneous yolk sac with pigment cluster. In conclusion, the embryonic development of A. sapidissima has a similar general pattern but different timing compared to other teleosts.