Abstract: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.
