The objective of this study was to describe the morphology and ultrastructure of Acipenser dabryanus spermatozoa using both scanning electron microscope and transmission electron microscopy. The spermatozoon was consisted of an elongated head with a distinct acrosome, nucleus, mid-piece, and a flagellum. The total length of the acrosome, nucleus, and mid-piece was 7.98 ± 0.64 μm and the mean length of flagellum was 55.42 ± 3.46 μm. The mean length of the whole spermatozoon was 63.40 ± 4.11 μm. The acrosome was consisted of eleven posterolateral projections and a sub-acrosome. There were three endonuclear canals in the center of nucleus in a helical arrangement. The mid-piece contained a proximal centriole, distal centriole, several mitochondria, and a cytoplasmic sheath. Axoneme was the main structure of the flagellum, which came from the sytoplasmic canal. Side fins were located around most areas of the flagellum. This description would be useful to supplement the existing knowledge of spermatozoa of the chondrostean fishes. K E Y W O R D SAcipenser dabryanus, acrosome, spermatozoa, ultrastructure

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