This study was conducted to investigate Brachymystax lenok tsinlingensis spermatozoa cell morphology and ultrastructure through scanning and transmission electron microscopy. Findings revealed that the spermatozoa can be differentiated into three major parts: a spherical head without an acrosome, a short mid-piece, and a long, cylindrical flagellum. The mean length of the spermatozoa was 36.11±2.84μm, with a spherical head length of 2.78±0.31μm. The mean anterior and posterior head widths were 2.20±0.42μm and 2.55±0.53μm, respectively. The nuclear fossa was positioned at the base of the nucleus that contained the anterior portion of flagellum and a centriolar complex (proximal and distal centrioles). The short mid-piece was located laterally to the nucleus and possessed just one spherical mitochondrion with a mean diameter of 0.65±0.14μm. The spermatozoa flagellum was long and cylindrical, and could be separated into two parts: a long main-piece and a short end-piece. The main piece of the flagellum had short irregular side-fins. The axoneme composed the typical '9+2' microtubular doublet structure and was enclosed by the cell membran e. This study confirmed that B. lenok tsinlingensis spermatozoa can be categorized as teleostean "Type I" spermatozoa; 'primitive' or 'ect-aquasperm type' spermatozoa. To the best of the authers knowledge, this was the first study conducted on the morphology and ultrastructure of B. lenok tsinlingensis spermatozoa.

Institute of Hydrobiology Chinese Academy of Sciences Wuhan 430072 China; Key Laboratory of Freshwater Biodiversity Conservation Ministry of Agriculture of China Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences No 8 1st Wudayuan Road Donghu Hi tech Development Zone Wuhan 430223 China; College of Fisheries Huazhong Agricultural University Wuhan 430070 China; Freshwater Fisheries Research Center Chinese Academy of Fisheries Science Wuxi 214081 China

Institute of Hydrobiology Chinese Academy of Sciences Wuhan 430072 China; University of Chinese Academy of Sciences Beijing 100039 China; Key Laboratory of Freshwater Biodiversity Conservation Ministry of Agriculture of China Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences No 8 1st Wudayuan Road Donghu Hi tech Development Zone Wuhan 430223 China

Key Laboratory of Freshwater Biodiversity Conservation Ministry of Agriculture of China Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences No 8 1st Wudayuan Road Donghu Hi tech Development Zone Wuhan 430223 China

Key Laboratory of Freshwater Biodiversity Conservation Ministry of Agriculture of China Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences No 8 1st Wudayuan Road Donghu Hi tech Development Zone Wuhan 430223 China; College of Fisheries Huazhong Agricultural University Wuhan 430070 China

Key Laboratory of Freshwater Biodiversity Conservation Ministry of Agriculture of China Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences No 8 1st Wudayuan Road Donghu Hi tech Development Zone Wuhan 430223 China; University of South Bohemia in České Budějovice Faculty of Fisheries and Protection of Waters South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses Research Institute of Fish Culture and Hydrobiology Zátiší 728 2 389 25 Vodňany Czech Republic

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