Abstract: 【Objective】This study aimed to observe and analyze microstructure and ultrastructure of gill tissue in Hucho bleekeri and enrich its basic biological data， providing reference for elucidating the association between gill structure characteristics and life habits in fishes.【Method】The F₁ generation of artificially bred Hucho bleekeri was used as the research subject. Gill tissue samples were collected and fixed in 4% paraformaldehyde and 3% glutaraldehyde respectively. After paraffin embedding and sectioning， the samples were sequentially subjected to hematoxylin-eosin （HE） staining， Alcian blue-periodic acid Schiff （AB-PAS） staining， Masson staining， and Sirius red staining. The histological morphology， mucous cell types， and distribution and classification of collagen fibers were observed under a light microscope. Meanwhile， the ultrastructure of gill tissue was examined using scanning electron microscopy and transmission electron microscopy.【Result】Hucho bleekeri possessed four pairs of gills. The gill rakers were milky-white， needle-shaped， and sparsely arranged （12-14 rakers）. The gill filaments were bright red and elongated， gradually tapering from the base toward the distal end， with the terminal portion remaining free. The gill arch was primarily composed of cartilaginous tissues and covered by stratified epithelial cells. The gill filament surface was distributed with mucous cells and chloride-secreting cells， with chondrocytes providing central support. The gill lamella consisted of respiratory epithelium and pillar epithelium， and the extended cell bodies of two adjacent pillar cells enclosed the capillary lumen， within which erythrocytes were visible. AB-PAS staining results indicated that mucous cells in gill tissue predominantly secreted neutral mucopolysaccharides （PAS-positive）， accompanied by a small amount of acidic mucopolysaccharides （AB-positive）. Masson staining revealed that collagen fibers were evenly distributed in gill tissue， with a collagen fiber tissue area proportion of 0.21%-0.31% （the mean was 0.27%）， and no typical lesions such as fibrosis were observed. Sirius red staining results showed that type I collagen fibers accounted for 80.00%-90.49%， type Ⅲ collagen fibers accounted for 9.51%-19.20%， and the ratio of type I/type Ⅲ collagen fibers ranged from 4.21 to 9.51. Scanning electron microscopy observation revealed that the gill raker surface was uneven and porous； the epithelial cells of gill arches and filaments possessed dense circular microridges arranged in a fingerprintlike pattern； mucus was found on both gill filament surface and gill lamellae， but the number of pores on gill filament surface exceeded that on the gill lamellae. Transmission electron microscopy observation revealed that the gill lamella was mainly composed of flattened epithelial cells， pillar cells， chloride-secreting cells， macrophages， erythrocytes， endothelial cells， and neutrophils in the vascular lumen. Among these， the chloride-secreting cells had an elongated oval nucleus， with the long diameter at 8.3 μm and short diameter at 5.6 μm approximately， and the cytoplasm had abundant mitochondria and rough endoplasmic reticulum.【Conclusion】The gill tissue structure in Hucho bleekeri is highly adapted to its carnivorous nature and the habitat of high altitude， low temperature， and fast-flowing freshwater. Moreover， the gill tissue of Hucho bleekeri have immune cells such as macrophages and neutrophils， constituting a specific mucosal immune barrier that plays an important role in innate immune system.