Abstract: By the methods of scanning electron micrograph and immunohistochemistry, this paper studied the distribution of epithelial chloride cells (CC) in Nile tilapia (Oreochromis niloticus) gills and the effects of different salinity (0, 10, 20, and 30) stress on the CC number and morphology. The surface scanning of the gills showed the epithelial chloride cells were distributed close to the interlamellar regions of gill filaments. According to the apical size, the CC could be divided into three subtypes, i.e., subtype Ⅰ (>6.5 μm), subtype Ⅱ (3.2-6.5 μm), and subtype Ⅲ (<3.2 μm). The CC number in the gills at different salinities was in the sequence of salinity 10 < salinity 20 < salinity 0 < salinity 30. When the Nile tilapia transferred to the waters from salinity 0 to salinity 10, the total number of the CC in gills decreased, mainly due to the significant decrease of the subtype Ⅰ cells. The CC number at salinity 20 was higher than that at salinity 10, but the difference was not significant. The CC number at salinity 30 increased significantly with the increase of subtype Ⅲ cells. Immunohistochemical staining further confirmed that at different salinities, the Na⁺-K⁺-ATPase immunoreactive (NKA-IR) cells were all distributed in the interlamellar region of the gill filaments. It was suggested that Nile tilapia could adapt to the salinity change of the environment through changing the quantity and morphological structure of branchial chloride cells, and the subtypes Ⅰ and Ⅲ cells could play a key role for the osmoregulation in the waters with low and high salinity, respectively.

Key words: South China, cold damage of longan, yield loss, risk, assessment.