Abstract:  Due to environmental pollution and artificial hunting and other factors, the number of wild Rana nigromaculata has been far from meeting the needs of people, hence the artificial training of domesticated Rana nigromaculata is gradually emerging. Nevertheless, to ensure the production of domesticated Rana nigromaculata, the first step is to solve the food intake related problems. The tongue is an important feeding and taste organ, which directly affects its food intake function. In this study, optical microscopy, scanning electron microscopy and transmission electron microscopy were used to study the ultrastructure of the dorsal surface and interior of the tongue of wild and domesticated Rana nigromaculata. The paraffin section study showed that both wild and domesticated Rana nigromaculata had keratinized filamentous papillae and bacteriform papillae. Filamentous papillae were distributed throughout the dorsal surface of the tongue and were composed of primary and secondary papillae. The bacteriform papillae were round, located at the tip of tongue and tongue margin. When the epithelium was removed, the epithelium of the bacteriform papilla was volcanically shaped with a taste bud cavity at the top. However, there were some differences in the histological structure of the tongue: the filamentous papillae on the tongue surface of wild Rana nigromaculata are more developed, and the degree of keratinization was more obvious than that of domesticated Rana nigromaculata. By comparing the ultrastructure of scanning electron microscopy, it was found that both wild and domesticated Rana nigromaculata could be observeed that there were large size circumvallate papilla on the lingual side of the dorsal surface caudal region, and foliated papilla composed of epithelial folds separated by parallel grooves. There were some differences in the scanning submicrostructure of tongue tissue between the two species. The filamentous papillae on the tongue surface of wild Rana nigromaculata were more developed and the degree of keratinization was greater than that of domesticated Rana nigromaculata. This was consistemt with the results of paraffin section study. The comparative observation of ultrastructure by transmission electron microscopy showed that the tongue heart of wild and domesticated Rana nigromaculata was composed of skeletal muscle fibers, connective tissue and tongue glands. The muscle fibers crossed over in three planes. The lamina propria and submucosa contain blood vessels and nerve fibers and were surrounded by thin connective tissue fibers. The salivary glands were confined to the back of the tongue and consist of many serous and mucous cells. Therefore, it can be inferred that the tongue structure is closely related to its food intake. The results of this study not only can enrich the study of tongue histological structure of Rana nigromaculata and amphibians, but also provide experimental basis for the conservation of wild germplasm resources of Rana nigromaculata, the improvement of diet formula of domesticated Rana nigromaculata and the development of industrial production.
Key words: wild Rana nigromaculata; domesticated Rana nigromaculata; lingual papilla; histology; aquaculture
（Acta Laser Biology Sinica, 2022, 31(6): 550-558）