Ultrastructure of the bullfrog (Lithobates catesbeianus-Shaw, 1802) oviduct in different seasons

The bullfrog (Lithobates catesbeianus) is an exotic animal that adapted perfectly to the climatic conditions of Brazil after introduction in the country. These climatic conditions favor the reproduction and fattening of bullfrogs. However, the development of the bullfrog is significantly reduced in colder regions because low temperatures affect the secretion of gonadotropins and change the sensitivity of the germinal epithelium to gonadotropic hormones. Thus, the temperature and photoperiod are abiotic factors that influence the life cycle of this species, especially with regard to reproduction. Samples from different regions of the oviducts (the infundibulum, magnum, and isthmus) of 9 bullfrogs were collected in the different seasons of the year. The samples were fixed and processed for analysis with scanning and transmission electron microscopy. A comparison of the morphology of the oviducts collected during different seasonal periods suggests that the frogs have greater reproductive potential in the spring due to the development of the structures related to the oviduct, presence of developed cilia, and electron-dense granules. However, seasonal changes were noted in the animal throughout the year in preparation for reproduction during the spring and summer.