Abstract: Objective To explore the optimized method of paraffin serial section and hematoxylin-eosin (HE) staining of the adult zebrafish visceral tissues. Methods After the zebrafish was fixed, the tissues were segmented, and the thoracic/abdominal segment which contains internal organs was stripped of skin and dehydrated by gradient ethanol (dehydration time was optimized to 30 min), transparented by xylene and embedded by paraffin. The tissue was sectioned serially along the body axis, rinsed with warm water after HE staining, and observed under microscope. Results The microscopic observation of heart, liver, spleen, gallbladder, kidney, pancreas, gastrointestinal tract, testis and ovary showed that effects of tissue sectioning and staining were favorable. The sections were intact without collapse or fracture, the anatomical and cytological structure of all organs were clear and complete, the nucleus were neatly blue-stained and the cytoplasm were neatly red-stained. Conclusion With the optimized histopathological method, we were able to obtain high quality histological specimens of the internal organs of adult zebrafish.

Key words: Zebrafish, Visceral tissue, Serial section, Hematoxylin-eosin (HE) staining