Keywords: immunohistochemistry; metastasis; neoplasia; nerve sheath tumor (NST); rainbow trout EN immunohistochemistry metastasis neoplasia nerve sheath tumor (NST) rainbow trout 1875 1878 4 10/14/21 20211101 NES 211101 Neoplasia can be present in fish similarly to mammals, with increasing reports of metastatic disease (Sirri et al., 2021). Immunohistochemistry, metastasis, neoplasia, nerve sheath tumor (NST), rainbow trout Based on the criteria established for the classification of soft tissue tumors in domestic animals (Roccabianca et al., 2020), the neoplasm was consistent with a NST with myxomatous matrix deposition, and a final diagnosis of metastatic myxoid NST (morphologically consistent with myxoid schwannoma) was achieved. Tumors are rarely detected in farmed species with a rapid productive cycle, not allowing neoplasia to develop, while detection rate is higher for adult or aged fish as in the case of ornamental and wild species. [Extracted from the article]