Descriptive morpho pathological lesions and surveillance baseline of mesenchymal tumors in some commercially important marine fish species from the Arabian Gulf, Saudi Arabia

Mesenchymal neoplasms in marine teleosts provide valuable insights into individual pathological states; however, interpreting them as indicators of environmental integrity requires considerable caution, and documenting such tumors is essential for monitoring ecosystem stressors. This study aimed to describe several types of mesenchymal tumors in four commercially important fish species caught in the Arabian Gulf in the Eastern Province of Saudi Arabia. During routine veterinary inspections at landing stations and markets in Jubail in 2025, 1,850 fish samples were examined. Samples included Lethrinus nebulosus , Carangoides gymnostethus , Lethrinus lentjan , and Siganus canaliculatus. Gross pathological examinations were conducted, followed by histopathological assessment using hematoxylin and eosin (H&E) and Masson’s trichrome (MT) stains. Ten cases of neoplastic growths were identified, representing an overall observed frequency of 0.54%. Lipomas were diagnosed in L. nebulosus and C. gymnostethus , presenting as well-circumscribed, greasy, white subcutaneous masses composed of well-differentiated adipocytes. Rhabdomyoma was observed in L. lentjan and was characterized by solitary, pedunculated overgrowths of pleomorphic but benign skeletal muscle fibers exhibiting loss of normal myotome polarity. Rhabdomyosarcoma was identified in S. canaliculatus , with malignant features including poorly differentiated myocytes, cellular pleomorphism, hemorrhage, and infiltration into the abdominal cavity with displacement of visceral organs. As tumorigenesis in aquatic organisms are indicators for many environmental pollutants and stress, further studies are required to confirm the potential etiologies of such lesions in this region.