Neoplastic Bone Lesions in Indian Oil Sardine ( Sardinella longiceps ): Apparent Prevalence, Morphological Diversity and Histopathological Insights

This study provides a detailed pathological characterization of skeletal neoplasms in the Indian oil sardine (Sardinella longiceps) from the southeast coast of India. A total of 237,370 landed fish examined at Parangipettai landing center between 2022 and 2024 formed the surveillance population, among which 721 tumour cases were documented. The overall apparent prevalence of grossly detected tumour cases among landed fish examined was 0.30%, with seasonal values ranging from 0.02% during monsoon to 0.72% during summer. Among the tumour-bearing fish, 136 lesions showed skeletal involvement and constituted the focus of the present study. Grossly, these lesions appeared as firm, irregular bony swellings involving predominantly cranial and fin-associated skeletal regions, with lesion diameters ranging from 1.5 to 14.5 mm. Radiographic examination of skeletal cases demonstrated well-defined radiopaque lesions consistent with mineralized skeletal proliferation. Of the 136 skeletal lesions, 112 were suitable for histopathological examination. Histologically, 97 lesions (86.61%) were classified as compact (ivory) osteoma, 12 (10.71%) as cancellous osteoma, and 3 (2.68%) as chondrosarcoma. Osteomas were characterized by well-differentiated mature lamellar bone without cytological atypia or malignant features, whereas chondrosarcomas exhibited increased cellularity, nuclear atypia, a lobulated chondroid matrix, and focal infiltrative growth within the available sections. Because complete tumour margins and surrounding tissues were not available in all chondrosarcoma cases, the extent of invasion could not be comprehensively assessed. These findings provide baseline pathological evidence of skeletal neoplasia in S. longiceps and support continued pathological surveillance and further investigation into the biological and environmental factors potentially associated with tumour development in wild marine fish.