First confirmed case of malignant melanoma in Terapon jarbua from Indian coastal water.

Melanoma is a highly aggressive neoplasm of melanocytes, commonly studied in mammals but rarely documented in wild fish populations. This study reports the first confirmed case of malignant melanoma in Terapon jarbua (Forsskål, 1775) from the Parangipettai landing center on the southeastern coast of India. Gross examination revealed superficial raised, hyperpigmented lesions primarily distributed along the dorsal and lateral body surfaces. Wet mount analysis showed extensive melanization within the dermal layers of the affected tissue. Histological examination identified pleomorphic melanocytes with dense melanin deposition, architectural disruption of the skin, and features consistent with superficially spreading melanoma. Scanning electron microscopy of melanotic lesions revealed significant alterations to the epidermal surface, with rounded or angular projections and sharply defined crevices. Transmission electron microscopy showed classical ultrastructural abnormalities such as pleomorphism, irregular melanosome aggregation, binucleation, cytoplasmic vacuolation, and necrotic cells with compromised plasma membranes. The presence of melanosomes at various maturation stages indicated hyperactive melanogenic activity. This novel discovery points to the importance of regular tumour surveillance and research into environmental stressors as possible causative agents, adding to the small but increasing body of evidence of neoplastic disease in Indian marine ecosystems.