Rare Case of Hypermelanosis or Chromatophore Hyperplasia in Incidental Terapon jarbua (Forsskål, 1775) From a Brackish Water Aquaculture Pond.

Hypermelanosis associated with chromatophore hyperplasia was documented in an incidental specimen of Terapon jarbua (Forsskål, 1775) collected from a semi-intensive brackish-water culture pond used for Asian sea bass (Lates calcarifer) production. Gross examination revealed prominent, irregular, and partially coalescent hypermelanotic patches distributed along the lateral body surface and fins, accompanied by localized skin ulceration, whereas the internal organs appeared macroscopically normal. Radiographic assessment indicated that the lesions were restricted to soft tissues, with no evidence of skeletal involvement. Microscopically, the lesions were characterized by marked disruption of normal chromatophore architecture including extensive melanophore proliferation and alterations in associated chromatophore populations. Histopathological examination showed dense dermal melanin deposition, hypertrophic melanophores and disorganization in the dermal connective tissue framework. Fontana-Masson staining confirmed the presence of actively synthesized melanin within the affected tissues. Transmission electron microscopy further revealed abundant melanosomes at different stages of maturation within melanophores, together with cytoplasmic crowding and peripheral nuclear displacement. Bacteriological screening of skin lesions and internal organs on tryptic soy agar supplemented with 2% NaCl yielded no culturable bacterial growth under the incubation conditions tested. These findings are consistent with localized melanophore hyperplasia affecting the chromatophore system. This case highlights the occurrence of significant pigmentation abnormalities in a non-target species inhabiting aquaculture environments and underscores the importance of continued health surveillance and documentation of unusual phenotypic conditions in brackish-water culture systems.