Metastatic thyroid adenocarcinomas in a captive population of kelp bass, Paralabrax clathratus.

In 1976, a spontaneous outbreak of thyroid adenocarcinoma occurred in a captive population of kelp bass, Paralabrax clathratus. Of 180 adult fish that died over 18 months, more than 100 had thyroid lesions. Nodules varied in size, consisted microscopically of diffusely expansive sheets of thryoid-like follicles, were present in the gill filaments, and projected from the floor of the pharynx into the buccal cavity. Although few of the morphologic criteria for malignancy existed in individual cells, the metastatic nature of the neoplasms was evidenced by the focal presence of follicles within the internal organs of many fish. Local invasiveness to surrounding tissue as well as metastases to distant organs suggested the designation of carcinoma, although some specimens could be classified as simple hyperplasias alone. The tumors may have developed from such hyperplastic tissue, and the etiology was possibly linked to a deterioration of water quality, with the potential presence of single- or multiple-factored carcinogens or goitrogens. This report is the first known documentation of thyroid neoplasia in this species of serranid.