Abstract
Mass mortalities of juvenile abalones belonging to 4 Haliotis species, H. discus discus, H. discus hannai, H. madaka and H. gigantea, often occur in hatcheries from spring to early summer in western Japan. Some mortalities in H. discus discus have been attributed to the disease named amyotrophia. Diseased and healthy juvenile abalones were collected from 8 different public sea-farming centers from 1988 to 1996, as well as experimentally infected juvenile H. discus discus, and were histopathologically examined to determine if the mortalities were associated with amyotrophia.
Moribund H. discus discus showed atrophy of foot muscle, reduced activity to adhere to the substrate, and some of them exhibited a few incisions on the front margin of the shells. In sections abnormal cell masses originated from the nerve tissue, which is the most characteristic histopathological change in amyotrophia, were observed in various organs of H. discus discus, H. discus hannai and H. madaka, but not in H. gigantea. In moribund abalones such abnormal cell masses were extensively produced mainly in nerve trunk and peripheral nerve in the foot muscle. No possible etiological agent was detected by light or electron microscopy even in experimentally infected H. discus discus. These histological findings suggest that most of mass mortalities of H. discus discus, H. discus hannai and H. madaka are attributed to amyotrophia.
