Abstract
In order to clarify a developmental mechanism of vertebral anomalies, the incidence and the morphology of abnormal vertebrae in juvenile cyprinid fish, Zacco platypus, both wild-caught and laboratory-reared specimens were examined. The frquencies of vertebral anomalies in juvenile fish (8.0-33.0mm in standard length (SL)) collected from the Ibi River were higher than those from either the Yahagi River or the Toki River. In juvenile fish taken from the Ibi River, the frequency of vertebrae joined by abnormal calcium deposits was about 7 times as great as that of helical sutures of centra and about 14 times as great as that of shortened vertebrae.Out of the 4, 564 fish (8.0-19.0mm SL) taken from the Ibi River, 273 (5.98%) specimens had abnormal calcium deposits stained with alizarin red S alongside of vertebral column.In 273 fish having abnormal calcium deposits, 171 (62.6%) specimens showed abnormal calcium deposits extending from one centrum to the next one, and 13 (4.8%) specimens showed them extending to the two adjoining centra.In these defective vertebrae, the separate centra could be distinguished.And the other fish (32.6%) showed the abnormal calcium deposit attaching to a single centrum.The vertebrae joined by abnormal calcium deposits were seen only in fish ranging from 8.0-19.0mm SL;not a single instance of this anomaly has been found in fish ranging from 19.0-25.0mm SL. The frequencies and the incidence of the fused vertebrae throughout the vertebral column in fish ranging from 19.0-25.0mm SL were similar to those of vertebrae joined by abnormal calcium deposits in fish ranging from 8.0-19.0mm SL. These results may suggest that the vertebrae joined by abnormal calcium deposits extending to the adjoining centra in specimens ranging from 8.0-19.0mm SL were fused together during the next period, 19.0-25.0mm SL. Therefore, abnormal calcium deposits extending to the adjoining vertebrae are one cause for fused vertebrae in Zacco platypus. The frequencies of this type of vertebral anomaly in fish taken from the Ibi River were higher than those from either the Yahagi River or the Toki River.
