In order to establish a basis for distinguishing normal and abnormal structures, this paper reports on the growth of vertebral centra in the cyprinid fish, Zacco platypus Temminck et Schlegel.Specimens, 10.0-110.0 mm in standard length (SL), were collected from the Yahagi River, Aichi Prefecture, in August, 1978.Juvenile fish were collected from the Ibi River, Gifu Prefecture in October 1978 and in April 1979.Length and diameter of centra of the 263 specimens were measured for different growth stages, seasons and sexes.
Ossification of vertebrae begins in the postlarval stage, at about 8.0 mm SL.In fish smaller than 16.0 mm SL, all centra are almost equal in length.At 24.0-26.0 mm SL, lengths of centra located at the anterior part of the caudal region are longer than those in the other regions.As the fish grow, growth rate becomes greater in the middle part of the column than the other regions.The diameters of centra in fish of 10.0-16.0 mm SL show no difference associated with the portion of centra through the vertebral column.In fish larger than 24.0 mm SL the diameter of centra located at the anterior part of the column and around the transitional area between the abdominal and caudal region is larger than those in the other regions.In the adult stage, there are no sexual differences in the length and the diameter of centra.
The proportions of vertebral column length to standard length in specimens of 10.0-16.0 mm SL are significantly smaller than those in specimens above 24.0 mm SL.And, there are significant differences on the ratios of total length of centra to column length between the three size-groups, 10.0-11.0 mm SL, 15.0-26.0 mm SL and above 60.0 mm SL (t-test, P<0.001).
The lengths of centra in juvenile fish (15.0-16.0 mm SL, 19.0-20.0 mm SL) collected in April are larger than those in October and August, but the diameters of centra in the former are smaller than those in the latter two months.There is no difference in the length and the diameter of centra between juvenile fish in August and those in October.The ratios of spinal column length to standard length of juvenile fish in April are significantly larger than those in August and in October (t-test, P<0.001).
