Abstract
To clarify the growth feature and tha structure of hard tissue, we studied the vertebral centrumof rainbow trout Salmo gairdneri, using three specimens (BL: 21.0, 29.0 and 40.0cm). We ex-amined the ratio of centrum length to centrum diameter in each vertebral centrum and obtainedthe vaiue of 0.8-1.0 in most centra. This indicates that the vertebral centra of rainbow trout belong to the so-called equivalent type. The hard tissue was observed by microradiography, with the longitudinal and cross sections (about 100μm)cut through the center of notochordal pore. The microradiograph of thin section of centrurn differentiated serially and changed in pattern, but it is clear to sustain the specific characteristics. In longitudinal sections, the V-shaped part of bone was composed of structure like compact bone through the length of vertebral column. In cross sections, the notochordal pore was enclosed by the radial trabecular bones, the arrange-ment gradually turning toward the posterior centra like paired fans set opposite each other laterally.
