Juveniles of parrot fish (Oplegnathus fasciatus) were graded and divided into three groups (mean initial size): Small group $(32.9pm3.2;g),$ Large group $(130.1pm12.3;g)$ and Ungraded group $(74.8pm29.8;g).$ Growth and sex ratio were monitored over 3 years. It was concluded that no production advantage was gained by weight grading. There were no differences when the pooled data from the two graded groups were compared with the ungraded group, although mean weight and survival of the large group were continuously higher than those of other groups until the end of rearing period. The highest percentage of males was found in the large group. These results show that males start growing faster than females long before the size grading.