Abstract: A number of young fish which appear reversal sides andcolourless on the eye side were found frequently in artificial culture of the flat fish(Pseudopleurcnectes yokohame). The perentage of revrersal individuals in the popula-tion varied from 4% to 79.5% and the percentage of colourless individuals from0.2‰ to 10‰. Twenty one specimens of the reversal young fish were dissected andobserved. and the external and internal characteristics, the cross of optical nervesand the position of the internal organs were especially discribed. The divergencies ofthe individuals of normal and reversal in morphogensis and the growth rate werecompared and tho relationship between the frequency of occurrence and the localtemperature, salinity and the quentity of hormon used in hatchery and cultivationwere analysized as well.