The tonguefish Cynoglossus semilaevis (Günther) is a rare fish species in Chinese offing, inhabiting in the warm water bottom. The metaphase chromosome preparation of the fries has been got from their fins by hot air drying methods, while the metaphase chromosomes of one year old young fish which has physiologically sex differentiation has been got from their renal tissues by the method of PHA and colchicine injection. The karyotypes were examined. The result shows that there are 42 acrocentric chromosomes in diploid and their karyotype formula is 2n=42t, and there existed heterotypic sex chromosome which belongs to ZW/ZZ type. The sex ratio in artificial bred stock is nearly 1∶1.
