The study of the genome size is highly significant as it can not only help to instruct the hybridization and breeding program，but also aid to the whole-genome sequencing project of commercial fishes. Chiloscyllium plagiosum，Epinephelus coioides，E. akaara，Pseudosciaena crocea，Bostrichthys sinensis and Scophthalmus maximus，with high market value，are commercially important and popular fishes in China because of their delicious and nutritious meat. In China，E. coioides，P. crocea and S. maximus have been the key of the aquaculture industry over a large scale. Nevertheless，there are still limited data of the genome size despite of many corresponding researches on the heredity，evolution and breeding. In this paper，the genome size （C-value） of these fishes was determined using a flow cytometry technique，and Human （Homo sapiens）lymphocyte （3.50 pg/C） was serving as an internal control. The results showed C-values are 4.91±0.24，1.25±0.04，1.23±0.11，0.76±0.03，0.85±0.04，and 0.65±0.01 for C. plagiosum， E. coioides， E. akaara， P. crocea， B. sinensis and S. maximus，respectively. The results showed that the genome size of the class Chondrichthyes was significantly larger than that of Osteichthyes，and the genome size was found significantly different among these fishes except for E. coioides and E. akaara，which are in the same genus and have an affinity relationship between them. The C-values may be used as a criterion for species identification among these fishes. Base on our results and other data from genome-size database which were measured using the same method and control，the relationship between C-values and evolution status and chromosome amount of the fishes was discussed. Most of the data showed that with the higher evolution status of the fish，the lower C-value is presented. To a certain extent，the result demonstrated that C-value prefers to be more condensed along with the evolution of the genome. However，there are many complex factors which can influence the genome size of the fish. The point of view that the genome size positively correlates to the amount of chromosome is not always correct according to the data. In the present study，the amount of chromosome of P. crocea and B. sinensis are 48 and 46 respectively，while their relative genome sizes are 0.76 pg and 0.85 pg. Furthermore，the result also shows that there is more diversity on the genome size among species existing in original order such as the Chondrichthyes and Acipenseriformes of the Osteichthyes，which may be due to an age long evolution history of this fish. Finally，in order to avoid the disadvantages of poor accuracy and low comparability，we consider that the use of the flow cytometry technique and human lymphocyte as a control should be a more appropriate criterion for genome size determination protocol.