Abstract: The ontogenesis of eight isozymic systems in the developing blunt-snout bream, Megalobrama amblycephala, were analyzed with corresponding morphological changes of embryos.The isozymic patterns of eight isozymic systems. Lactate dehydrogenase (LDH), Malate dehydrogenase (MDH), Glutamate dehydrogenase (GDH), Glucose-6-phosphate dehydrogenase (G6PD), Alcohol dehydrogenase (ADH), Isocitrate dehydrogenase (IDH), Esterase (EST), and alkaline phosphatase (AKP), in the early embryonic stages (0-105 hr after fertilization) and six adult tissues of the fish were determined by vertical starch-gel electrophoresis. Approximately 23 loci that encoded these isozymes were expressed in the embryonic stages and adult tissues. The investigated isozymes may be classified into three types of expression. First, those enzymes constantly present in developing embryos, such as LDH-B4, LDH-A1B3 and EST-5, tended to be ordinarily present in ahnost all adult tissues; secondly, the enzymes that appeared in posterial stages of embryogenesis, were found in particular adult tissues or organs and closely correlated to the morphological or functional differentiation of those tissues or organs, such as LDH-C4 and IDH; the third type was the "embryo-specific" enzymes including EST-1 and E-MDH, which were found free from adult tissues, so that they are considered to be "stage specific". In addition, the changes of the activities between groups of MDH as well as those between MDH and G6PD exhibited certain relationships which probably demonstrated that there was a coordinate controlling system. Being different from results of many fishes, the GDH enzyme pattern of the blunt-snout bream was observed tbrought its embryonic stage, but it had no specificity in the adult tissues. The activity of several essential isozymes in relation to metabolic activities of embryonic development was also discussed. It is clear that the exactness of time-space effect in the gene control system is essential for ensuring normal metabolic activities in the ontogenesis of the blunt-snout bream.