Abstract: This study was carried out in Wuhan University from April to June in 1982 and 1983. The oxygen consumption during embryonic development of Loach(Paramisgur nus dabryanus sauvage and hybrid of P. dabryanus auvage and Misgurnus anguillicau datus) and Silver carp (Hypophthalmichthys molitrix) was measured with Warburg’s microrespirometer. The results are summarized as follows.1. The quantities of oxygen consumption in different embryonic stages of loach and silver carp increase gradually as the development proceeds. The increasing rate of oxygen consumption in relation to the developmental time is exponential.2. The oxygen consumption curve shows fve peaks which correspond to five em bryonic stages: cell cleavage, gastrula neurula, muscclar contraction and hatching. Among these stages, the embryos of gastrula stage and hatching stage are particularly sensitive to oxygen content of water. If the oxygen content decreases at these two sta ges, the embryos will gradually die. Hence, gastrula and hatching are two critical pe riods to oxygen content in water.3. The tendency of oxygen consumption curve in different embryonic stages of silver carp is nearly the same as that of Misgnrnus anguillicaudatus, but the amount of oxygen consumption of the silver carp is about twice as that of the loach. This diffe rence may be due to the different embryonic size and genetic characteristics of the fi shes.