Abstract: To study ecological characteristics of the fish density,this paper compared the spatial-temporal distribution of fish density between the Minjiang Estuary and Xinghua Bay,involved in some impact factors such as dominant species,background of topography and geomorphy,as well as hydrological features,based on the data from four oceanographic censuses in the two kinds of waters during April(spring)and September(summer)2008.Results showed that weight density(165.31 kg/km²)and individual density(15.89×10³ ind/km²)at the Minjiang Estuary,were higher than those(638.4 kg/km² and 19.73×103 ind/km²)at the Xinghua Bay during spring,contrarily in summer,weight density(1 728.83 kg/km²)and individual density(158.81×10³ind/km²)at the Minjiang Estuary,were far higher than those(1 378.20 kg/km² and 58.15×10³ ind/km²)at the Xinghua Bay,which are related to fish resources of the two waters.In the Xinghua Bay,the most dominant species were endemic species with low dominance and contribution to total density except Polynemus sextarius.But in the Minjiang Estuary,the most dominant species were economic migratory species among which Coilia mystus contribute the largest percentage both in weight and in individual densities.The weight density in the Minjiang Estuary was lower than that in the Xinghua Bay in spring because migratory fishes did not arrive at the Minjiang Estuary waters to spawn,but the case was opposite with the migratory fishes arriving at Minjiang Estuary in summer.High density located in southern waters of the Minjiang Estuary where a lot of migratory fishes such as Mugil ophuyseni,Coilia mystus,Harpodon nehereus,Chelidonichthys spinosus and Mugil soiuy while aggregation of migratory fishes(such as Polynemus sextarius and Trachurus japonicus)together with endemic fishes(such as Dasyatis zugei and Johnius belengerii)formed the higher density in head waters than other waters in the Xinghua Bay.