2976 strains of heterotrophic bacteria, isolated from the rearing shoal, mainly belonged to 18 genera and some genera of Enterobacteriaceae. Clostridium, Bacillus, Corynebacterium, Photobacterium, Flavobacterium, Pseudomonas and some genera of Enterobacteriaceae were the predominant microflora. The community structure of the heterotrophic bacteria had obvious terrigenous characters and differed greatly in the temporal and spatial distribution. The number of heterotrophic bacteria (HB) ranged from 1.62×103 cfu/g to 2.00×105cfu/g, while the numbers of denitrifying bacteria (DB), ammonifying bacteria (AB) and sulphate reducing bacteria (SRB) ranged from 1.50×104 to 5.00×107cell/g, 9.00×104 to 9.0×107cell/g and 9.00×103 to 4.00×106cell/g respectively. Additionally, statistical analysis indicated that the correlation between the amount of HB and DB, AB was positive, furthermore the dependency between HB and AB was very significant. But the correlation between the amount of SRB and HB was negative.