Bacterial community composition of sediments from a milkfish Chanos chanos Forsskål farm

Bacterial communities in sediments underneath milkfish cages and adjacent off-cage areas in Bolinao, Lingayen Gulf, West Philippine Sea were characterized using PCR-denaturing gradient gel electrophoresis to assess influence of the fish farming to the sediments. The sediments in the fish cage (FC) area showed anoxic conditions [redox potential of −165 to −213 mV and acid-volatile sulphide-sulphur (AVS-S) of 0.55–1.88 mg g−1 (dry weight)] compared to the relatively oxic off-cage area [redox potential of 72–81 mV and AVS-S of 0.09–0.14 mg g−1 (dry weight)]. The composition of the microbial populations revealed influence of the fish feed sedimentation with higher dominance of putative sulphate-reducing bacteria (SRB) in the FC area. Compositions of the bacterial taxa showed dominance of the Bacteroidetes group and Deltaproteobacteria. The results suggest that the fish feeds created a new suitable environment, in which reductive microorganisms such as SRB, ferric-ion-reducing bacteria and nitrate-reducing bacteria can thrive. Organic load from the feed and quantity of its leftover constituents may be the key factors that influence the structure of the bacterial community in the sediments of the milkfish farms.