Distribution of bacteria involved in nitrogen and sulphur cycles in shrimp culture systems of West Bengal, India

Abstract

The bacteria involved in nitrogen and sulphur cycles and physicochemical characteristics of water and sediment in traditional, modified extensive and semi-intensive shrimp culture systems of West Bengal, India were monitored. The physicochemical parameters, except salinity and sediment pH, were observed to be well within the optimum levels recommended for shrimp culture. The levels of ammonia (NH 3; P≤0.05) and nitrite (NO 2 −; P<0.03) differed significantly among systems. The mean heterotroph counts were always close to or above 10 6/ml pond water and 10 6/g sediment. The counts of total heterotrophs and nitrate reducing bacteria (NRB) of the pond water of different culture systems differed significantly ( P<0.01). While the counts of nitrite oxidizing bacteria (NOB; P<0.001), nitrate reducing bacteria ( P<0.01) and sulphate reducing bacteria (SRB; P<0.03) in pond sediment of the three culture systems differed significantly. The mean counts of ammonia oxidizers increased with days of culture (DOC) in traditional and modified extensive systems, but they remained constant in semi-intensive pond sediment. The mean counts of nitrite oxidizers were generally high in water and sediment samples of modified extensive system. The mean sulphur oxidizing bacterial counts of pond water were higher in semi-intensive and modified extensive systems, which generally decreased with increasing DOC. The sulphate reducing bacterial counts of sediment increased with DOC in modified extensive and semi-intensive systems and vice versa in traditional system. The safe levels of ammonia, nitrite and nitrate recorded in the present study clearly showed that the recycling of nitrogen and sulphur is going on actively in shrimp aquaculture systems. The data on the ecology of bacteria involved in nutrient cycling will not only lead to better control of water quality but also application of right kind of bacteria or microbial products in shrimp aquaculture.