Development of a heterotrophic bacterial community within a closed prawn aquaculture system

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Abstract
The quantitative and qualitative development of a heterotrophic bacterial community in seawater was studied throughout an experimental rearing of the prawnPenaeus japonicus. The maturation of juvenile prawns had been carried out for 8 months in aerated tanks of seawater without any water renewal. Bacteria (337 strains) were isolated from seawater, which had been sampled at different times. Samples from one of the mussels used to feed the prawns and from the digestive tract of one prawn each supplied 40 more strains. 101 tests were performed on each strain, and cluster analysis showed the existence of 4 different groups containing 95% of the sampled strains. Characteristics of the various samples and groups were described in terms of ecotype diversities, catabolic potentialities, nutritional capacities, and morpho-physiological groups. Until nitrification attained a steady state, the heterotrophic community clearly decreased in number and was composed mostly of auxotrophic bacteria (pseudomonads andMoraxella-Acinetobacter groups). These bacteria needed growth factors and were unable to use amino acids (group B). At the end of the experiment (7 months) the bacteria isolated from the water were vibrios and enterobacteria, as were those isolated from the prawn and the mussel. They clustered together in group A. The number of strains that clustered with those of natural seawater (group E) decreased steadily during the experimental period.