Heterotrophic bacterial flora of Pmonadon from an apparently healthy hatchery system as well as a pool with heavy mortality were isolated and studied. In the
healthy systems comparatively higher generic diversity with Pseudomonas, Acinetobacter, Bacillus, Micrococcus, members of the family Enterobacteriaceae
and coryneform group in the diminishing order of dominance was recorded. Meanwhile from the moribund larvae and rearing water Aeromonas and Pseudomonas
could be isolated in almost equal proportions. Strikingly, Aeromonas could not be isolated from the apparently healthy larval rearing system and its exclusive
occurrence in the sick culture system in comparatively higher percentage suggested its possible role in the mortality. They were found to be highly halophilic
exhibiting growth at 10% NaCl. On testing their sensitivity to twenty antibiotics, four of them (Streptomycin, Gentamycin, Methamine mandelate and
Cloramphenicol) were found to be effective on all the isolates of Aeromonas and Pseudomonas suggesting their possible application in the hatchery system in
times of emergency. While doing so, Streptomycin would do comparatively better than the others as the minimum inhibitory dose required was comparatively
lower (200ppm) within a period of 24 hours