Distribution of total heterotrophic bacteria (THB) and Vibrio parahaemolyticus in shrimp culture ecosystem

Abstract

The populations of total heterotrophic bacteria (THB) and Vibrio
parahaemolyticus were analysed in modified extensive shrimp (Penaeus
monodon) culture pond, located on the bank of Vellar estuary, Parangipettai,
India, for ten months covering two consecutive culture operations. The microbial
load in water, sediment and culture species was more in the first culture
than the second. The microbial load increased with the days of culture, mainly
due to the organic load in the pond environment, however, physico-chemical
parameters such as salinity, temperature, pH and dissolved oxygen were within
the permissible limits throughout the culture. Sediments had more bacterial
load than water and shrimps. A heavy load of THB (40% vibrios) and V.
parahaemolyticus was observed in the first culture that faced a serious viral
disease problem (white spot disease) and mass mortality at the final stages of
culture. The bacteria might have acted as primary pathogen by facilitating the
entry of viron particles as well as secondary pathogen, leading to mass mortality
of shrimps. Prophylactic measures, regular use of disinfectants and proper
pond bottom management have reduced bacterial load in second disease-free
successful culture operation.