prevalence and molecular characteristics of vibrio species in pre ...

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host and effluent from the contaminated farms (Lotz, 1997). Intake water can be
purified by screening and filtering to reduce the formites and carrier organisms. Risk
associated with water can be reduced by application of UV, ozone or chemicals before
use (Perera et al., 2008). A study found that application of alternating low-amperage
electric treatments to effluent sea water to inactivate the V. parahaemolyticus while
generating only low levels of chlorine (Park et al., 2004). This method was able to
overcome the problem of chlorine generation that usually results from treatment with
continuous direct current. Farm equipment, such as aeration, harvest nets, containers,
foot wear and vehicles need to be disinfected using suitable disinfectants such as
sodium hypochlorite, iodophors and sodium chloride. Periodically testing for the
specific diseases can carried out for the early detection and quick response and
prevention of disease outbreaks. Training of farm staff is essential for awareness of
the potential risks and biological principles in biosecurity measures (Perera et al.,
2008).
In Sri Lanka, biosecurity measures are monitored by the National Aquaculture
Development Authority (NAQDA). Screening of brood stock for white spot disease is
carried out before being issued to the farmers. If the farm is infected with a disease,
officers inform farmers to harvest non-infected farms using nets, after that affected
farms disinfected using pesticides to destroy the infected shrimps. Water is released
after 4-7 days in to the sediment areas (Weerakoon, 2007). Sometimes the agency
delays the restocking of the post larvae for the next crop in affected zone. Even
though farmers gain knowledge on biosecurity, economic issues restrict the farmer’s
ability or willingness to invest in biosecurity (Munasinghe et al., 2010).
2.10.1.2 Application of probiotics
The use of probiotics is widely prevalent in the aquaculture, especially in
shrimp culture as a means of controlling diseases and improving water quality without
the use of antibiotics and disinfectants (Ma et al., 2009). A probiotic is defined as a
live microbial agent that prevents pathogens from proliferating in the intestinal tract,
on the superficial structures and in the cultural environment of species and that aid