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International Journal of Aquaculture 2012, Vol.2, No.6, 29-39
http://ija.sophiapublisher.com
33
water to be conditioned with a healthy community
of microorganisms due to its success in the
postlarvae to juvenile growth period. The bacterial
communities associated with marine and brackish
L.
vannamei
in culture have been shown to change
with environment rather than diet (Luo et al., 2006;
2009) and this result has been reported in fish as
well (Yan et al., 2012). We can infer from these
results that the shrimp in our study would obtain a
similar beneficial microbial community.
Shrimp culture has been shown to alter the pelagic
bacterial community of intensive closed and open
culture systems (Sakami et al., 2008). Therefore,
systems utilizing previously conditioned culture water
may have a potential advantage over those starting
from clean or non-conditioned water in that the initial
establishment phase can be foregone resulting in a
more stable and complex community of heterotrophic
organisms. At the beginning of our sampling period
the bacterial community associated with raceways
managed by FF and ST solids control were
dominated by gram-negative genera. This community
transitioned into equal proportions of gram-positive
and gram-negative organisms by the end of the
grow-out period but transitioned in a polynomial
fashion. Gram-negative bacteria generally represent
r-selected species whilst gram-positive bacteria
represent k-selected or slow-growing species. Fierer et
al (2007) suggest that this delineation is referred to as
copiotrophic/eutrophic or oligotrophic, respectively.
Utilizing previously conditioned water would provide
a possible avenue to maintain a complex culture of
these organisms. Nutrient concentrations, particularly
with respect to different forms of nitrogen
(ammonium, nitrate, urea, and amino acids) tend to
significantly impact the proliferation of bacteria in a
eutrophic system such as an estuary (Middelburg and
Nieuwenhuize, 2000). A complex community of
organisms would therefore increase the ability of the
system to handle greater nitrogen loads and result in a
more efficient system. We did not explicitly test this
idea in our study; however the exemplary growth we
report is indicative of excellent culture conditions and
these conditions are associated with conditioned water.
The re-use of the same water used in the previous
nursery trial along with specially formulated feed
provided by Zeigler Brothers Inc. may have provided
for the immediate establishment or continued
maintenance of a healthy nitrifying microbial
community in the grow-out study. This allowed for
negligible amounts of TAN and NO
2
-N in the culture
water throughout the grow-out study. Typically
nitrification will require many weeks to attain a
steady state in a closed aquaculture system (Sohier
and Bianchi, 1985), however this system maintained
steady state nitrification throughout the growth
period. Very few studies have chose to use the
aquaculture produced communities of bacteria in
pre-conditioned water within enclosed zero exchange
RAS. We believe that this avenue of shrimp culture
deserves increased attention.
The use of an established community of bacteria will
likely prevent the onset of disease through competitive
exclusion or limitation of pathogenic strains. We did
not observe a single case of disease related death
throughout the study. Further, consumers and
aquaculturists have become increasingly aware of the
hazards of dosing intensively produced aquacultured
stocks with antibiotics. Typically, shrimp farmers
utilizing this disease prevention technique have
incurred crop losses frequently in large production
areas such as Thailand (Holmstrom et al., 2003). The
acquisition of antibiotic resistance in potentially
pathogenic bacteria such as
Vibrio
sp. is a typical side
effect of antibiotic overuse (Le et al., 2005; Nakayama
et al., 2006). Further, the use of the antibiotics
oxyteracycline and oxolinic acid has been shown to
decrease the expression of immune-related genes
associated with antibacterial processes in shrimp
(Fagutao et al., 2009). In each of the aforementioned
studies, farming practices were carried-out in pond
systems rather than RAS.
Probiotic strategies have been employed as an
alternative to antibiotics in shrimp aquaculture for
the past 20 years; however most of these studies
have used a single organism to outcompete
pathogenic organisms (Verschuere et al., 2000;
Kuhn et al., 2010). A change in strategy from
individual probiotic cultures to established probiotic
communities may be essential to the future of
super-intensive growth systems and the continued
growth of an environmentally friendly and
biologically secure aquaculture industry.