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International Journal of Aquaculture 2012, Vol.2, No.6, 29-39
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30
while allowing for close monitoring of environmental
parameters. Further, implementation of super-intensive
zero exchange microbial dominated RAS in greenhouse
settings resulted in 98% survival and no disease
indicating improved biosecurity while increasing
biomass compared to shrimp grown in clear water
(Wasielesky Jr. et al., 2006). Similar results have been
reported by Ballester et al (2010) with slightly lower
survival (~89%), however the microbial-based
super-intensive systems supported increased shrimp
yield while decreasing operation costs compared to
non-microbial based super-intensive systems. The
results from Wasielesky Jr. et al (2006) and Ballester
et al (2010) suggest that the presence of a complex
community of microorganisms can remove potential
toxicants from the water, promote shrimp growth
through feed supplementation and improve shrimp
health by preventing allochthonous pathogenic organisms
from invading the system through competition.
The utilization of probiotic applications, as defined by
Verschuere et al (2000), to RAS has become recognized
as a beneficial practice to shrimp aquaculture see
review by Ninawe and Selvin, (2009). Generally, a
single or combination of several known cultures
isolated from aquacultured shrimp or water used for
culture is used to inoculate the system. Organisms
from the genus
Vibrio
(Austin et al., 1995; Balcázar et
al., 2007),
Bacillus
(Gómez and Shen, 2008; Li et al.,
2007; Rengipat et al., 2003; Vaseeharan and Ramasay,
2003; Solano and Soto, 2006),
Pseudomonas
(Vijayan
et al., 2006),
Roseobacter
(Sandaa et al., 2003), and
Arthrobacter
(Li et al., 2006) have all been employed
in shrimp aquaculture or display promise as potential
probiotics (reviewed by Ninawe and Selvin, 2009).
These bacteria once established within a RAS aid in
the maintenance of water quality, most often with
respect to nitrification (Kuhn et al., 2010). Further
advantages to bacterial supplementation include
microbial floc as natural food to improve growth
(Burford et al., 2004; El-Haroun et al., 2006), prevention
of pathogen proliferation through competitive exclusion
(Verschuere et al., 2000), and immunostimulation of the
immune system of target organisms (Ganguly et al.,
2010). Although probiotic cultures have proved
beneficial, most organisms rely on a complex
community of microbial flora to grow most efficiently
and aid in immune function. The use of pre-conditioned
(established microbial community) RAS water has yet
to become a common practice in aquaculture because
of the difficulty to maintain and promote a microbial
community which represents the target organism
throughout its commercial growth period to food-size.
The current study assesses the efficacy of fully
established heterotrophically dominated water from a
62-day nursery trial to act as a natural probiotic
community to grow
L. vannamei
juveniles to food-size
in greenhouse-enclosed super-intensive RAS under no
water exchange. Further, we analyze the effectiveness
of settling and foam fractionation to control microbial
and algal communities within the system using flow
cytometry.
1 Results
1.1 Shrimp grow-out period
Biometric comparative analysis of settling tank (ST)
versus foam fractionator (FF) salinity treatments
(30.8 vs. 30.3, respectively) was significantly
different throughout the course of this study. In
addition, although the alkalinity in each of the
raceways was adjusted at least two times per week to
maintain a concentration of 160 mg/L as CaCO
3
, mean
alkalinity in the FF raceway was also significantly
lower than ST raceways containing 124 vs. 129 mg/L
CaCO
3
. Similarly, we observed significant differences
in daily nitrate concentrations in raceways using the
FF method (1 027 vs. 855 NO
3
mg/L or 232 vs. 193 mg/L
NO
3
-N). On the last day of our study, we observed the
FF raceway nitrate concentration at 2 028 NO
3
mg/L
vs. the ST raceway concentration at 1 585 NO
3
-N mg/L.
We speculate that in the bottom of the ST,
denitrification occurred under the anaerobic,
sludge-water interface. The mean alkalinity in the
Total ammonia-nitrogen and nitrite levels in all four
raceways remained very low throughout the study
(>0.5 mg/L). Suspended solids were consistently
maintained between 10 and 30 mL/L, although on Day
43 one raceway reached a concentration of 33 mL/L.
We also maintained TSS concentrations at 400 to
500 mg/L and only observed a spike (790 mg/L) once
in one raceway over the duration of the study. A large
portion of the TSS was in the form of VSS. No signs
of bacterial or viral pathogen infections were found in
any of the shrimp samples sent to Texas Veterinary
Diagnostic Laboratory for analysis. Our results from
this study show that 7.5 kg/m of shrimp biomass can
be sustained with periodic oxygen supplementation