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International Journal of Aquaculture 2012, Vol.2, No.6, 29-39
http://ija.sophiapublisher.com
31
consisting of a mixture of 100% O
2
with ambient air
at a rate of 1.0 L/min for 30 to 60 min after feeding.
As the shrimp biomass exceeded 7.5 kg/m, we
supplemented additional oxygen at a rate of 0.1~0.3 L/min
during conditions in which power outage became
cause for concern. In our zero water exchange study,
management of super-intensive shrimp culture could
not have been done without continual monitoring
using YSI 5200 units, which provided real-time DO
measurements and subsequently allowed us to use
considerably less oxygen than compared to previous
trials. During the final week of grow-out, we
supplemented oxygen continually at a rate of 0.3~0.5 L/min
allowing us to produce quality food-size shrimp with
yields as high as 9.75 kg/m.
1.2 Microbial community
The microorganisms associated with this system were
characterized using FACS over a 1-month period
throughout the middle of the study in order to determine
the effectiveness of this technology as a general bacterial
monitoring technique. Data identifying gram-positive vs.
gram-negative bacteria indicated that the bacterial
community present in all four raceways, foam fractionation
or settling tank mediated, was dominated by gram-positive
microorganisms (Figure 1). Differences in bacterial
community structure were not identified between methods
of particulate control or over the characterization period
(two-wayANOVAp>0.05).
General communities residing within the tanks including
bacteria were characterized and found to consist of
six independent populations based upon two
auto-fluorescence parameters (red and green).
Two-way ANOVA tables for each of the six
community members with respect to treatment and
week are provided. Changes in populations R1, R2,
R3, R4, and R5 all indicated significant effect over
time as well as displaying interactions between month
and particulate control treatment with respect to
populations R1 and R4 (
p
<0.05; Figure 2). Population
R1 and R2 increased in prevalence within the
community with regards to treatments (Figure 2).
Populations R3, R4, and R5 displayed decreasing
trends preceded by a peak occurring during the first 3
weeks (Figure 2). Population R6 was found to be least
concentrated in the community as well as the possessing
the most stable density (
p
>0.05) while population R1 was
Figure 1 Gram-stained bacterial population change determined
with flow cytometry
Note: Characterization of gram-positive and gram-negative
bacteria over a 1-month interval in raceways (RWs) outfitted
with either a foam fractionator (solid line) or settling tank
(dashed line) to control particulates. Lines have been fitted to
the points using a Loess regression. The shaded area represents
a 95% confidences interval for the regression line. Points are
individual measurements from each tank
most prevalent (most likely bacteria due to low
fluorescence and small forward scatter value). These six
populations were further subdivided into three size
categories based upon forward scatter paired with red
fluorescence (this specific fluorescence parameter
appeared to drive population differentiation). Picoplankton
(0.2~2 µm) remained the greatest fraction of the
population accounting for no less than 40% of the
cumulative population at any sampling date and reached
levels as high as 70% (Figure 3). Statistical analysis
indicated no differences between FF or ST mediated
particulate removal across sampling dates or between each
individual population (
p
>0.05).
In order to try to isolate water quality parameters that
influenced the proliferation of microorganisms and
particulate in super-intensive zero exchange systems,
multiple linear regression analysis was performed with
respect to the environmental parameters and flora data.
The simplest linear model describing systems with foam
fractionation as a solids control method included
NO
2
-N, cBOD
5
, NO
3
-N, and turbidity. This model
significantly (
p
<0.05) described 85% of the variability