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Production of L. vannamei in recirculating aquaculture systems: management
and design considerations
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2. 1
Production of Litopenaeus vannamei in Recirculating
Aquaculture Systems: Management and Design
Considerations
Peter Van Wyk
Southwest Virginia Aquaculture Research and Extension Center, 424 W. Main St., Saltville, VA 24370
Phone: 276-496-4999; Fax: 276-496-4970; Email: pvanwyk@vt.edu
Introduction
Annual per capita shrimp consumption in the United States is on the rise, increasing from
2.5 to 4.0 pounds from 1995 to 2004 (NMFS Statistics). Most of the shrimp consumed in
the U.S. is imported, and in 2004 alone, shrimp was responsible for a $3.8 billion trade
deficit. Currently, the majority of U.S. shrimp production is from capture fisheries, but
the shrimping industry is in decline due to high fuel prices and declining shrimp stocks.
Aquaculture offers the best hope for increasing domestic production to meet this
increasing demand. Most of the farmed shrimp in the U.S. are produced in coastal ponds
located in Texas, South Carolina, and Hawaii. However, the potential for increasing
coastal pond production is limited by the high cost of coastal land and cold winters (Van
Wyk, et al., 1999). This has led U.S. researchers at several institutions to begin
developing the technology to produce marine shrimp in enclosed, recirculating
aquaculture systems (Davis and Arnold, 1998; Van Wyk, et al., 1999; Samocha et al.,
2001; Moss et al., 2002; Weirich et al., 2002). These systems are attractive to shrimp
producers in the United States because they allow shrimp to be cultured year round
virtually anywhere, facilitating marketing of the shrimp in regional niche markets.
Recirculation technology reduces the water requirements and discharge from the culture
system, minimizing environmental impacts. Another important advantage of indoor
recirculating systems is the high degree of biosecurity that they offer (Ogle & Lotz, 1998;
Moss, 1999). The shrimp species that is best-suited to high intensity inland aquaculture
systems is the Pacific white shrimp, Litopenaeus vannamei. Pacific white shrimp
perform well at high densities (Davis and Arnold, 1998; McNeil, 2000; McAbee, et al.,
2006), and at low salinities (Van Wyk et al., 1999; Samocha et al, 2004).
However, it is becoming increasingly clear that the traditional recirculating aquaculture
technologies used for most finfish species are not appropriate for shrimp culture.
Traditional recirculating aquaculture systems rely on rely on rapid removal of solid
wastes and fixed-film nitrification to maintain water quality. But unlike most of the
commonly cultured finfish species, L. vannamei is a detritivore and is capable of deriving
a significant portion of its nutrition from decomposing organic matter. There is a
growing body of evidence that L. vannamei are not able to realize their full growth
potential in clear water systems lacking significant quantities of organic detritus for the
shrimp to feed upon. Studies conducted at the Oceanic Institute (Leber and Pruder, 1988;
Moss, et al. 1992; Moss, 2002) demonstrated that shrimp maintained in clear water
systems did not grow as well as shrimp maintained in pond water, even when fed high
quality pelleted diets. The faster growth rates of shrimp maintained in pond water were

3. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
2
attributed to the presence of organic detritus and algae suspended in the pond water. In a
later study, Moss (2002) demonstrated that the backwash from a propeller-washed bead
filter significantly enhanced the growth rates of shrimp maintained on a 30% protein feed
in filtered well water. The backwash material was obtained from a bead filter that was
filtering suspended solids from a shrimp raceway and consisted of a mixture of shrimp
feces, uneaten feed, bacteria and protozoans. This study demonstrated that suspended
organic material generated in situ within shrimp raceways has significant nutritional
value for the shrimp and can enhance shrimp growth rates.
In recent years a new zero-exchange pond production strategy has emerged as
aquaculturists have learned that shrimp yields can be increased by promoting the
development of organic flocs in the water column (McIntosh, 1999). This is
accomplished by eliminating water exchange, and aerating intensively (Chamberlain and
Hopkins, 1994; McIntosh, 1999). The organic flocs that develop in these high density,
zero-exchange systems consist primarily of fecal wastes, heterotrophic bacteria, and dead
phytoplankton, and serve as a major source of nutrition for the shrimp (Burford et al.
2003; Burford et al., 2004). The recycling of nutrients through the detrital food chain
increases the protein utilization efficiency by the shrimp, permitting feed protein levels to
be decreased (Burford et al., 2004, Avnimelech, 2004).
Based on these observations, it makes sense that strategies for culturing shrimp in
recirculating system should include a mechanism for developing and maintaining
suspended organic material within the culture tank. This represents a fundamental
departure from the traditional recirculating aquaculture water treatment paradigm. The
objective of this paper is to explore how shrimp recirculating system design and
management criteria differ from traditional recirculating systems.
Management Regimes:
Ammonia is the primary excretion product of protein metabolism and is excreted by
shrimp as unionized ammonia. Unionized ammonia is highly toxic to the shrimp and
must be removed from the system. There are potentially three different pathways for
ammonia removal in a zero-exchange system: 1) nitrification by autotrophic bacteria; 2)
assimilation by heterotrophic bacteria; and, 3) assimilation by photosynthetic algae
(Ebeling, et al. 2005). In any given aquaculture system the types of bacteria and/or algae
that develop and contribute to ammonia removal will be a function of the management
regime. The principle variables that determine the bacterial or algal composition of the
system include: solids removal rate, quantity of surface area provided for nitrifying
bacteria, C:N ratios of the feed, alkalinity of the water, oxygen and light intensity. Some
management regimes will promote the development of hybrid systems in which
significant quantities of ammonia are removed by multiple pathways.
Chemoautotrophic Production Systems:
Recirculating aquaculture systems for finfish are typically designed and managed to
promote the dominance of chemoautotrophic nitrifying bacteria. The buildup of
ammonia-nitrogen is controlled by the nitrification of ammonia-nitrogen to nitrate-
nitrogen by the autotrophic bacteria, Nitrosomonas and Nitrobacter. Biofilters with

4. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
3
sufficient surface area must be provided to support full removal of the quantity of
ammonia-nitrogen that is produced each day. Bicarbonate supplementation is generally
required to replace the alkalinity consumed during nitrification. Solid wastes are rapidly
removed from these systems to prevent the growth of heterotrophic bacteria and the
accumulation of organic carbon. TSS concentrations are typically maintained below 25
mg/L. Light intensities are kept low in chemoautotrophic systems to inhibit algal growth.
In a pure chemoautotrophic system there will be very little organic detritus available to
serve as a supplemental food source for the shrimp, so complete feeds with relatively
high protein levels (35%) must be used. Even when high protein feeds are used, shrimp
growth rates are generally poor in these systems. Gut passage times for L. vannamei
juveniles are only about 60 minutes (Beseres, et al., 2005). In systems where the fecal
wastes do not enter the detrital food chain, protein utilization efficiencies average 15-
25%; in contrast, in systems where a detrital food chain is allowed to develop, protein
utilization efficiencies may be as high as 45% (Avnimelech, 2004). Because of the poor
growth performance of shrimp raised in these systems, pure chemoautotrophic systems
do not appear to be a good choice for shrimp production.
Heterotrophic Production Systems:
Pure heterotrophic production systems are characterized by little or no water exchange,
limited removal of solid wastes, dense microbial flocs suspended in the water column and
low light intensities. In a pure heterotrophic production system there is no need for a
fixed-film biofilter because the ammonia-nitrogen is controlled at very low
concentrations by heterotrophic bacteria. Heterotrophic bacteria require organic sources
of carbon for cellular synthesis. Nitrogen, however, may be obtained either from the
metabolism of proteins and amino acids, or from uptake of inorganic nitrogen in the form
of ammonia-nitrogen or nitrate-nitrogen (Kirchman, 1994). Heterotrophic bacteria will
preferentially utilize organic nitrogen sources when feed C:N ratios are less than 10
(Lancelot and Billen, 1985). Shrimp feeds used in high intensity culture systems
typically contain 35% protein. Assuming the carbon content of 50%, the C:N ratio of a
35% protein diet is only 8.9. In systems fed exclusively with a typical commercial
shrimp diet, heterotrophic bacterial populations will be carbon limited, and little
inorganic nitrogen will be assimilated by the bacteria. Carbohydrate supplementation
allows the bacteria to utilize inorganic nitrogen (Avnimelech, 1999, Ebeling et al., 2005)
which, in turn, permits greater numbers of bacteria to be supported. Carbon:nitrogen
ratios can be increased either by offering feeds with lower protein and higher
carbohydrate contents, or by supplementing the feed with a source of carbohydrate such
as sugar or molasses. Avnimelech (1999) showed that approximately 20 units of
carbohydrate (CHO) are required to remove one unit of ammonia-nitrogen (NH4-N). The
total amount of carbohydrate supplementation required to remove the ammonia-nitrogen
generated from a given amount of feed can be calculated using the following relationship:
kg CHO = kg feed x kg N/kg feed x kg NH4-N /kg N x 20 kg CHO/ kg NH4-N (1)
Assuming there are 0.16 kg N per kg protein in the feed, a 35% protein feed will contain
0.056 kg N/kg of feed. If we also assume that 0.5 kg of NH4-N is excreted per kg N in

5. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
4
the feed, then 0.56 kg of carbohydrate would be needed to remove the ammonia-nitrogen
generated from 1 kg of 35% protein feed.
In a pure heterotrophic system in which all of the ammonia-nitrogen is assimilated into
microbial biomass, the microbial biomass will be proportional to the quantity of
ammonia-nitrogen generated and to the protein content of the feed. This means that the
oxygen demand and carbon dioxide production will also be related to the protein content
of the feed. Reducing the protein content of the feed will reduce energy costs since less
energy will need to be expended on aeration and de-gassing of carbon dioxide. There is
good evidence that the protein content of the feed can be reduced to 30% or perhaps even
less without compromising shrimp growth rates. In heterotrophic systems protein
utilization efficiencies may be nearly double those observed in clear water systems
(Avnimelech, 2004). The improvement in protein utilization efficiencies is due to the
fact that shrimp re-ingest un-assimilated nitrogen in the form of microbial protein and
fecal wastes (Burford et al., 2004). However, lower protein diets may need to be
specially formulated to ensure that other essential nutrients are present in sufficient
quantities.
Heterotrophic systems are often characterized as “zero-exchange” systems. Zero-
exchange implies that no suspended solids should be removed from the system. This is a
misconception. Heterotrophic aquaculture systems are conceptually very similar to
activated sludge systems for wastewater treatment. Sludge age (the residence time of
solid wastes in the system) is a major variable in the management of these systems. As
sludge age increases more complex microorganisms such as flagellates and ciliates grow.
These microorganisms often feed on each other (e.g., ciliates feed on bacteria). When the
microorganisms feed on each other rather than directly on the fecal wastes, BOD is not
consumed, and the energy required to meet the oxygen demand of the microorganisms
remains high (Boehnke, et al., 1997). Thus, for BOD reduction, a high sludge age is
undesirable. Sludge age in wastewater activated sludge systems typically ranges from 10
– 30 days. It is also important to note that extremely large quantities of bacterial
biomass are generated in heterotrophic production systems (Ebeling, et al., 2005). The
doubling time for heterotrophic bacteria is on the order of 2-3 hours. The rapid growth
rates of heterotrophic bacterial populations can lead to very high levels of suspended
solids in the culture tank. In one study of shrimp production in a heterotrophic system,
TSS levels reached as high as 800 mg/L (Ebeling, et al., 2004). High TSS levels are
associated with high BOD, high carbon dioxide concentrations and low pH, making it
difficult to maintain optimal culture conditions for the shrimp. The short bacterial
generation times tend to make heterotrophic production systems very volatile. The
bacterial population can double within hours in response to a feed event, doubling oxygen
demand and carbon dioxide production. If carbon supplementation is interrupted for a
few days, the bacterial population will crash, leading to a spike in ammonia
concentrations. Reducing TSS levels can help reduce the volatility of these systems.
Optimal TSS levels for heterotrophic shrimp production systems have not yet been
established, but it is safe to say that some degree of solids removal is essential for the
maintenance of a stable, healthy culture environment for the shrimp. As we learn more
about managing heterotrophic shrimp production systems it is likely that one of the key

6. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
5
management tools will be the manipulation of sludge wasting rates to maintain optimal
TSS levels in the culture tank.
Photoautotrophic Production Systems:
Many of the studies on shrimp production in recirculating aquaculture systems have been
conducted in greenhouse-enclosed raceways (Van Wyk et al., 1999; Moss, 2002;
Weirich, et al., 2002; Atwood, et al. 2004; Samocha, 2004). Water quality and shrimp
nutrition in these systems are heavily influenced by the presence of photosynthetic algae.
In systems dominated by algae, ammonia-nitrogen and nitrate-nitrogen are controlled by
direct uptake and assimilation into algal biomass. Algae also serve as an important
source of nutrition for the shrimp, (Moss, 2002, Burford, et al., 2004). Algae are a better
source than bacterial biomass for some essential nutrients such as omega-3 fatty acids,
and certain amino acids.
Algal-dominated production systems may experience dramatic diurnal swings in
dissolved oxygen, carbon dioxide, pH, and ammonia. These swings can be stressful to
the shrimp and can lead to system instability. Phytoplankton bloom and crash cycles are
frequently observed in photosynthetic zero-exchange shrimp systems (Moss, 2001;
Burford, et al., 2003). At least one researcher has attempted to overcome this problem
by using to artificial lighting to provide constant illumination (McNeil, 2000). However,
it is not clear whether the increased system stability offsets the higher energy costs
associated with this approach. Solids filtration is another strategy that has been
incorporated into photoautotrophic shrimp production systems in an attempt to minimize
the frequency and severity of phytoplankton crashes (Moss, 2001; Atwood et al., 2004),
though with mixed results. Atwood, et al. (2004) reported that contrary to expectation,
TSS and VSS levels actually increased in some treatments in which solids were being
filtered through bead filters. This was apparently due to fouling of the filter media and
inefficient filtration. An alternative solids filtration technology that is less prone to
fouling, such as microscreen filtration, might provide more consistent control of TSS
levels.
Hybrid Production Systems
In reality, no system is purely chemoautotrophic, heterotrophic, or photoautotrophic.
Low light intensity systems will contain a mix of nitrifying bacteria and heterotrophic
bacteria, while systems with higher illumination levels will contain a mix of
phytoplankton and both classes of bacteria. The composition of the microbial
community will be determined by a variety of factors, including light intensity, C:N ratio
of feed inputs, rate of solids removal, and the amount of surface area available for
colonization by nitrifiers. However, it is possible to manage a system to intentionally
balance the presence of chemoautotrophs, heterotrophs, and photoautotrophs, all at the
same time, or in various combinations.
The design of a chemoautotrophic/heterotrophic (C/H) production system will resemble
that of a traditional chemoautotrophic system. The main elements of the filtration system
include some type of solids filter and a fixed-film biofilter. Bioflocs are allowed to
develop by limiting solids filtration, but carbohydrate supplementation rates are lower

7. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
6
than are used for purely heterotrophic systems. By operating these systems at lower C:N
ratios than are necessary for full heterotrophic control of ammonia-nitrogen (Table 1),
residual concentrations of ammonia-nitrogen are sufficiently high to support the growth
of nitrifying bacteria in the biofilter and on other surfaces within the system. Reducing
the number of heterotrophic bacteria in the system should have the effect of reducing the
overall volatility of the system, making it more stable and easier to manage.
Special attention must be paid to the design of the biofilter in C/H production systems
due to the high TSS levels. Biofilters for these types of systems should be resistant to
fouling. Atwood (2004) found that propeller-washed bead filters experienced significant
fouling when loaded with either Enhanced Nitrification polyethylene beads or Kaldnes
Media. It is likely that the fouling problems were due to the dense packing and lack of
movement of the biofilter media within the bead filter. Aerated moving bed biofilters
loaded with Kaldnes media are relatively resistant to fouling due to the shearing forces
created by the continuous tumbling of the media (Van Wyk et al., 1999). The low head
requirement is another positive attribute associated with this type of biofilter. Trickling
biofilters can also tolerate relatively high TSS levels provided the media selected has a
high void fraction (>90%) and a high hydraulic loading rate (200-250 m3
m-2
day-1
) is
used.
It is also possible to manage a system to develop mixed photoautotrophic/heterotrophic
(P/H) or chemo-/photo-autotrophic/heterotrophic (C/P/H) populations. Most of the
greenhouse-enclosed shrimp production systems that have been reported in the literature
were managed as P/H systems (Moss, 2002, Weirich et al., 2002; Samocha, et al., 2004)
or C/P/H systems (Van Wyk et al., 1999; and Atwood, et al. 2004). The primary factor
distinguishing a C/P/H system from a P/H system is the presence of a fixed-film biofilter.
In both of these types of systems, limited solids removal is practiced to allow
development of the phytoplankton and heterotrophic bacterial populations. The high
nutrient concentrations in ultra-intensive culture systems can lead to very dense algal
blooms. This is undesirable because the blooms will produce wide diurnal swings in D.O.
and pH., and because the algae can out-compete the bacteria for nutrients. Dense algal
blooms are rarely stable, and dense blooms are often followed by rapid crashes. Shading
the production tank with a 70-80% shade cloth will allow algae blooms to develop but
will help limit phytoplankton densities. Solids filtration has also been used as a strategy
to control algae and microbial densities in P/H and C/P/H systems (Moss, 2002; Atwood
et al., 2004).
Temperature control is major issue for greenhouse-enclosed recirculating aquaculture
systems. Optimal growth rates of L. vannamei are obtained when temperatures are
Table 1: Carbohydrate supplementation levels (kg CHO/kg feed) and C:N ratios required for 50%
and full control of ammonia-nitrogen as a function of shrimp feed protein percentage.
% protein Feed C:N Ratio kg CHO/kg feed C:N Ratio kg CHO/kg feed C:N Ratio
35% 8.9 0.28 11.4 0.56 13.9
30% 10.4 0.24 12.9 0.48 15.4
25% 12.5 0.2 15.0 0.4 17.5
(Full Het. NH4-N Control)
(50% Het NH4-N Control)
Shrimp Feed

8. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
7
maintained in the range from 28-32ºC. Maintaining temperatures in this range year
round is very difficult to do in a greenhouse environment due to the low insulating value
of the greenhouse covering. The cost of heating a greenhouse structure with an R-factor
of 1.25 is nearly nine times the cost of heating an insulated frame building of the same
size with an R-factor of 11. The high energy costs associated operating a greenhouse
more than offset the higher initial capital costs associated with insulated frame buildings.
However, it is difficult to provide enough sunlight to sustain phytoplankton inside a well-
insulated insulated building. Double-paned skylights in the roof of an insulated frame
building may be the best choice for those who want phytoplankton as a major element in
the shrimp culture environment.
Aeration and Circulation of Culture Tanks
The amount of oxygen required per unit of feed will generally be higher for a shrimp
recirculating aquaculture system than for a typical chemoautotrophic fish recirculating
system. This is due to the BOD associated with the wastes that are not removed from the
system. The oxygen feed ratio for a heterotrophic zero-exchange shrimp recirculating
system may be 1.0-1.2 kg O2/kg feed. In traditional chemoautotrophic production
systems the system designer must choose whether to meet the oxygen requirements of the
system with diffused aeration or with pure oxygen. In high density shrimp recirculating
systems the choice is between aeration alone, or aeration supplemented with pure oxygen.
In addition to helping meet the oxygen demand of the culture system, a well-designed
aeration system helps to circulate the water in the production tank and to keep the
microbial flocs from settling out of the water column. Accumulations of organic matter
on the floor of the culture tank can quickly become anaerobic and generate toxic
hydrogen sulfide. In addition, the aeration system helps de-gas carbon dioxide. Carbon
dioxide production is very high in systems with well-developed populations of
heterotrophic bacteria, and effective de-gassing is necessary to maintain pH within
acceptable limits for the shrimp. A variety of aeration devices (often in combination)
have been used, including air stones (Van Wyk et al., 1999; Weirich et al., 2002, and
others), diffuser tubing (McNeil, 2000), airlifts (Weirich, et al., 2002), propeller
aspirators (Weirich, et al., 2002), and electric paddlewheels (Van Wyk, unpublished
data). Diffusers can be placed wherever necessary to prevent accumulations of organic
material, which is very helpful. However, oxygen transfer efficiencies are much lower
for diffusers than for most mechanical aeration devices. This is one reason why many
systems feature a combination of aeration devices. McAbee, et al. (2006) reported that
using a combination of conventional aeration and oxygen injection allowed for much
more stable production, higher growth rates, higher survivals, and increased yields.
One factor that has limited the profit potential of indoor shrimp production systems is the
relatively low culture densities that have been achieved. Harvest densities for marine
shrimp in recirculating aquaculture systems rarely exceed 7 kg/m3
, while harvest
densities for fish such as tilapia and hybrid striped bass typically exceed 90 kg/m3
.
Shrimp are benthic animals and do not utilize the water column effectively. Shrimp
production is more limited by bottom area than by water volume. Several studies (Moss
and Moss, 2004; Samocha et al., 2004; McAbee et al., 2006) have demonstrated that
production densities of juvenile shrimp in nursery systems can be significantly increased

9. Van Wyk -- Design and Management Considerations for Shrimp Recirculating Aquaculture Systems
8
by deploying Aquamats®
, a type of vertical substrate, in the nursery tank. Aquamats®
serve not only to enhance the surface area for the shrimp to occupy, but also develop
growths of periphyton that serve as a food source for the shrimp. However, Aquamats®
lose some of their effectiveness in growout systems because larger shrimp do not utilize
vertical substrates to the extent that small juveniles will. An alternative strategy for
increasing the productivity of shrimp recirculating systems might be to increase the
amount of surface area available to the shrimp by deploying horizontal substrates within
the culture tank. Although this strategy would appear to be an obvious solution to the
problem, horizontal substrates can interfere with water circulation patterns in the tank and
cause deposition and accumulation of solid wastes on the floor of the tank. Further
research is needed to determine if there is any merit to this strategy.
Conclusions:
The dietary importance of microbes and detritus for L. vannamei is driving the
development of new management regimes for culturing this species in recirculating
aquaculture systems. The lessons gleaned from zero-exchange intensive shrimp ponds
are being applied in ultra-intensive indoor recirculating aquaculture systems. The idea of
operating a recirculating production system with the intent of promoting, rather than
limiting, the development of heterotrophic bacterial populations, and managing ammonia
without being dependent upon nitrifying bacteria, represents a paradigm shift for
recirculating aquaculture. There is still much to be learned about how to manage and
control these systems to increase system stability and profitability. Studies will need to
be undertaken to determine optimal TSS levels, optimal solids wasting rates, how to
control the composition of the microbial flocs, and how best to control the accumulation
of carbon dioxide and stabilize pH.
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