Nutrient budgets in intensive shrimp ponds: Implications for Sustainability

Aquaculture 164 1998 117–133
Nutrient budgets in intensive shrimp ponds: implications for sustainability
Simon J. Funge-Smith ), Matthew R.P. Briggs
( ) Stirling Aquaculture Asia , P.O. Box 32, Kao Seng, Songkhla 90001, Thailand

Abstract
Serious production losses have occurred in shrimp producing countries around the world,
principally due to poor rearing environments and pathogenic disease. In response to this, shrimp
farmers are changing their culture methods. To understand the source and sink of nutrients which
affect pondwater quality and effluent impact, the nitrogen, phosphorus and solids budget have
been constructed for water exchange systems. These budgets reveal the contribution of the pond
bottom soil to the accumulation of sediment and phosphorus and its potential contribution of
nitrogen to the pond system. A survey of shrimp farm water quality and management practices in
southern Thailand has also been completed. This reveals a high proportion of farms using low
water exchange methods of shrimp culture but without the ability to maintain suitable water
quality in the production ponds. Shrimp production in these systems is variable due to high
incidences of disease and slow growth rates. The pond processes that might cause this are
suggested and potential methods for their amelioration are discussed. Alternative culture systems
such as lined ponds, low salinity rearing and recirculation farms are described in relation to their
potential for remediating problems within the shrimp culture industry. q1998 Elsevier Science
B.V. All rights reserved. click here to print
Keywords: Shrimp; Production systems; Solids and nutrient budgets

1. Introduction
The rapid increase in world cultured shrimp production and its equally rapid decline in some
countries like Ecuador, China and Indonesia Shrimp News International, 199
has left environmental, social and financial problems in its wake. This has not prevented
) Corresponding author. Tel.: q66-74-324-475; fax: q66-74-324-475; e-mail:
aquacon@t-rex.hatyai.inet.co.th .
0044-8486r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.

PII S0044-8486 98 00181-1
( ) S.J. Funge-Smith, M.R.P. Briggsr Aquaculture 164 1998 117–133 118
the development of new stretches of coastline for shrimp culture and the further
intensification of existing areas. Shrimp farming has the capacity to dramatically
transform coastal areas. Extensive farms have an enormous requirement for land and the
development of intensive culture practices increases nutrient impacts on the local coastal
environment. Alongside environmental changes such as eutrophication, salination and
land use changes, are attendant social transformations Lin, 1989; Chua et al., 1989;
Csavas, 1993; Liao, 1990; Macintosh and Phillips, 1992; Panvisavas et al., 1991;
Primavera, 1991, 1992, 1993, 1995 . These can be both positive and negative; the
increased income into traditionally poor coastal areas must be balanced against loss of
job diversity, loss of independence, rising prices and growing inequity between farmers
and non-farmers Chong, 1990; Masae and Rakkheaw, 1992; Nuruzzaman, 1996; Primavera, 1993,1995 .
Once changes have occurred frequently irreversibly , it is often important to
maintain the industry in some form. Collapse of shrimp farms leaves nothing for the
inhabitants of an area since agricultural land and mangroves are degraded and often,
former farmers are left with considerable debt. This leads to loss of land and an inability
to return to their original lifestyle. There is a pressing need for the development and
dissemination of a range of shrimp culture systems that are both environmentally and
economically sustainable.
Typically the pattern of production from a shrimp farm is that of an initial
‘honeymoon period,’ characterized by success and good production followed by gradual
decrease in yields over successive crops. Depending upon a wide range of factors,
decreased yields are manifested as reduced growth, higher FCR, and disease outbreaks
that require emergency harvesting. The worst case is that of complete mortality of stock
and this is being encountered more frequently with the increasing incidence of extremely
pathogenic viral diseases . Although there are now several primary pathogens viral of shrimp,
the majority of shrimp disease is caused by secondary pathogens that are able to invade shrimp
already stressed and weakened by a poor quality rearing environment. A shrimp that is stressed
does not grow rapidly, principally due to reduced feeding and delayed moulting. It is
important to maintain a healthy rearing environment for the shrimp to maximize
production potential and minimize the risk of opportunistic disease.
The viral type diseases such as ‘yellowhead’ YBV and ‘white spot’ SEMBV
disease appear to be transmitted via influent water and intermediate crustacean host,
respectively. There is now some evidence that ‘white spot’ can also be transmitted
through the post-larvae Flegel et al., 1996 . These diseases cannot necessarily be
prevented by the provision of a good quality rearing environment, although a poor
environment certainly will increase susceptibility. Yellowhead disease already appears to
be decreasing in pathogenicity from that of a primary to opportunist type pathogen. In
1993, only 0.05% of the tiger shrimp Penaeus monodon carrying the virus were
asymptomatic, now this figure has increased to 60% Flegel et al., 1996 . Therefore,
environmental quality will have a more significant effect than before. The response of
Thai farmers to these two viral diseases, has been to reduce water exchange in an
attempt to prevent transmission between farms and ponds. This practice has generated its
own problems which will be discussed later.
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 119
In order to better understand the link between environmental quality and production,
it is important to understand some of the underlying relationships between the two. This
knowledge allows the significant processes occurring in different culture systems to be
identified and suitable management strategies to be derived. click here to print

2. Environmental processes in shrimp culture systems with water exchange
The two significant components of the pond environment are the pond water and
sediments which interact continuously to influence the culture environment. Pond
sediments can be further divided into the pond soil component the pond bottom and
walls and the accumulated sediment component the sludge that accumulates on the pond bottom
during culture Briggs and Funge-Smith, 1994 . Pond management activities are a third external factor
which influence the culture environment.
Management activities include feeding, use of aerators, water exchange and liming Fig. 1 .
The original method of intensive shrimp culture in Thailand involved relatively high y2.
y1 y 1. stocking densities 50–100 m , high production 6–12 t ha crop , high feeding
rates FCR 1.8–)2.0 and high rates of water exchange up to 5–10% per day towards
harvest time . Water quality management was achieved by a combination of flushing the
pond with clean seawater and management of the phytoplankton bloom by assessment of
pond colour. Water exchanges were frequent, especially in the latter half of production.
Accumulated sediment was known to be undesirable and was removed between cycles.
Experience has taught farmers that inadequate sediment removal would cause water
quality problems early in the subsequent crop. Due to the high flushing rates and
naturally high levels in seawater, the alkalinity of the pondwater was not considered
important and no attempt was made to control pH. Oxygenation of the pond during the
Fig. 1. Water quality interactions and management activities in intensive shrimp ponds.
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 120
day was largely achieved by the phytoplankton bloom giving rise to supersaturated
oxygen 130–150% and high pH 8.3–9.5 by the afternoon. This oxygen concentration
would gradually diminish overnight and aeration would be started during the very early
morning to prevent critically low levels. Aeration was usually suspended during the day
to save power costs and in the belief that it was unnecessary. Feed management in Thai
intensive ponds is achieved through the use of lift trays which are checked regularly to
assess if shrimp are feeding. On larger farms, shrimp growth was recorded to cross
check the feeding rates and also to estimate potential production. click here to print

3. Nutrient and solids budgets
A study of this ‘open’ type system was performed in southern Thailand using shrimp
ponds constructed on clay soils Briggs and Funge-Smith, 1994 . Budgets were derived
for solids, particulate organic matter, nitrogen, and phosphorus. Three different types
of pond were investigated: one-year and two-year old ponds stocking density 50–60 m and
one-year old ponds with higher stocking density 80–100 m .The solids budget Fig. 2 shows
that erosion of pond soil was the major source of both solids 88–93% and organic matter 40–60% in the pond.
The feed applied to the pond was a significant source of organic matter 31–50% but contributed little solids
4–7% to the system. This is important since the feed component is also an indication
Fig. 2. Total and organic solids budgets for intensive Thai shrimp ponds Funge-Smith and Briggs,
unpublished data .
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 121
of the faecal contribution by the shrimp. Influent water is a major source of sediments in
extensive systems Boyd, 1992 , but contributes only 2–3% of solids in intensive
systems because stirring generates more endogenous solids. The organic contribution of
the influent water was significant 7–13% , but less so than feed and soil erosion.
Shrimp culture ponds are effective sedimentation areas Boyd, 1992 such that the bulk
of the solids introduced to the system endogenously and allocthonously remain in the
pond as accumulated sediment 91–94% . This accumulated sediment was the sink for
58–70% of the organic matter in the system. Routine water exchange accounted for 4%
of solids discharge and pond drainage for a further 3%. The organic content of these
discharged solids were 13% and 9% respectively. The shrimp were a relatively minor
component in the whole system, accounting for just 0.7% of the solids and 6.1% of
organic matter. The important consideration that emerges from these budgets
is that the character of the pond soil will have a significant effect on the water quality and production of a
shrimp pond. Depending upon initial compaction and organic content, the soil will affect
the organic matter and solids of the system. In the case of mangrove soils, organic
content can be two or three times that of clay soils e.g., rice paddy . Sandy soils are the
opposite containing little organic matter. It is frequently observed that starting phytoplankton
blooms in these ponds is difficult and they are liable to crash frequently. Ponds
with sandy soils also suffer from high seepage rates causing problems as organic
material is drawn into the soil matrix where anaerobic decomposition can occur. After
one or two crops, production losses occur due to seriously deteriorated pond bottom
conditions Funge-Smith and Stewart, 1996 .
The organic component of the accumulated sediment is a mixture of pond soil
organic content and detrital material. This detrital material is composed of sedimented
organic material from plankton, shrimp faeces and uneaten feed. The character of the
accumulated sediment is therefore dependent upon culture intensity, pond soil organic
content, and water exchange practices. Problems associated with the pond bottom and
accumulated sediment occur when excessive organic material builds up causing release
of ammonia, organic sulphur compounds, and, in cases of extremely high organic matter
and acidic soils, hydrogen sulphide Avnimelech, 1996; Lin, 1989; Fast and Lannan, 1992;
Wang and Fast, 1992 .
Inadequate cleaning of the pond bottom between crops leaves organically enriched
sediment across the pond bottom. Due to its non-compacted nature, this sediment is
easily suspended by the action of aerators during the next production cycle. The organic
matter released from this sediment tends to stimulate very heavy phytoplankton blooms
in the first month of production. Because of this, old ponds in Thailand are rarely
fertilized to stimulate phytoplankton bloom. Non-removal and respreading of the
accumulated sediment over the pond bottom has been proposed since the increase in
organic content can be slight. However, experience of poorly cleaned intensive ponds
suggests this is unwise. Non-removal of sediment might be a viable alternative if ponds
were farmed less intensively, fallowed for longer periods, and the sediment compacted.
The solids discharged from the ponds form a minor but significant part of total solids
in the system. The total discharge of organic matter in the effluent was 4.8 t hay1 and
the total solids approximately 12.6 t hay1. Trapping these solids as they are discharged
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 122
represents a major problem in reducing shrimp farm impact on the surrounding
environment. The suspended solids in a shrimp pond have a different character from the
sedimentable solids. Frequent cessation of aeration during the production cycle allows
the heavier soil particles to settle and form the accumulated sediment. Phytoplankton,
bacteria and the organic particulate fraction are not easily sedimented due to natural
buoyancy, or having a specific gravity close to that of seawater Rubel and Hager,
1979 . In trials on shrimp pond waters one hour settlement achieved 22–44% settlement
of suspended solids. There was no significant difference between settling times of 1, 2
and 3 h Fig. 3 . Thus, the use of settling ponds for removal of this fraction is bound to
be ineffective unless enhanced sedimentation is practiced e.g., flocculation . Harvest
effluents are more easily settled because they are a mixture of resuspended accumulated
sediment and the suspended solid fraction of the water.
The actual amount of nutrients assimilated into shrimp biomass is a small fraction of
the total applied as feed Table 1 . Only 18–27% of nitrogen and 6–11% of carbon
applied to the pond was assimilated thus there is considerable wastage as nutrients are
either incorporated into plankton biomass, volatilized or trapped in the sediments.
The nitrogen and phosphorus budgets reveal in more detail, the sources and sinks of
the organic components in an intensive shrimp pond Fig. 4 Fig. 5 Briggs and. Funge-Smith, 1994 .
Applied feed accounted for 78% of the input of N to the ponds Fig. 4 . Erosion of the pond soils,
whilst a major contributor of solids, accounted for only 16% of N added to the system.
Other minor contributions were influent water 4% and fertilizer, rainfall and postlarvae 2% .
The sinks for nitrogen were the sediments 24% , harvested shrimp 18% , and discharged water 27% . This leaves approximately Fig. 3. Settlement of suspended solids from shrimp pond waters
Funge-Smith and Briggs, unpublished data. ( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 123

Composition of shrimp and feed showing assimilation and loss to environment Funge-Smith and Stewart,.
1996 a Nutrient Proximate analysis % dry weight, Composition Assimilation at FCR 1.65–2.40
of 1 kg dry Feed Shrimp grams % y1 feed g kg y1 kg non-assimilated .
A 1 kg of dry feed at FCR 1.65–2.40 produces 113–165 g dry weight shrimp .
30% of the nitrogen unaccounted for which is assumed to be N lost to the atmosphere as
N or ammonia. This volatilization of nitrogen emphasizes the significance of microbial 2
decomposition processes in ponds, especially bacterial conversion of nitrogen com-
pounds principally nitrate to N Fry, 1987 . The high loading of nitrogen in the pond 2
effluent highlights its potential impact on receiving waters. This loss of nitrogen is also a
Nitrogen budget for Thai intensive shrimp ponds using water exchange adapted from Briggs and Funge-Smith,
1994 .( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 124

Phosphorus budget for Thai intensive shrimp ponds using water exchange adapted from
Briggs an Funge-Smith, 1994 wasted resource that could be incorporated into the growth of other organisms.
The site of this bacterial activity is unknown—does nitrate conversion occur principally in the sediments or in anaerobic microzones in the suspended solids fraction? This question is
of considerable importance in the management of bacterial flora in shrimp ponds.
The principal source of phosphorus in this system was the applied feed 51% Fig. 5 .
The 26% shortfall in inputs was assumed to be the eroded pond bottom. None of
these ponds were new and previous cleaning had left old uncompacted sediment on the
surface, which is easily eroded during the next cycle contributing phosphorus to the
system. Effluent water still constituted 10% of P loss in the budget and this is mostly
bound in the suspended solid fraction. Again, trapping of the suspended solid fraction is
important to minimize impact. click here to print

4. Potential solutions
Common problems in the open water exchange system include phytoplankton crashes,
deteriorated pond bottoms and bacterial diseases. A phytoplankton crash causes a
significant increase in ammonia in the water, a decrease in dissolved oxygen and a rise
in organic material. This stressful situation, together with increased bacterial concentrations,
often leads to outbreaks of vibriosis, Zoothamnion infections, and luminescent
Vibrio in the ponds. Traditionally, the only method for ameliorating this problem was
high levels of water exchange Chanratchakool et al., 1995 .
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 125

Monthly water exchange rate % in open, semi-closed and closed shrimp production systems
in southern Thailand 1993–1995 a b c Month Ranod–Hua Sai 1993 Chantaburi 1994
Southern Thailand 1994–1995. NACA 1994 .b Marsden 1994 . c Funge-Smith, 1996.
Due to deterioration of estuarine and coastal water bodies, many shrimp culture areas
no longer have the clean seawater required for this method of culture. This has led to
decreasing amounts of water exchange. One reason for the widescale adoption of low
water exchange systems in Thailand has been the perception that water exchange
triggered disease outbreaks. There is now substantial evidence that the viral disease
yellowhead is transmissible in water and that white spot disease is introduced via
crustacean intermediates during water exchange. The assumption that separating the
production pond from external water inputs may prevent the introduction of viral disease
has given rise to the ‘closed’ and ‘semi-closed’ culture systems in Thailand. click here to print

4.1. Closed and semi-closed systems
These systems operate by filling a pond and using a biocide to kill any potential
vectors of viral disease mysid shrimp, white shrimp, swimming crabs, zooplankton.
The usual biocide used is calcium hypochlorite 60% wrw applied at 300 kg ha , but there
is increasing interest in the use of more specific organo-phosphate pesticides due to the
effect of chlorine on the phytoplankton as well. After chlorination the pond is limed and
aerated to disperse residual chlorine and stimulate the development of phytoplankton bloom.
There is no water exchange in the first two months after stocking in these systems,
although filling of the pond is necessary towards the end of the second month. Depending upon
season and rainfall, evaporative loss can cause salinity to rise to an
unacceptably high level. To counteract this, freshwater is pumped where available
although this has very serious environmental and social impacts if aquifer water is used
Liao, 1990; Primavera, 1991; Csavas, 1993 . During the monsoon seasons, rainfall is
sufficient to prevent high salinities. In the semi-closed system, limited water exchange
commences during the second month of production. In the fully closed system, the
farmers attempt not to change any water at all and merely add water if necessary. Total
effluent loadings from systems employing any form of water exchange are not significantly
different when compared with fully closed systems. The loadings in Table 3
represent those discharged as a result of water exchange, and do not account for
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 126
Nutrient loadings as a result of water exchange activities Funge-Smith, 1996 .

Organic suspended solids accumulated within the system. In the case of fully closed systems,
impacts are relatively small with respect to effluents, but the actual rearing environment is stressful
as a result of high organic loadings within the ponds.
Low water exchange systems such as these are complete sinks for nutrients and thus
there is no outlet for wastes during production except for discharge at harvest Table 3 .
The nitrogen budget above shows that even in an open system water exchange does not
result to a major loss of N 17% Fig. 4 . The lack of water exchange has one
significant management problem, over-blooming phytoplankton. This has always been a
problem since the phytoplankton eventually crashes and causes severe stress to the
shrimp. One of the management methods currently employed is the killing of the bloom
by the application of biocides usually BKC, formalin, glutaraldehyde, calcium hypochlorite .
This is applied in the corners where phytoplankton density is greatest.
Aeration is suspended during treatment followed by vigorous aeration to disperse the
chemicals and reduce the concentration to a harmless level. The dead phytoplankton
releases a great deal of ammonia and decomposes, forming a thick stable foam on the
surface of the pond or sinks to be incorporated into the sediment. The floating foam is
removed from the corners of the pond where it collects.
By virtue of their higher organic loadings, closed and semi-closed systems appear to
encourage dinoflagellate and blue–green algae cyanobacteria blooms e.g., Gymno-dinium,
Peridinium, Gonyaulax, Coscinodiscus, Anabena, Oscillatoria . The dark brown,
red or purple–black appearance of a pond is typical of such blooms and are considered
to be stressful to the shrimp and undesirable in shrimp ponds.
Due to the high concentrations of ammonia often encountered in these two systems,
3.0 mg l , it is vital to control of pH. Daily pH checks are often performed and an
attempt is made to maintain pH between 7.8 and 8.4 during the day time. Alkalinity
phenolphthalein method is also checked regularly. If alkalinity is considered too low
dolomite is applied. If pH rises too high during the day some attempt is made to reduce
the phytoplankton concentration. If alkalinity is too high, organic acids such as acetic
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 127
acid are sometimes added to neutralize some of the carbonate. The requirement for CO2
as a nutrient by the phytoplankton is well known, but the loss of bicarbonate as a result
of acidification due to bacterial denitrification is rarely considered. From the nitrogen
budget approximately 30% of nitrogen appeared to leave the pond in gaseous
form, therefore the bacterial activity required to achieve this must be considerable. Due
to their low solubility, the addition of lime and dolomites to increase buffering capacity
of pond water may not always be effective in controlling water buffering capacity.
Use of formalin has increased significantly due to its biocidal effect, acidity, and
capacity to combine with ammonia. Treatment of ponds with 10 ppm formalin not only
kills phytoplankton when applied, but removes ammonia when dispersed. Formalin also
contains formic acid so that pH is not elevated during treatment. The use of BKC in this
respect has declined because of its high pH Chalor Limsuwan, Department of Fisheries,
Thailand, personal comm. The use of bacterial remediation treatments is also
in these systems in the belief that regular addition will help maintain low ammonia concentrations,
reduce organic matter concentration, and improve the quality of accumulated sediment in the
pond. Since monitoring of these two parameters is rarely performed, there is little
evidence of any effect Funge-Smith and Stewart, 1996 . The addition of carbon sources
to production ponds has yielded interesting results in terms of modification of microbial
communities in ponds. Additional carbon sources sugar, molasses, cane sugar, etc.
appear to increase activity of heterotrophic bacteria in ammonia removal, but in what
form the ammonia is removed and whether this removal is sustained are unknown.
Ideally ammonia would be de-nitrified to nitrate, subsequently converted to nitrogen and
volatilized. This function is not performed by the bacteria usually present in bacterial
remediation products. It appears that if sugar is not applied regularly the bacterial
community is not sustained and ammonia can re-appear i.e., a bacterial bloom crash .
Applications of sugar are approximately 3–5 kg hay1 per time and this may last for
several days to a week. The carrying capacity of a closed or semi-closed system appears
to be exceeded at approximately 100–120 days post stocking resulting in stressful conditions,
slow growth and disease outbreaks. Growth rates are slower in closed systems than open, with
harvest sizes of approximately 40–50 pieces. Harvesting is usually done when
shrimp stop feeding or when farmers perceive that the shrimp are no longer growing.
The slower growth rates and eventual overloading of the closed and semi-closed systems
can be attributed to several causes. The build up of waste sediment releases increasing
amounts of ammonia and organic matter. This in turn encourages heavy Vibrio and
Zoothamnium numbers in the pond. The shrimp become stressed and therefore become
more susceptible to these opportunist diseases. Phytoplankton bloom crashes are frequent
in these systems and, whilst re-blooming is comparatively quick, there is still a
period of stress to the shrimp. The control of accumulated waste in these systems
is considered critical to the success of the closed system, as is the effective cleaning
of the pond between cycles. This has resulted in very high water circulation using aerators
in the production ponds to keep the feeding areas clear of detritus and mud.
The solids budget above demonstrates that soil erosion is the most significant
source of solids input to the system, thus ( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture
164 1998 117–133 128 heavy water circulation results in high sediment accumulation and
increased suspended solids in the water. The heavy erosion of soil from the pond bottom
and its combination with detritus and faeces is potentially a method by which organic material
is removed from the pond system. By consolidating the highly organic detritus in a low organic
sediment the rate of diffusion out of the sediment could be slowed down. Many farmers
are all too aware of the problems with ammonia and disease they can cause if this
sediment is disturbed i.e., when aerators are moved . Many farms employing low water
exchange systems are still unable to maintain clean feeding areas due to inadequate
water circulation or poor aerator position. Deep ponds )1.5 m are difficult to
circulate using paddlewheels and airjet aerators have caused problems with erosion.
Removal of accumulated sediment during production is an option Hopkins et al., 1995
that is unknown in Thailand, although it shows great potential for lowering organic
loading in these systems. The problem with removal of the accumulated sediment is that
once it has accumulated it loses its fluid properties, becomes gel-like and cannot be
pumped out. A second problem is too frequent pumping would require addition of water
to the pond. click here to print

4.2. Lined ponds
One method by which many problems of earthen ponds especially low water
exchange systems can be avoided is the use of pond lining. Full pond liners bitumen
impregnated geotextile have great potential in separating the pond bottom from the
water column at the Tinsulanonda Songkhla Fisheries College. This eliminates soil
erosion and reduces the accumulation of sediment in the centre of the pond, resulting in
a larger clean feeding area for the shrimp and quick but efficient pond cleaning
typically 1–2 days with bulldozerrbackhoe for earth pond, 3 h with hose for lined
pond . Very little waste is left in the pond after harvest and the dryout time required for
earth ponds is not necessary. The characteristic of the small volume of accumulated
sediment found in lined ponds is completely different for that of earthen ponds.
Accumulated sediment in lined ponds is not consolidated 83% water vs. 62% water in
earth ponds , remains extremely liquid and can be easily pumped out of the pond. The
lack of soil in the accumulated sediment of lined ponds causes it to have a higher
w organic content 36% than in accumulated sediments of an earth pond ex-mangrove
x 13%. This high organic content is also reflected in the higher levels of leachable
nutrients in the accumulated waste of lined ponds. The higher levels of labile
Accumulated sediment analysis means"s.d. Funge-Smith, 1996
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 129
ammonia and dissolved reactive phosphorus in the lined pond waste have implications
for sediment management since these nutrients can act as fertilizers and, if in excess,
stimulate overblooming in the pond. On the other hand removal of these nutrients can
destabilize the phytoplankton bloom resulting in high water transparency. The former
situation is becoming usual at the Fishery College. The high organic content of
accumulated sediment from lined shrimp ponds can also be used as fertilizer after
desalting Bergheim et al., 1993
Despite the promise that lined and partially lined ponds can improve water quality,
production from these systems has not been fully convincing, possibly because new
management techniques are required. One reason for the observed cannibalism and
occasional high FCR in lined ponds, is the tendency for feeds to be rapidly carried to the
centre of the pond with water circulation. The contribution of the pond soil and detrital
feeding to shrimp nutrition and growth is uncertain in intensive ponds, lined ponds
might limit the availability of some nutrients to the shrimps. By forming a barrier
between the pond soil and the water, anaerobic conditions develop beneath the liner.
Adequate drainage must be provided to allow exit of seepage water. Gas formation
below the liner can cause it to float so weighting is also required typically concrete
strips or fencing posts . If pond soil is potential acid sulphate, the conditions below the
liner can become extremely toxic. In such situations, sand can be applied between the
soil and liner to facilitate drainage. Care must be taken to avoid seepage from adjacent
unlined ponds and canals.
The principal drawback of liners in shrimp culture ponds is their high cost and
relatively short service life. The lining material for ponds can cost between $1–3 m2 ,
and service life can be as short as 2 crops. More expensive liners last longer, but care
must be taken to avoid deterioration from exposure to sunlight if there is extended time
between crops. Ponds should be full of water even if there is no stock. Disposal of old
lining materials will become a problem if widescale adoption occurs, since burning them
appears to be the most likely method. click here to print

4.3. Recirculation and integration
Recirculating farms exist in Thailand but appear to have production problems
associated with salinity and disease transmission within the farm. In fully recycled
farms, water is recirculated through production ponds and into settlement, treatment and
storage reservoirs. If disease enters this system, it is very difficult to isolate and treat
parts of the system. The trend now is to use a limited water exchange system for the
production ponds, replacing water loss from treated reservoirs. This allows individual
ponds to be controlled if there is a disease problem. The large water area required for
these farms causes high salinity in the dry season, such that recirculated farms are filled
during periods of low salinity. Salinity can then increase through the dry season until
harvest. Second cropping is difficult since low salinity water is not available, but losses
from the system can be replaced with full strength seawater, and by the end of the
second crop lower salinity water is available. Systems such as this can only be used
when the farm is situated in estuaries or where river water is available.
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 130
Integration of other species such as fish, molluscs and seaweeds in the recirculating
system is not possible until the problem of heavy solids loading in effluent water can be
resolved. There are additional engineering problems when the farm cycle of four to five
months is not sufficient to produce a crop from the integrated species. Tilapia’s nest
building activity can disturb sediments, and the pseudofaeces from bivalves can cause
self-fouling and severe sediment problems in areas where they are cultured. Plankton
grazing fish species can be used to control phytoplankton. Mangrove oysters require a
diurnal tidal rhythm to grow effectively and cannot be flooded 24 h a day. Seaweeds
need cleaning every other day by shaking off the adhering sediments. Both bivalves and
seaweeds are extremely effective at removing solids from the water, bivalves by
filtration and seaweeds by trapping solids in the mucilage on the thallus surface. It
appears that the obstacles to successful integration lies in the solution of some
engineering problems and finding the potential markets for these low value species. It is
worth noting that if pond lining becomes widespread the lower inorganic solids loading
may enable successful integration of other species. click here to print

4.4. Low salinity
Recently, low salinity farms have increased in number dramatically due to the
establishment of closed system culture techniques. Clay ponds inland are filled to one
third of its capacity with sea water that is transported from the coast. The ponds are then
filled with fresh water and the resulting salinity is approximately 5–10‰. Alternatively
farms on inland estuaries that have access to very low salinity water can also now farm
shrimp. The problems of these farms are similar to the closed system ponds with respect
to sediment accumulation and heavy phytoplankton blooms although the higher salini-
ties favour dinoflagellates and low salinities tend to give rise to blue–green algae . Low
salinity ponds do not have a problem with increasing salinity, but if culture takes place
during a season when there is significant amount of rainfall, salinity will decrease in the
ponds and give rise to problems. If shrimp of appropriate age, then they can tolerate
salinities as low as 2‰ but this is not advisable for small animals. Seasalt placed in bags
in front of the aerators can slightly increase the salinity if necessary. Buffering in this
system is low due to low salinity and limes or bicarbonate can be used to boost this.
Generally growth rates are very fast in these systems and FCR can be as low as 1.3–1.4
Pornlerd Chanratchakool, Thai Department of Fisheries, personal comm. . However,
production cannot usually be extended beyond 90–100 days, so shrimp are still
y1 . harvested when they are still quite small 50 pieces kg . The occurrence of blue–green
algae may result to bad smell or poor taste of the shrimp but this rarely happens.
Middlemen often complain about these to be able to buy at lower price. click here to print

4.5. The future?
The range of shrimp farming systems and techniques currently available offer
solutions to many of the problems within the shrimp industry. These solutions can
improve the environment both within and outside the rearing pond environment. The
biggest threat facing the shrimp culture industry is its size and the density of farms in
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 131
shrimp culture areas. The high intensity production and high concentration of animals
offer the ideal environment for the evolution of new diseases especially viruses .
Although we may be better able to control the environment within a farm, there is
still constant threat of disease introduction from external sources. Viral disease transmission
via postlarval transfer is currently acknowledged to be a possible route of
introduction to farms and between shrimp producing countries. It is important therefore,
to control broodstock and postlarval transfer between countries. Research on captive
breeding of P. monodon will allow genetic improvement of stocks and also the
production of disease freerhigh health stocks. The reduction of pathogenicity of viral
diseases is likely to be more rapid than our ability to produce disease-resistant shrimp.
However, screening postlarvae and water to prevent entry of disease can be an effective
method in limiting transmission. The production of healthy postlarvae is of paramount
importance in many countries due to broodstock shortages and poor post-larval quality
and in itself is still a major economic and production constraint.
Within areas with established shrimp farms, it is important to ration the flow of
influent and effluent water NACA, 1994 . This is essential if disease is to be excluded
from farms and good environmental quality maintained. Rationing can take the form of
shared inlet and outlet canals, effluent settlement and storage and settlement of harvest
effluent. Waste removal from ponds, though largely innocuous although saline , can
seriously degrade water bodies if dumped on land.
Since most shrimp diseases have a strong environmental component in their expression
it is important that shrimp farmers are made aware of the effect of their actions on
the pond environment and on the environment surrounding their farms. This is of great
importance to the industry since regulation through policing is rarely effective due to
lack of resources and farmer resistance. The dissemination of reliable information to
shrimp farmers is vital since the principal source of information regarding culture
methods are the retailers of feed and chemicals. The vested interest of these commercial
organizations often results in inappropriate culture practices.
Aquaculture production methods that rely heavily on chemical intervention can be
viewed as stressful and therefore undesirable. Intensive systems utilizing high rates of
feed application are often undesirable due to the requirement for close control of the
pond environment. This is rarely achieved and thus the system is wasteful and often
susceptible to disease. The development of semi-intensive shrimp farms is often seen as
the most sustainable method of shrimp farming. However, the land requirement of this
system can result in the disruption of huge areas of coastal zone. In some countries, a
more limited, but more intensive form of shrimp culture might be appropriate. Unfortunately,
the investment in such systems is often prohibitive and the skills required to run
such farms are lacking.
Shrimp farming is now a feature of many tropical coastal environments and affects all
communities dwelling in the vicinity. Due to the dramatic effect of shrimp farming on
coastal economies, collapse of farms in an area can seriously disrupt local economies.
This is often due to the loss of existing livelihoods that cannot be replaced after shrimp
farms are developed. Whilst it is often desirable to generate income in coastal areas, this
has often been at the expense of the inhabitants of that area. The labour requirement of
shrimp farms and processing plants is only useful if the demand is sustained. To prevent
( ) S.J. Funge-Smith, M.R.P. BriggsrAquaculture 164 1998 117–133 132
the boom–bust effect of shrimp farming, all people involved should aim to maintain the
positive aspects of shrimp aquaculture whilst acting to ameliorate its negative impacts.
When considering coastal areas for development, it is vital that existing local
economies are evaluated correctly equitably and strong measures are taken to avoid
explosive expansion of shrimp farms. It has been demonstrated frequently that the ability
of a coastal area to support shrimp aquaculture is finite and that this ‘carrying capacity’
is often exceeded in the rush for quick profit. This approach, whilst commonplace, is
ultimately to the detriment of all parties involved. click here to print

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