In any earthen pond culture
system, the bottom soil play a
major role in pond yield. High
organic matter content in neutral
soil often promotes higher primary
productivity and hence higher fish yield. Natural food organisms are
one of the most important food
sources in ponds. It is rich in
protein, vitamins, minerals and
other essential growth elements
that simple supplementary feed can not complete. Fish yield in pond
can also be affected by the
presence of predators,
deteriorating water quality and
improper pond management.
Hence, pond preparation is a first step towards ensuring a better
pond production. Shrimp culture operation in Asia
can be grouped into three major
categories: a. Those that depend entirely on
natural food (extensive culture); b. Those that depend on both natural
food and supplementary feeds
(improved extensive and semi-
intensive culture; c. Those that depend entirely on
artificial diet (intensive culture). Irrespective of the culture
operation used, it is always
advisable to prepare the ponds in
sustaining high natural
productivity throughout the
culture period. 6.1 Soil sampling Prior to pond preparation, soil
samples are collected from the
pond bottom and the dikes for pH
and organic matter contents
analysis. Soil pH analysis is
generally conducted to determine lime requirement. This procedure
is important for newly developed
ponds where the occurence of acid
sulphate soils is common. When
acidic soil condition is detected,
corrective measures can be incorporated in the pond
preparation activities. Sampling of
soil is not necessary for well
conditioned ponds. Collection of samples must be done
on wet or moist soil using soil
augur or an improvised sampler
made of bamboo or PVC pipe.
About 12 subsamples in an S-
shaped pattern should be taken in a one hectare pond. Only the top
soil (0–15 cm) is sampled. Stones,
rubbish and coarse particles should
be removed before taking the soil
samples. The subsamples are
mixed thoroughly and a representative portion is taken and
labelled accordingly. This
representative portion is then air-
dried by spreading thinly on plastic
sheet and protected from direct
sunlight, wind and dust. The dried soil is then packed in labelled
plastic bag and send for analysis to
the nearest soil laboratory.
Request for result interpretation
may be included when submitting
samples for analysis. Fig. 12. Section of gate showing grooves for slabs and screen In most soil laboratories, it usually
takes one to two weeks before the
result can be given. Thus for
routine soil pH determination, the
shrimp farmer can take upon
himself to do the analysis using a pH meter. To prepare for the
analysis, the air-dried soil sample
must be pulverized using a
wooden mallet or mortar and
pestle. It is then passed through a
2-mm mesh sieve and stored in a properly labelled bag or glass jar.
The sample is ready for pH
determination (see Section 6.6.3). 6.2 Leaching When the pond soil is found to be
acidic, it is normally “leached.
This is done by flushing and
washing the pond bottom with
water to leach away undesirable
metallic compounds like aluminum, iron and excess sulfur ions. 6.3 Pond drying. The drying of the pond bottom is
the most practical cheap and
effective method of eliminating
undesirable species in pond prior
to the culture period. Drying
oxidizes harmful chemical substances especially sulfides and
facilitates mineralization of organic
matter. The pond is dried until the
soil cracks or when it is firm
enough to hold one's weight
without sinking more than 5 cm on walking over the surface. During the process of drying the
ponds, other activities must be
undertaken. These include repair of
dikes and gates, reconditioning of
pond bottom trench, levelling,
installation of screens and substrates. Substrate installation
such as twigs or coconut fronds at
the pond bottom are very
important in the first few weeks of
culture because the juveniles have
the habit of clinging on vertical surfaces. Aside from that,
substrates also serve other
purposes: (i) provide additional
surface area for some benthic food
organisms, (ii) provide shelter
against direct sunlight, and (iii) reduce mortality of shrimp
juveniles from predators. 6.4 Tilling Tilling or ploughing of bottom soil
improves soil quality by exposing
sub soil to the atmosphere there by
speeding up the oxidation process
and the release of nutrients that
are locked in the soil. 6.5 Control of Undersirable species which are
pests, competitors and predators
consist of finfishes, crustaceans,
molluscs, reptiles, amphibians,
birds and mammals. Pests are
species that generally do not have direct harmful effects on the
cultured stock. In most cases,
however, pests are also
competitors. Some pests for
example are certain species of
crabs that burrow into the dikes. These can destroy the dikes and
cause leakages which may allow
the entrance of undesirable species
or the escape of cultured stock
e specially in nursery ponds. Others
are wood borers and barnacles. Competitors are species that
compete for space, food, oxygen,
etc. with the cultured stock.
Generally, these are of different
species. Competition arises out of
the similarity in environmental demands which can pos e
limitations in the culturd species
development. Both intra specific
and inter specific competitions
prevail in any shrimp pond. It is
essential to minimize such competition by adequate
management procedures in
stocking of shrimp fry and
prevention of undesirable species
from entering the pond. Predatory species on the other
hand, are species that prey on the
culturd stock. These species include
snakes, birds, finfishes, amphibians,
crustaceans and mammals. The
presence of predators is a serious problem for shrimp growers
especially in nursery ponds.
Predators are generally, but not
always, larger than the culture
animals. In some predatory
finfishes for instance, there are a number of distinct structural
features such as the head is about
30% of the body length and the
horizontal width of the mouth
opening is about 40–50% of the
head length against 16–24% in non-predatory fishes. The
capability of the predators to
capture their preys is affected by
size, density, general behavior
(eg., escape instincts), color and
structure of the preys. 6.5.1 Important undesirable species in shrimp pond (a) Finfishes Predatory finfishes are especially
destructive to juveniles. The more
voracious ones are seabass (Lates calcarifer) and ten pounder (Elops hawaiiensis). Other common predatory species include tilapia,
thread fin bream (Polynemus sp.) and The rapon sp. which are very harmful to shrimp larvae. Finfishes that compete for food and
space with the cultured stock are
mullet (Mugil sp.) mud skipper (Periophthalmus sp.), clupeiods sp. and Leiognathus sp. (b) Crustaceans Crabs are one of the worst
predators and competitors in
ponds causing heavy damage to
the stock. Their dike boring
activities are the major causes of
water leakage in ponds. (c) Molluscs Some snails compete for natural
food in the pond. The occurence of
snails in shrimp ponds appears to
coincide with soft shelling in
shrimps. (d) Amphibians Frogs are considered the most
common amphibian predator. The
adult frogs are harmful when
present in sufficient numbers. (e) Reptiles Water snakes predate directly on
shrimp larvae and adults and are
therefore extremely harmful when
present in sufficient numbers. (f) Birds There are a number of wading
birds which cause serious problems
in shrimp farms such as the
kingfisher and grey heron. The
grey heron can swallow a whole
prey of 15–20 cm in size. These birds are especially harmful when
the shrimps concentrate in the
surface or other shallow are as
providing opportunity for these
aerial predators. (8) Mammals The lower mammals such as otter
often destroy their preys more
than predates. The animal usually
causes serious damages in a shrimp
farm by killing shrimps as they
enter the pond. 6.5.2 Methods in controlling undesirable species in shrimp pond. There are two usual methods used
in controlling undesirable species
in shrimp ponds - physical and
chemical methods. a. Physical method - The most
effective method in this category is
drying the ponds. Other methods
include installation of appropriate
screens in the oulet/inlet gates to
prevent entrance of undesirable species, proper maintenance of
dikes and water gates to prevent
leakage and to eradicate boring
organisms like crabs ans snakes
and setting up traps and bird-
scaring devices like strings of colored cloth streching across the
surface of the pond to scare
predatory birds. During the culture
period, selective harvesting or the
use of cast net can be resorted to
minimize the impact of undesirable species. b. Chemical method - Eradication of
undesirable species is very
effective, less cumbersome,
efficient and fast when using
chemicals. This is because chemicals
act as contact or systemic poison. There are several types of
chemicals used and collectively are
known as pesticides. The use of
organic pesticides such as Aquatin,
Brestan, Endrin, etc., is not
recommended in shrimp farming because these have residual effects
which destroy the fertility of the
ponds as well as being non-
selective or broad-spectrum
compounds in terms of biocidal
activity. In selecting pesticides, plant-extracted compounds are
recommended because these are
biodegradable and in most cases
contribute to the fertility of the
fertility of the pond soil. The
commonly used pesticides are: i. Rotenone - This chemical which is
extracted from grounded Derris sp. roots has been used as piscicide for
centuries in South America. It is a
selective poison affecting readily
the finfishes but not the shrimps at
certain concentrations. Commercial
rotenone is in powder form containing 4–5% rotenone. Effective dosage for commercial rotenone is 2 g/m3 for common predators and 8 g/m3 for eel. Crude rotenone can be extracted
from Derris plant by cutting the root into small pieces, crushed and
soaked overnight in water. The
crushed roots are squeezed to
obtain as much extract as possible.
The extract is then added to the
pond at the rate of 4 g of dry root/ m3 of water. Fresh derris root is more effective than the dry one. ii. Saponin - It is extracted from tea
seed cake which is a residue from
oil processing of Camellia sp. seed. It contains 10–15% saponin.
Saponin is widely used to eradicate
finfishes without toxic effect on
crustaceans especially shrimps. The
effectiveness of saponin decreases
with decreasing salinity. The recommended levels of application are 12 and 20 g/m3 for salinities above and below 15 ppt,
respectively. Saponin is used in
shrimp farms in Thailand, Malaysia,
Singapore and Taiwan even during
the rearing period because of its
piscicide activity. iii. Calcium carbide - It is applied into
the crab hole and enough water is
poured in the hole to activate the
calcium carbide which kills the
crab. iv. Tobacco dust - Nicotine is the
potent principle in tobacco dust
and is non-selective type of poison.
Since this is toxic even to shrimp, it
is generally applied during pond
preparation activities. The pond should be flushed well before
stocking. A dosage of 200 kg/ha is
used to kill undesirable species
especially snails which will take
about six months before the
population re-establishes. v. Ammonium sulphate - This
chemical compound which is also a
fertilizer (21-0-0) is effective in
eradicating undesirable species
when used in combination with
lime. The toxicant is ammonia which is released from the reaction
of ammonium sulphate with lime.
This chemical is applied together
with lime during pond preparation
at the un drainable portions of the
pond at a dosage of 1 part of ammonium sulphate to 5 parts of
lime. Lime must preferably be
applied first to raise the pH since
the rapid release of ammonia from
ammonium sulphate is dependent
on high pH (above 8.0). 6.6 Liming Liming is the application of calcium
and magnesium compounds to the
s oil for the purpose of reducing soil
acidity. It is usually applied during
or after the pond drying stage. 6.6.1 Action of liming The favorable actions of liming are:
(a) kills most micro organisms
especially parasites due to its
caustic reaction, (b) raised pH of
acidic water to neutral or slightly
alkaline value, (c) increases the alkaline reserve in water and mud
which prevents extreme changes in
pH, (d) neutralizes the harmful
action of certain substances like
sulfides and acids, (e) promote s
biological productivity since it enhances the breakdown of
organic substances by bacteria
creating a more favorable oxygen
and carbon reserves, (f)
precipitates suspended or soluble
organic materials, decreases biological oxygen demand (BOD),
increases light penetration,
enhances nitrification due to the
re quirement of calcium by
nitrifying organisms, and (g)
indirectly improves fine-textured bottom soil in the presence of
organic matter. Excessive liming, however, can be
damaging because it decreases
phosphorus availability through
precipitation of insoluble calcium
or magnesium phosphate. 6.6.2 Liming substances The chemicals used for liming of
soils are the oxides, hydroxides
and silicates of calcium or
magnesium since these are the
ones capable of reducing acidity.
Typical liming substances are the following: (a) Calcium oxide, CaO This is the only compound to which
the term lime may be correctly
applied. Calcium oxide is variously
known as unslated lime, burnt lime
and quicklime. It is manufactured
by roasting calcitic limestone in a furnace. Calcium oxide is caustic
and hygroscopic and is sold
commercially in powder and
granular forms. (b) Calcium hydroxide, Ca(OH)2 Calcium hydroxide is known as
flaked lime, hydrated lime or
builder's lime. It is prepared by
hydrating calcium oxide. It sold
commercially in powder or
granular forms. (c) Calcium, CaCo3 and mixed calcium-magnesium carbonate,
[CaMg (CO3)2] The carbonates occur widely in
nature. Among the common forms
that can be utilized as liming
substances are calcitic lime stone
which is a pure calcium carbonate
and dolomitic limestone which is a calcium-magnesium carbonate
with varying proportions of
calcium and magnesium.
Commercial calcium carbonate is
known as agricultural lime. The
carbonates are the least reactive of the three liming substances. 6.6.3 Determination of lime requirement There are several methods used for
the determination of lime
requirement in ponds. One of these
is the Boyd's method which is
relatively easy to perform. The
procedure is as follows: Weight 20 g of the seived soil
sample in 100 ml glass beaker and
add 20 ml of distilled water. Stir
intermittently for one hour. Measure the pH of the above
solution with a pH meter
previously standardized and
record the reading. Add 20 ml of p-nitrophenol buffer
to the above solution and stir
intermittently for 20 minutes. Prior
to reading its pH, set the pH meter
to pH 8.0 with 1:1 mixture of the p-
nitrophenol buffer and distilled water. Read the pH of the soil sample
(buffer/distilled water mixture)
while stirring vigorously. Use the values of the soil sample
pH in distilled water and soil
sample in buffered solution to
obtain the liming rate from Table
1. If the pH of the soil in the buffered
solution is below 7, repeat the
analysis with 10 g of soil sample
and double the liming rate from
Table 1. Table 1. Lime requirement in kg/ha of calcium carbonate (neutralizing value of 100) to increase total hardness and total alkalinity of pond water above 20 mg/L Mud pH in water Mud pH in brffered solution 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 (kg/ha of calcium carbonate required) 5.7 121 242 363 484 605 726 847 968 1 089 1 210 5.6 168 336 504 672 840 1 008 1 176 1 344 1 512 1 680 5.5 269 538 806 1 075 1 344 1 613 1 881 2 150 2 419 2 688 5.4 386 773 1 159 1 546 1 932 2 318 2 705 3 091 3 478 3 864 5.3 454 907 1 361 1 814 2 268 2 722 3 175 3 629 4 082 4 536 5.2 521 1 042 1 562 2 083 2 064 3 125 3 646 4 166 4 687 5 208 5.1 588 1 176 1 764 2 353 2 940 3 528 4 116 4 704 5 292 5 880 5.0 672 1 344 2 016 2 688 3 360 4 032 4 704 5 376 6 048 6 720 4.9 874 1 747 2 621 3 494 4 368 5 242 6 115 6 989 7 974 8 736 4.8 896 1 792 2 688 3 584 4 480 5 376 6 272 7 186 8 064 8 960 4.7 941 1 882 2 822 3 763 4 704 5 645 6 586 7 526 8 467 9 408 Source: Boyd 1979 To prepare a p-nitrophenol buffer
of pH 8.0. Dilute 20 g para-
nitrophenol, 15 g boric acid, 7g
potassium hydroxide in one liter of
distilled water. Make sure that the
chemicals used are all reagent grade. Check the pH using a
standardized pH meter and adjust
to the right pH by adding 7.5%
potassium hydroxide (7.5 g/100 ml
distilled water) or 1.5% boric acid
(1.5 g/100 ml distilled water). Use medicine droppers to dispense the
solutions. Refrigerate the buffer
while not in use. It will last
indefinitely. Care must be exercised
in the use of p-nitrophenol as it is
toxic and reportedly carcinogenic. Potassium hydroxide is very
caustic and should be handled with
care. As a rule, never handle the
chemicals with bare hands and
flush with plenty of water should
contact occur. Generally, the liming material used
in ponds is calcium oxide. It is
therefore necessary to convert the
liming rate to calcium oxide value
by multiplying the above rate with
0.56. 6.6.4 Methods of liming Liming can be done in three
different ways: by broadcast over dried pond
which includes the dike walls. by mixing with water and spraying
over the pond, and by liming the water flowing into
the pond. In general, any one of these
methods may be employed.
Certain cases, however, demand
the application of a particular
method. In using the first two
methods, lime should be spread as uniformly as possible over the
complete surface of the pond or
pond water. Liming the pond water
is usually carried out with the use
of flat boat. The third method is
uncommonly practicec although it saves the labor in spreading. 6.7 Fertilization One usual way of increasing
carrying capacity of a shrimp pond
is to improve its natural fertility
through the addition of organic or
inorganic fertilizers. Pond
fertilization is an important and necessary step in extensive and
semi-intensive methods of farming
operations. (a) Organic fertilizers The most common fertilizers are
animal manures, rice bran,
compost and sewage. Application
of organic fertilizers especially in
newly developed ponds is
advisable because it serves as soil conditioner. The advantages and
disadvantages of organic fertilizers
are listed in Table 2. The rate of
application for shrimp ponds
ranges from 500 to 2,000 kg/ha. (b) Inorganic fertilizers Inorganic fertilizers are synthetic
fertilizers that generally contain
concentrated amount of at least
one of the major plant nutrients
like nitrogen, phosphorus and
potassium. These major nutrients are expressed on a percentage by
weight basis. Nitrogen is expressed
at %N and phosphorus as %
Phosphorus oxide (P2O5). Commercially available inorganic
fertilizers are usually sold with
such trade names as 16–20-0
(16%N-20%P2O5 -0%K2 O), 14-14-14 (14%N-14% P2O5 -14%K2O), 45-0-0 (urea). The rate of application ranges from 25 to
100 kg/ha during pond
preparation.
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