Liberal use was made of materials found from Cook and Rabanal (Eds.) “Manual on Pond Culture of Penaeid Shrimp”, ASEAN, 1978.
Pond preparation coincides with the tidal behaviour and season at the farm site. A period of 30 days is normally needed for the preparation of the pond.
Drain the pond completely during low water neap tides, after harvest. Allow the pond bottom to dry until the top layer of soil, 1 cm depth, is dry and/or the soil cracks 1 to 2 cm deep. Remove accumulated mud and organic debris from the internal peripheral canals. The excavated sediment is usually thrown on the dike by hand. It is important to make sure that the removed material is not washed back into the pond again with the first heavy rain.
While the pond is drying, repair of the dikes, gates and screens is done. Acidity in ponds with a soil pH lower than 6.5 is controlled by repeatedly filling and drying. A change of water is required at least every three days. Lime can be used to control further soil and water acidity. The recommended application rates are given in the following text table to bring the pH of the pond water to 7.
Type of soil and corresponding amount of lime needed per ha
| Soil (pH) | Clay loam (kg)2 | Loam sand (kg)2 | Sand (kg)2 |
| below 4 | 4 000 | 2 000 | 1 250 |
| 4.0 – 4.5 | 3 000 | 1 500 | 1 250 |
| 4.5 – 5.0 | 2 500 | 1 250 | 1 250 |
| 5.0 – 5.5 | 1 500 | 1 000 | 1 000 |
| 5.5 – 6.0 | 1 000 | 500 | 250 |
| 6.0 – 6.5 | 500 | 500 | 0 |
The pond bottom at the platform area is levelled when necessary. Tilling is done only when the bottom is hard and production during the previous culture period was low.
After the ponds are drained and dried, the eggs and larvae of competitors, predators, and pests that may have been left in peripheral canals could be killed by poisons. Details of operation is given in Section 4.6. The water should be drained after the application of the pesticide. A second treatment may be necessary to remove some undesired animals that may survive after the first treatment.
Fertilization to increase the fertility of soil could be done during the preparation of the pond. The fertilizer used could be either organic or inorganic or a combination of both. The details for the application of fertilizer is given in Section 4.3.
On the 22nd day, water is taken in and gradually raised to 120–130 cm. The minimum depth of water at the peripheral canal should not be less than 50 cm to ensure that the temperature does not go up beyond the tolerance limit for the shrimp.
Stocking is done during the coolest part of the day. It has been found that before 0900 hours or after 1800 hours are the best times.
It was believed that shrimp postlarvae (PL) that are ready for the nursery pond should be at least PL25. New evidence, however, obtained from the field tests at Jepara Brackishwater Development Center, Jepara, Indonesia, suggested that shrimp postlarvae even at PL5 are strong enough to grow in the nursery pond system.
The larvae holding capacity of the nursery ponds depends principally on the pond environmental conditions. Pond depth between 50–100 cm with a good growth of natural food is capable of holding between 50–100 pieces of fry per m2 for good growth and low mortality. This gives a stocking rate of from 40 000 to 80 000 postlarvae for the 800 m2 nursery pond. Initially, stocking rate in nursery pond will be 10 postlarvae per m2 or 8 000 postlarvae1.
The fry are acclimatized to the pond water temperature by allowing the fry plastic bag to float in the pond water for about 15 minutes. The bag is then opened and water is gradually let in. The fry are then released after salinity and temperature inside the bag approximate that of pond water conditions.
Shrimp at larval stages prefer to cling to suspended material rather than burrow in the mud. The survival rate of shrimp in a nursery pond is better if sheltering is provided. This is done using twigs of trees or coconut leaves spaced at least 1 m apart along the peripheral canal (Fig. 12). These shelters besides providing refuge for shrimp fry against predation and cannibalism during molting also serve as additional substrate for algal growth.
After stocking, the water of the nursery pond is increased and maintained to about 50–100 cm. Every three days, freshening is done by letting out the lower layer of the pond water during low tide and admitting in new water during high tide. This stimulates the growth of the shrimp fry and improves water quality. During the process, the gate is carefully screened to prevent the escape of the fry and the entrance of predators.
Filamentous green algae or “lumut” should not be allowed to grow inside the nursery pond because the fry might get entangled with the algal filaments and eventually die if they cannot free themselves. The dense and thick colony of “lumut” also prevents the free movement of the fry especially when they have to stay in the bottom to avoid the excessive heat of the sun.
Shrimp fry grow fast in the nursery pond. At a stocking rate of 75 pieces per m2, the fry from PL5 with an initial size of about 6.3 mm in total length and 0.01 g in weight will attain an average size of about 66.30 mm in total length and about 1.82 g in six weeks. The growth rate of the shrimp fry in the nursery pond during the two-month period is 7.50 mm per week in total length and 0.55 g per week in weight. The text table below show the growth rate of P. monodon in an earthen nursery pond.
| Rearing period (days) | Total length (mm) | Weight (g) |
| Initial size | 6.3 | 0.01 |
| 15 | 19.0 | 0.08 |
| 30 | 34.0 | 0.25 |
| 45 | 58.0 | 1.75 |
| 60 | 81.3 | 4.60 |
Transfer is done by making the fry move with water flow. A cut is made at the tertiary dike. The following methods are suggested:
Transfer at the time of the month when tidal amplitude is greatest.
Transfer at night and use a light to attract the shrimp to the dike opening.
Let a little amount of water into the nursery pond during high tide preceding the transfer. Water surface elevation in the rearing pond should not be more than the elevation of the bottom of the sheltering canals of the nursery ponds. Transfer is then done on the next low tide.
Change pond conditions to make the shrimp become active and ready to move out of the pond. One way of doing this would be to lower the water level so the temperature of the pond is increased.
For shrimp culture, benefits of fertilization are indirect. Fertilization is a provision of some vital elements required by plants for primary production which may be used up by the organisms after a certain period. The nutrients will stimulate the growth of the phytoplankton, and causes its bloom for micro-organisms. The micro-fauna feed on the phytoplankton which in turn is fed on by shrimp. There are two kinds of fertilizers being used in shrimp culture practice at present, organic fertilizer and inorganic fertilizer.
The organic fertilizer could increase natural foods in shrimp pond through the two elements of the basic food chain. The mineralized fraction of the manure provides nutrients for enhancing the growth of phytoplankton which, in turn, produces oxygen through photosynthesis, while the non-mineralized fraction of the manure is used directly as food for zooplankton.
There are many kinds of organic fertilizers with different nutrient composition (Table 3) that could be used in shrimp ponds. Among these are pig dung, chicken manure, cow dung, sheep dung, horse dung, rice bran, sugar cane molasses, peanut cake, coconut cake, etc.
For basic fertilization given during the preparation of pond, chicken manure and pig dung could be applied at the rate of 500–750 kg/ha while cow dung or horse dung could be used within the range of 1 000–2 000 kg/ha.
During the rearing phase, additional fertilizer might be required from time to time to stimulate the growth of natural food which may subsequently vanish due to consumption by the cultured animals. The heavy application of organic fertilizer in pond in this period could result in the hazard of shrimp kill due to depletion of dissolved oxygen in the pond water brought about by decay of the added organic matter. The oxygen depletion resulting from addition of manure could be quantitatively predicted from measurements of the biological oxygen demand (BOD) of the manure at pond temperature. The BOD in turn could be estimated from the amount of dry organic matter in the manure. With the ability to predict oxygen depletion, it was feasible to add organic fertilizer weekly with the minimum hazard to the cultured shrimp in the pond.
Inorganic fertilizer contains three major plant nutrients, N, P, K. Nitrogen is the most essential element. The assimilation of nitrogen by the shrimp is a link in a cycle of chemical transformation in which bacteria play an important role. Normally this element could be perpetually supplied through the surface of the pond on contact with the atmosphere. Therefore, the usefulness of an addition of nitrogen from fertilizer depends on the degree of nitrogen fixation by both bacteria and algae. To provide a suitable amount of nitrogen to a shrimp pond system as required by bacteria and algae is rather dynamic.
Phosphorus is the most important element. It is a limiting factor in growth of phytoplankton. Absorption of phosphate (PO4) from water is proportional to the concentration of the anion in the water. It should not give too high until it becomes toxic to the shrimp.
Potassium is also an essential element for plant growth. It is effective in stimulating the growth of aquatic flora. In shrimp ponds potassium required is small, and its availability is usually in excess to the amount required by the organisms. This is the reason that a complete fertilizer like 14-14-14 is not utilized in shrimp ponds.
Some fertilizers may contain more than one primary nutrient. In this category, the elements are designated by a numbering system indicating percentages of each element. The number system is always listed in the following order, N, P, and K. For example, an 18-46-0 grade fertilizer contains 18% of nitrogen, 46% phosphorus and 0% potassium.
Inorganic fertilizer commonly used in shrimp culture practices are urea-CO(NH2)2, and triple-superphosphate (TSP) - P2O5. The former contains N about 46.6% while the latter contains 39% of P. The main considerations in the application of inorganic fertilizer is to supplement the primary nutrients (N, P) as essential for the growth of micro-organisms in ponds. It should be kept in mind that both urea and TSP do not remain in solution for a long period. They become incorporated in the bottom soil by precipitation or absorption. If great amount of fertilizers is applied, the excess portion will precipitate on the pond bottom and become decomposed subsequently by bacteria. This process does not only foul the pond bottom but the low oxygen content and high quantity of dissolved organic matter on the pond bottom also induce diseases like black gill disease, black or brown shell disease to the shrimp in subsequent period. The poor quality of pond water also forces the shrimp to co-exist with overburdening organisms resulting in slow growth of the shrimp.
For the application of inorganic fertilizer in shrimp pond, it is more advantageous to use this during the preparation of the pond only. If one wishes to use it during the rearing phase, a moderate amount of the fertilizer should be applied. For basic information a level of 0.95 ppm N and 0.11 ppm P should be suitable as a starting dose. The amount of the fertilizer can be reduced or increased depending on the growth of the phytoplankton in subsequent period. For unskilled shrimp farmers the density of the phytoplankton can be measured by a secchi disc. A secchi disk disappears from sight at less than 25 cm the phytoplankton is too dense and the pond water should be changed. The next application should be reduced. If the secchi disc disappears from sight at more than 35 cm, the phytoplankton growth is not enough and more fertilizer should be added.
Numerical example: A one-hectare shrimp pond has a surface area of 10 000 m2. If the average water depth of the pond is about 0.60 m, the volume of water in the pond would be 10 000 x 0.60 = 6 000 m3. One ppm is equal to 1 g to 1 m3 water. Hence, the amount of N should be added to the pond to get a level of 0.95 ppm N is 6 000 x 0.95 = 5 700 g or 5.7 kg N. If the pond is fertilized with urea containing 46.6 percent the amount of urea required is 5.7/0.446 = 12.23 kg.
For TSP which contains 39 percent P, the amount required can be calculated in the same manner.
Frequent water change has a beneficial effect on water quality in a pond. It also introduces new food organisms to a pond. During spring tides, the lower layer of the pond should be drained out as new sea water is admitted in the incoming high tide. Two schedules for changing water are presented below:
Water is changed every 12–14 days. When changing water, one-thrid of the water in the pond is drained and replenished each day for two or three days. Fertilizer is applied after the water change and then again after six to seven days.
One-half to one-third of the pond water is exchanged once a week. Fertilizer is applied after every change of water.
If the shrimp is under stress, pumping is resorted to without waiting for the high tide. Fresh sea water is admitted into the pond as drainage of the old water is done simultaneously. During heavy rain, the top layer of water should be allowed to overflow the flashboards so that the salinity of the pond water does not decrease below 10 ppt. During the dry season, freshwater will be needed to control the salinity of pond water to below 25 ppt.
During the rearing phase, daily maintenance of the pond is required. Dikes are repaired as required by filling the crab holes and preventing water from seeping through. Extermination of the undesired fish by applying derris root or teaseed cake may be required from time to time. Cleaning nylon screens at the sluice gate is done to maintain better water flow.
Shrimp is predominantly carnivorous. It seizes food with its pincers and then pushes it into its mouth. In ponds, it may be seen nibbling on “lab-lab” from time to time. Chironomid larvae, Tendipes longilobus and mysid, Mesiodopsis are other components of good natural food for penaeid shrimps in ponds. The growth of these animals are promoted by the application of fertilizers.
Lab-lab - it is characterized mostly by benthic blue-green algae and diatoms and other forms of plants and animals associated with it. Growth of lab-lab is directly related to the amount of organic matter present in the soil. The recommended dose for the first application is 350 kg/ha TSP and 500 kg/ha of rice bran. Immediately after applying fertilizer, 5 cm depth of water is let into the pond. The best growth of lab-lab is found at salinity of from 25–30 ppt. After one week, the same amount of fertilizer is applied and the water level is raised to 10–15 cm. The fertilization is repeated after the second week, and the water is raised to 20–25 cm. Good lab-lab growth should be observed after the second week.
Phytoplankton - it has been observed that the growth of shrimp is better in ponds in which the most common type of algae are diatoms. Poor growth has been observed where the predominant algae are flagellates. N to P ratio of 20–30 has been found most suitable for diatom growth. Shrimp do not feed directly on the phytoplankton. They feed on the zooplankton that eat the phytoplankton or on the bacteria that grow on the dead phytoplankton cells which accumulate on the bottom.
Phytoplankton production is better in ponds with water of 70 cm or more. Most phytoplanktons are normally found in relatively deeper water where temperature does not rise as high as it does in shallow ponds.
Benthic animals - heavy application of organic fertilizers encourages the growth of chironomid larvae which provide good growth of shrimp. Dense populations of chironomids are often associated with low levels of dissolved oxygen. Care should, however, be taken in encouraging dense growth as chironomids graze heavily on lab-lab.
“Lumut” - soft mud bottoms with pH of 6.8 to 7.5 favour the rapid growth of lumut (filamentous green algae). The pond bottom is dried for lumut culture only for three days. After the bottom has been dried, sufficient water is left in to moisten the soil and then the pond bottom is seeded. This is done by sticking a portion of the filaments of very young plants, or light green ends of older plants, into the mud. It usually takes two to four weeks from the time of planting until the pond is ready for stocking. After the seeding is completed, the pond is flooded to a depth of 20 cm. Three to seven days after planting, the pond is fertilized with a 16-20-0 inorganic fertilizer at a rate of 18–20 grams per cubic meter of water. The fertilizer can be applied by broadcasting or by dissolving from a platform (Fig. 36) placed 10 cm below the water level. After one week, the water level is raised to 40 cm. Starting with the second week, weekly application of fertilizer at the rate of 9–10 grams per cubic meter of water is continued until six weeks before the crop is harvested.
In unfertilized or underfertilized ponds, the starting growth of lumut is yellowish-green. As growth continuous, the colour turns to grass-green. When the plants have reached the surface and spread out, only the fringes and those directly over the bottom continue to have this healthy colour. Those on the top, especially the centre of the floating mess, becomes yellowish. During the dry season, this colour changes to dirty-brown.
In contrast, algae in correctly fertilized ponds retain a healthy grass-green colour. Clear indications that the amount of fertilizer is too little are slow growth and yellowing of the algae. A slight overdose of fertilizer causes the algae to become dark-green.
Rows of twigs and small branches should be placed in the pond to keep the wind waves from dislodging the lumut.
Supplementary feeding is done to supplement natural food productivity or as an emergency measure when growths of natural food in a pond becomes depleted. There are a wide range of supplementary feeds for shrimp that the farmer can select from. These are trash fish; rice bran with trash fish, crabs, molluscs, and shrimps; carabao skin and other slaughter and poultry houses leftovers (cut the carabao skin into 30 cm square pieces, these are attached to sticks and scattered through the pond); prepared hog and poultry feeds; mussel and clam meat; chicken feed (crumbs and pelts); and processed foods.
Extermination of predators, competitors and pests in shrimp ponds is necessary for proper shrimp farming management. The following have been identified as causing problems in shrimp culture.
| Predators | Competitors | Pests |
| Fish | Snails | Crabs |
| Crabs | Fish | Burrowing shrimps (Thalassina) |
| Birds | Crabs | Organisms which degrade wood |
| Man | Shrimps | Mud worm egg cases |
| Insects | ||
| Snakes | ||
| Lizards |
The most effective method is prevention. Proper pond preparation and maintenance should be taken. Predators and competitors can enter ponds through crab holes and other leaks in the dikes. Crabs should be eliminated and their holes plugged. Closure boards in the sluice gates should fit tightly.
Thoroughly drying the pond bottom before stocking will eliminate the fish. If the pond cannot be thoroughly dried, derris root is recommended at 4–5 kg/m3 of pond water with depth of 5 cm.
After fish are eliminated from a pond, it is important that all water let into the pond is screened. The screen must be fine enough to prevent entry of fish eggs and larvae as well as adult fish. A fine mesh nylon with hole size of 0.5 mm is recommended. It is often necessary to have a series of screens of different mesh size and to increase the surface area of the finest screen by making it into a bag. If the end of the bag is connected to a floating screened box, trash and fry will collect and these can be removed with a dip net. The shrimp fry can then be separated and stocked in the pond. In ponds which are filled by pumping, the nets should be placed before the pump.
When the number of fish in a pond is large, the most effective method to get rid of them is by the use of selective poisons. The use of natural products such as teaseed cake or derris root is recommended. Use of any of the chlorinated hydrocarbon group (DDT, Endrin, Chlordan, Gamma BHC, etc.) in shrimp ponds is not recommended because of their long-term residual effects.
In order to apply the correct dose of a chemical, the amount of water in a pond must be estimated. First, the total water surface area of the pond must be known. This is then multiplied by the average pond depth to obtain the number of cubic meters of water in the pond. Listed below are possible piscicides:
Teaseed cake - this is a residue from the processing of oil from the seeds of Camellia. The cake contains 10–15 percent saponin. The recommended level of application is:
Salinity above 15 ppt = 12 g teaseed cake per cubic meter of water
Salinity below 15 ppt = 20 g teaseed cake per cubic meter of water
To apply teaseed cake, it must be ground up. Heating in an oven dries out the cake and makes it more brittle and easier to grind. Ground cake is soaked in water for 24 hours to extract the saponin. The water containing the saponin can be filtered and the filtered fluid is applied to the pond water. When using teaseed cake, or any other chemical, the level of water in the pond should be lowered as much as possible without causing damage to the shrimp by the resulting increase in pond water temperature. It is best if the pond water level is lowered in the late afternoon or evening, and the chemical then applied. Water level in the pond could be raised the next morning before the sun heats up shallow pond water. Dead fish should be removed from the pond.
Rotenone - this has been used to selectively kill fish but not shrimp. However, the difference between the lethal limit for fish and shrimp is small. The volume of water in the pond must be estimated accurately as an overdose will kill the shrimp. Rotenone works well in low salinity water than in high salinity.
Rotenone powder available in the market usually contains 5 percent rotenone. The recommended level of treatment is 0.2 ppm rotenone. This requires 4 g of 5 percent rotenone powder per cubic meter of water.
Derris root - this is one of fish toxicants that is widely used in fishponds. It is commonly called tuba in Indonesia, Malaysia and the Philippines. The term is used generally by the natives for several poisonous plants which are chiefly used for catching fish. Among those found in Malaysia are Derris elliptica, D. malaccensis. The active component of derris is rotenone. The rotenone content in derris root varies depending on the age and the freshness of the root. Fresh roots are more effective than dried roots which have been stored. The rotenone content is also higher in small roots than in large roots. The roots should be cut into small pieces and soaked overnight in water. After the soaking, the roots are pounded to crush them. The crushed roots are then placed back into the water in which they were soaked and squeezed so as much of the rotenone as possible goes into solution. Four grams of fresh roots are required per cubic meter of pond water.
PCP-Na (Sodium pentachlorophenate) - This is an agricultural chemical used widely as a weed killer. It kills fish at treatment levels which do not kill shrimp. The recommended level of treatment is 0.5 ppm. The correct amount of the chemical is dissolved in the freshwater and the solute is then spread evenly around the pond. Rubber gloves should be worn or a stick should be used to mix the chemical with freshwater. Fish killed with PCP-Na should not be eaten.
Mud crab, Scylla serrata, Uca annulipes, U. marionis and U. dussumieri are commonly found in shrimp ponds. Mud crab is a fierce predator of shrimps while the others compete in food and space. The animals also damage the dike and cause water leakage through their holes. These should be removed from the pond by trapping. Fish with firm meat such as catfish or shark are recommended as bait.
Small balls of “Sevin” (a pesticide) mixed with ground fish are placed in crab holes above the water line. Calcium carbide is also put into crab holes and enough water is poured into the hole to wet the carbide. The acetylene gas produced kills the crab. Tobacco dust and other pesticides like “Brestan” and “Aquatin” can kill on direct contact. Rice hulls are burned and the residue is used to fill up the crab holes. The hulls stop the functioning of gills of the crabs so that they die subsequently.
Thalassina also damage the dike. Their burrows along the dike are one of the causes of water leakage. Their holes can usually be distinguished from those of other crabs for their very high mounds at the hole entrance above the water line. The same method to eradicate the crabs can be used for Thalassina. Bamboo type trigger traps can also be used.
Snails compete for the natural food in the pond. They disturb the pond bottom algae and as a result during windy days the pond can become muddy and/or the lab-lab breaks loose from the bottom and floats to the surface. Wind action carries this to the pond bank where it settles and decomposes and produces large amount of hydrogen sulphide.
The most effective method of control is to dry the pond bottom and to apply poisons before stocking to kill the larvae and eggs of the snails. Chemicals like Brestan, Aquatin, and “Bayluscide” can kill the snail when used at the dosage prescribed on the package, but their residual harmful effect after application limit their uses in shrimp ponds. It was observed that shrimp ponds in Indonesia have a significant low production of shrimp for at least 12 months after the application of Brestan. Aquatin also retards the growth of lumut and its residual effect in pond soil extend for five years. Bayluscide and Aquatin stunt the milkfish when used in fishponds.
Predation by wading birds can be of a problem. Most wading areas at the sides of the ponds where birds will land can be reduced or eliminated by making the sides of the dikes slope steeply to the deep peripheral canal. The dike berms should be placed above the water line and mangrove or other branches placed on it to prevent birds from walking along the shallow pond margin.
In nursery ponds, some farmers run lines of string between posts set in the pond and attach bright coloured pieces of cloth metal to the spring to scare birds. Flashing mirrors can be used to scare some types of birds away from fishponds.
Losses caused by man are perhaps the hardest to prevent and for this reason, a watchman should be hired especially during the last third of the growing period. Tree stumps left untouched at the shallow pond platform make it difficult for poachers to catch shrimps with cast or seine nets.
Where wood is used especially for secondary and tertiary gates, destruction of wood by marine organisms can be reduced greatly by using special kind of wood or by coating the wood with preservatives.
Shipworms (Teredinidae, Pholadidae) and the crustacean, Isopoda cause damage by boring. Fungi cause wood rot.
Preservatives such as creosote is the most effective treatment for increased wood resistance to the various organisms. Brush or surface treatment is usually practised but if possible should be applied under pressure. Otherwise, if pressure treated wood is not available, the wood should be soaked in the preservative. An external coating of tar or asphalt is usually done and excellent results have been reported by first applying the asphalt or coal tar and then applying cement on the still soft coating.
Flashboards or slabs are given frequent applications of the preservative and can also be soaked in chemicals to kill the pest. If two sets of boards are made, one can simply be left to air dry and the borers will be killed.
The indicators of trouble and possible remedial action are enumerated and described below.
The presence of dead shrimp or fish.
A die-off of algal growth. This can sometimes cause milky coloured water.
An overgrowth (bloom) of phytoplankton can cause oxygen depletion. This can be especially harmful on cloudy days that follow several days of bright sunlight. Caution should be exercised if one cannot see a white coloured object 25 cm deep in the pond. Check in the early morning to see if shrimp or fish are swimming erratically at the surface, frequently breaking the water surface.
Active swimming of shrimp at the water surface during daylight hours. This indicates the shrimps are in stress. The usual cause is low oxygen and/or high temperature.
Active swimming of shrimp around the edge of the pond during daylight hours, but not at the water surface. This can indicate a lack of food in the pond.
An abrupt change in water colour. If the water becomes clear, it means the phytoplankton died and a shortage of natural food has developed. If the water turns reddish or bright green, green colour, types of algae might be present which give off toxins which can kill the shrimp.
Bad smell. A smell of sulfide or rotten eggs is caused by hydrogen sulfide. This is produced by decomposition and it can indicate that an accumulation of organic matter has occurred on the pond bottom. The most frequent cause of this is lab-lab which floated to the surface and was carried to a corner by the wind. During night hours it sinks to the bottom where it decomposes. If the smell comes up from the bottom mud while someone is wading in the pond, the bottom is bad.
Gobies swimming in stress and/or concentrated on the sides of the dikes can indicate low dissolved oxygen in the pond water.
Snails climbing out of the water can also be an indication of low oxygen in the water.
A heavy concentration of the rotifer Brachionus or other form of zooplankton in the pond water can indicate either a build up of organic matter in the ponds as a result of decomposition of other food organisms or a heavy growth of bacteria.
Shrimp with black gills. This condition can be caused by disease or by the shrimp burying in the mud made black by decomposition. Place the shrimp in clean water and if the black colour goes away after one or two days, it is accumulated debris; if the colour remains, it is a disease.
Shrimp with white discolouration on their tails. This can be caused by disease or by the stress of low dissolved oxygen and high temperature. In the last case, the shrimp are usually swimming actively and show signs of stress, some may even be jumping out of the water. Some of these shrimps will lose the white spot if placed in well-aerated water for a day.
Shrimps with papery shells and body that pushes in easily. This is usually caused by lack of food.
Abrupt lowering of salinity in a pond, especially when caused by heavy rains. The freshwater floats on top of the salt water. This forms a barrier and the bottom water often can become deficient in oxygen.
Temperature above 32°C. A higher temperature of pond water is dangerous and can lead to increased mortality.
Low pH. In brackishwater, a pH of 8 to 8.2 is normal. A pH lower than 7 is a cause for concern in that it indicates some abnormal condition in a pond. A high pH is usually associated with a good growth of phytoplankton. It is not a cause for concern unless it rises above 9.5.
Low levels of dissolved oxygen in pond water by measurement usually during early morning hours before sunrise.
Bottom mud containing a large number of chironomid worms and nothing else. Chironomid worms are an indicator of pollution. They can live when dissolved oxygen levels are very low, and when everything else dies their numbers increase. They are very small red worms.
Numerous shrimp with black spots that look like an old injury. This is caused by a bacterial disease, and is usually associated with water with a high organic content. In any case, they are an indication that growth is slow and the shrimp are not molting.
A foam is formed on pond surface by waves during high winds. This happens to water with a high amount of dissolved organic matter.
1 See Cook and Rabanal, eds., 1978
Water exchange - changing water is a general preventive and/ or remedy for most of the conditions listed above: It introduces new oxygen, dilutes waste products or phytoplankton that may have built up too high, introduces new food organisms, trace minerals and organics, dilutes disease causing organisms. It is important that water be exchanged as soon as possible in cases where low dissolved oxygen is the problem. Oxygen depletion usually occurs near the bottom and it is best to drain and replenish water from the bottom most of the time. A pump should be made available to flow water into the pond. In the case of low salinity of the surface layer caused by heavy rains, water should be drained from the top and replenished from the bottom.
Mechanical mixing - water can be mixed to supply oxygen or to break up a layer of freshwater. Mechanical agitators or, in an emergency an outboard engine can be used.
Addition of chemicals - addition of chemicals like potassium permanganate could be useful remedy for low dissolved oxygen levels. Hydrated or quick lime applied at rates from 200 kg/ha has been used. Quick lime is a special type of activated lime and should not be confused with agricultural lime. It is caustic to handle and bulky.
Raise water level - in ponds with high temperature, the water level should be raised. In some cases, it may be necessary to provide shade. Rafts or bamboo supporting banana leaves would be inexpensive.
Stop feeding or fertilization - any time shrimp appears to be in stress, or pond conditions are poor, supplemental feeding or fertilization should be postponed until the situation is corrected.
Remove dead fish or algae - this should be standard procedure. Anytime dead things are observed in the pond, they should be removed.
Add feed - if the shrimp gives signs of being undernourished or hungry, it might be useful to supply extra food until a new growth of natural food can be produced.
Transfer shrimp - in some cases where shrimp in a pond have stopped growing, growth resumed when they were transferred to another pond with a good crop of natural food.
Harvest shrimp - total harvesting is advised only as a last resort when a large percentage of shrimp in a pond are diseased or are dying from bad pond conditions and there is no way to remedy the situation. Partial harvesting can be utilized when there is evidence of slow growth caused by lack of food. Selective harvesting can be used to reduce the number of shrimp in the pond by cropping large individuals and leaving the smaller ones to grow larger.
The most common disease is the blackening of the gills and black gills in shrimp are caused by:
Accumulation of debris in gills - this is associated with poor pond bottom conditions. The shrimp with dirty gills are placed in clean water.
Fungus - in shrimp infected with fungus, Fusarium sp. the gills have a very dark, deep black colour. Nystatin and Azalomycin F were found to be very effective in treating this disease (Sindermann and Hatai, 1974).
Bacteria - the gills turn orange-yellow or light brown during the initial stages. Eventually the gills turn darker until they are black. Treatment is done by bathing in a 2–3 ppm concentration of furazolidone for two to four nights (Shigueno, 1975).
Black gill disease can retard growth, inhibit molting, impede respiratory processes and disturb ionic and water uptake. It is to be observed that the infected shrimp are thin.
Chitinoverous bacteria are commonly found to infect shrimp in ponds. The infected shrimp can be noticed due to the presence of eroded and blackened body portions. The bacteria typically attack the edges or tips of the exo-skeleton and a progressive destruction of the exoskeleton induces secondary infection which may cause death.
A mixture of malachite green (0.5–1 ppm) and formalin (20–75 ppm) in water, reduce losses from this disease. When incorporated in food, the following were found to be effective treatments: terramycin (0.5–1 ppm); sulfisozole, nifurstyreic acid, and chloramphenicol (Shigueno, 1975; Sindermann, 1974).
In shrimp suffering from muscle necrosis, there are white patches in the tail, or the whole tail is white. This condition is usually associated with stress behaviour such as swimming at the surface or jumping out of the water. It is caused by a combination of high temperature and low dissolved oxygen. The white colouration is caused by degenerative tissue. Some of the shrimp will survive if environmental conditions are improved. Otherwise, massive mortalities take place.
This disease is caused by microsporidian parasites in the muscle tissue or reproductive organs. It is characterized by a white colouration of the infected area. Sometimes, there is a blue-black colour on the back and sides of the shrimp. The disease usually starts at the telson or uropods and works its way forward. There may be some orange or reddish colour due to deterioration of the tissues.
This disease is caused by fungus. Portions of the exoskeleton turn white.
This disease has no visible signs. Stress, such as exposure to insecticides and crowding has been found to encourage development of this disease.
This occurs during handling and harvesting on hot days. The body of cramped shrimp curves and becomes rigid. The real cause of this condition is unknown, but mortality is reduced if shrimps are handled during cold weather (Liao, et al, 1977).
These are associated with poor water quality such as high content of dissolved organic matter. These organisms occur on the outside of the shell and are removed with the shell when the shrimp molts. The best remedy is to improve conditions of the pond.
Ciliate - this is caused by the protozoan, Zoothamnium sp. It typically occurs on the gills. Treatment with a 25 ppm formalin dip has been effective in controlling this protozoan.
Filamentous bacteria - these bacteria occur on areas of the body surface which have many setules and on the gills. Treatment with potassium permanganate at 5–10 ppm for one hour is an effective treatment.
An outbreak of infectious disease may have been brought on by poor water quality, or inadequate diet. Simply adding chemicals to control the disease is not enough. Generally, treatment with chemicals should be used only as a last resort in the control of disease. Most of the compounds found effective in treating the diseases of shrimp have not been cleared for use by health or food authorities.
some of the chemicals may be carcenogenic or they may cause damage to people who handle them
harmful residues may accumulate in the shrimp and cause illness to the people who eat them
the treatment may upset the chemical balance in the pond by affecting useful organisms like nitrifying bacteria
food organisms in the pond may be killed.
Some behavioural characteristics of shrimp could be used to advantage for harvesting such as their movement around the pond at night while looking for food, being stimulated by the water movement, and being attracted to light. Larger shrimps have a natural tendency to swim out of a pond with the water when water is discharged as their natural habit to migrate to deeper waters offshore. Most species of shrimp are active during the new moon and full moon. The periods of greatest activity are normally shortly after sunset and again shortly before sunrise.
Total harvesting is advised only as a last resort when a large percentage of shrimp in a pond are diseased or are dying from bad pond conditions and there is no way to remedy the situation. Partial harvesting can be utilized when there is evidence of slow growth caused by lack of food. Selective harvesting can be used to reduce the number of shrimp in the pond by cropping large individuals and leaving the smaller ones to grow larger.
Partial harvesting is done where only the large shrimps are caught and the smaller shrimps left in the pond to grow. In this programme of selective cropping, it is possible to harvest the larger shrimps before the main crop is harvested, but the female shrimps shall be sorted out for broodstock.
Traps - barrier traps made either of iron frame with nylon netting material of 3 mm mesh size of bamboo is set around the edge of the pond. The opening at the mouth of the trap is adjusted to the correct size so that crabs cannot enter the trap. The wall openings should be large enough so the small shrimps can escape if partial harvest is desired.
This type of trap is used at night and no bait is needed. A small kerosene lamp placed on top of the trap will attract more shrimp. The trap is emptied periodically so that not so many shrimps are left to crowd in the trap as a portion of them may die.
Cast net - cast net is also used and their use is made more effective by setting bait or food in the area to be fished. Lights are used to attract the shrimp if fishing is done at night.
It is better to let in water into the pond before harvesting is started to stimulate the shrimp and get them swimming around the pond.
Bag net - a bag net is installed at the sluice gate and the shrimp are caught as they swim from the pond out with the flowing water. For P. monodon about 90 percent could be harvested by this method, but the draining procedure is repeated for three successive nights. The remaining shrimps are harvested by hand after the pond is totally drained.
Partially draining water - this method of harvest is useful for P. monodon. The water is drained from the pond very slowly until water remains only in the peripheral canals. The shrimps can be removed from the canals by dragging a seine net around the peripheral canal. The shrimps are then caught with scoop nets to concentrate the shrimps in a restricted area.
A bamboo screen can be pushed along the peripheral canal to concentrate the shrimp in a restricted area. The shrimp are then caught with scoop nets. In all cases, final harvest is by hand after all the water has been drained from the pond.
