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J.P. Yaptangco, Jr.1


The objective of the paper is to identify a feasible aeration system which has become a must in the intensive culture of shrimps in terms of cost, dissolved oxygen, conversion efficiency, and the possibility of manufacturing the equipment in this country. Performance of wat pump aerator and paddle wheel type aerator was analyzed and compared. It was observed that the water pump aerator has less operation cost and performs better than the paddle wheel. However, the paddle type is easier to manufacture and can be distributed with less cost. In cognizance of the above findings, it is suggested that the paddle type aerator be utilized until present local manufacturers are saturated. However, future expansion should be geared towards the more efficient water pump aerators.


1.1 The problem and objectives

The use of aerators has become a must with the introduction of intensive culture of shrimps. While you can go out and purchase the available paddle wheel type aerator in the market there is no available data on power input versus dissolved oxygen increase. There is also no available data on the comparison of different kinds of aerators so that an intelligent choice can be made for different applications. This study attempts to answer the above questions and analyzes the possibility of the manufacture of this equipment in this country.

1.2 Assumptions

Experiments were done in a hydraulic laboratory using freshwater. While there may be slight variations, for purposes of this study, it is assumed that the increase in oxygen in freshwater is more or less the same as in water of different salinities given the same treatment.

1.3 Hypothesis

Theoretical computations on all possible types of aerators were done first. The types which show impracticality as to manufacture or use were discarded and those showing promise were experimentally tested in the laboratory. The power inputs were measure and increase in oxygen corresponding measured. All other factors were kept constant. The results were a measure of the efficiency of that particular equipment. This can related to costs per volume of water per increase of dissolved oxygen content. Considering the price of energy today and the almost continuous application of the aerators in intensive shrimp culture the decision on what equipment to use will make a big difference in profits.

1.4 Definition of terms

DOdissolved oxygen
Compressorreciprocating piston type
Blowerair blower — turbo
Water pumpcentrifugal volute type
Paddle wheel type aeratorrotating mechanical paddles
TEFCtotally enclosed fan cooled electric motor
PSIGpressure per square in gauge
CFMcubic feet per minute
SPstatic pressure
DHPdrive horsepower
gpmgallons per minute

1 Practicing Engineer and Officer, Lizares Agricultural Development Co., Valerio St., Iloilo City and San Lorenzo Village, Makati, Metro Manila, Philippines


2.1 Parameters

The aerators were used for intensive shrimp growout ponds in one hectare modules in the farms. Choice of prime movers were limited to small horsepower gasoline or diesel engines or electric motors. Considering that use in most cases was continuous, gasoline engines were ruled out. There are some low speed heavy duty, continuous rating diesel engines. These are however very heavy and bulky. They also vibrate heavily and are not suited to applications without permanent foundations. While applications as prime movers for aerators can be designed they will have to be costly and sophisticated. This leaves electric motors as the ideal prime movers.

Considering that the application is in the water and it involves water sprays the totally enclosed fan motor is a must.

Three-phase electrical connections and big transformers are very expensive and in most cases the utility companies are reluctant to provide either. A low horsepower single phase motor is usually then the choice of the fish-farmer. The three phase, low horsepower is however the ideal choice whenever possible. For the purpose of this study however 1 hp single phase, 1 750 RPM, TEFC electric motors were used.


3.1 Scientific

The researcher has not seen any literature on the subject except engineering books on compressors, blowers and liquid pumps. Their application as aerators has not been discussed.

It is recalled that there was an article in an agricultural magazine regarding the use of aerators in Israel. The aerators were diesel engine driven centrifugal blowers with the large capacities. They were being used only during emergencies when there were fishkills due to DO depletion. They were portable and can be transferred from pond to pond.

3.2 Commercials

There are brochures being given out by distributors of aeration equipment. They recommend two or four aerators per hectare positioned in diametrically opposite corners depending on the stocking density. It is mentioned that these have increased yield from about 1 000 kg per hectare to approximately 3 000 kg per hectare.

There is however a dearth of information on DO content changes due to their usage.

It is also said that the positioning can push solid waste to the center where drainage pipes are installed. The veracity of this claim should be clarified especially the conditions under which this happens.


4.1 Sources of data

One horsepower, single phase, 230 volts, 1 750 RPM, 60 cycles, electric motor was taken as the basis of all power inputs. Computations and estimates were made of the specifications of the corresponding aerators. The equipment found feasible were then tested. The data taken were for the electric motor (voltage, amperes) and for the water (DO content per time).

Eight days waiting were necessary to bring the DO back to starting level after every experiment. The number of trials depended on the results obtained.

4.2 Instrumentation

The experiment was conducted in a hydraulic laboratory. The weir itself was not used but only the catch basin and return tunnel were used.

The measurement of the tank was 2½ m wide, 1½ m deep and 10 m long or a volume at 37.5 m3.

A volt meter from 0 to 300 volts and an ampere meter from 0 to 20 amperes were used for the input.

A titration kit was used to measure the DO.

An ordinary watch was used to measure time.


5.1 The vibrating reed aerator

The vibrating reed aerator commonly used in aquaria has a very small capacity. The input current is in milli-amperes and the capacity below 1 CFM. It will therefore take hundreds of them to aerate a hectare of fishpond 1.5 m deep. The wiring system will also be very expensive and extensive.

5.2 Air compressor

An air compressor has very high head and small capacity. A 1-hp driven electric motor can only give 0.179 CFM at its lowest pressure. It will therefore take a much bigger prime mover to give satisfactory aeration. It is not suited to this application where the static pressure required is low and the volume big.

5.3 Turbo blower

where CFM=Cu ft of air being handled per minute
Static pressure= air frictional resistance or the force tending to compress or expand the fluid

The discharge has to be submerged under water by 1.5 m or 59.04 inches of water. This is the minimum static pressure that must be developed by the blower.

59.04" H2O has a SP of 2.13 PSIG

This pressure however cannot be attained by a single stage turbo blower running at 3 500 RPM. The blower has to have at least 2–3 stages of turbo blowers.

This type of blower is of the low specific speed type which has low efficiencies varying from 30–35 percent. This is quite low compared to single stage blowers.

Assuming that we use a 1-hp electric motor as drive then:

This CFM is too small that the impeller is almost impossible to fabricate specially at a very tiny diameter. There will be almost no opening.

The air blower can then be manufactured for this application only at higher horsepower which is outside the parameters of the study.

5.4 Water pump

The total dynamic head consists of:

  1. Suction lift or suction head in ft
  2. Discharge head in ft
  3. Pipe fruction head in ft
  4. Velocity head in ft

Velocity head in ft = due to water volume

Where V=velocity of water in ft/sec inside the pipe
g=acceleration of gravity
 =32 ft/sec/sec

Water hp = GPM × TDH × 0.0002515

For a pump driven by 1-hp of 1 750 RPM and 15 ft head

The manufacture of such a pump is feasible and shall have a 3" suction and 3" discharge.

A 3" × 3" centrifugal pump was then chosen and the necessary drive installed. The result was a 1-hp vertical electric motor directly coupled to a 3" × 3" vertical centrifugal pump. The pump was slightly submerged in the water for priming.

Pipes with a multi-holed discharge head were installed and the unit was installed for testing.

5.5 Paddle type aerator

where = _ _ _ _ _ _ _ __ _ _ _


An rpm of 60 was assumed

This will pull against its weight and water resistance. A rotating paddle wheel partly submerged in water with this torque is possible to manufacture.

A 1-hp horizontal electric motor was installed with a pulley and chain drive step down transmission system to paddle wheels welded in spokes which are in turn welded to a shafting rotating on sealed prelubricated bearings.

The paddle wheels were adjusted in size until the ampere meter reading read full load.


6.1 Performance of the water pump aerator

  9:15 AM6.5220  
10:00 AM6.5230  
11:00 AM6.5230  
  12:00 Noon6.5240  
 1:00 PM6.5250  
 2:00 PM6.5250  
 DO contentVoltageAmp

6.2 Performance of the paddle wheel type aerator

10:00 AM6.5220   
11:00 AM6.5230   
   12:00 Noon6.5240   
  1:00 PM6.5240   
  2:00 PM6.5250   
  3:00 PM6.5250   
  4:00 PM6.5250   
  5:00 PM6.5250   
 DO contentVoltageAmp

In both cases water from the middle of the length of the tank was used to measure DO. The tank is under a roof.


7.1 Data

The voltage varied a little bit due to the load of the other machines in the factory during working time and no load during break time. The variation however is small and if multiplied by the current will mean 37.5 watts at the most. This is the same for the pump and the paddle wheel. It shall cancel in any case.

The difference in ampere readings however is significant. A difference of 1 ampere can mean 220 watts or 220 watt hour per hour of use. Considering that the aerators sometimes run continuously for days this can mean about 350 kilowatt hours per harvest. Taking into account the cost of electricity which varies from region to region, the difference in cost of inputs can be computed for buying decisions.

7.2 Basis for choice

It took 3 hours and 45 min for the DO to increase to 7 using the water pump aerator. It took 6 hours to increase the DO from 4.6 to 7 for the paddle type aerator. This is very significant and should be noted in choosing equipment.


8.1 Manufacture of water pump aerator

The water pump will need a foundry, machine shop equipment and dynamic balancing equipment for its manufacture. It also needs a hydraulic laboratory with weir and horsepower measuring instruments.

There are however a few pump manufacturers already and as soon as the volume of the demand goes up, some will show up in the market.

The following materials are imported:

  1. Foundry coke
  2. Pig iron
  3. Ball bearings
  4. Stainless steel shafting
  5. Mechanical seals or packing

The following materials are available locally:

  1. Scrap iron
  2. Scrap bronze
  3. Ferro silicon
  4. Limestone
  5. Paint

The manufacture of water pump aerators require much more sophistication than the paddle type aerator and probably not more than five companies in the whole country can manufacture a reasonably good pump aerator.

8.2 Manufacture of paddle type aerator

A small shop with welding equipment and steel shears can manufacture the paddle type aerators. Small shops like this are scattered all over the country and there is always one within a 5 kilometer radius.

Most of the materials are available locally including plastic paddles if they are preferred.

The technology involved is simple and the design can be made through a cut and try method. Once there is a prototype, manufacture is easy.


9.1 Benefits and government policy

From the point of view of the country it is good to have these equipment manufactured locally as it retains the dollar equivalent of the local components. It also relieves the unemployment situation.

However, government policy has shifted to an export-oriented policy. Import substitution like the manufacture of pumps is not now being helped. The prospect of exporting these aerators is nil considering the negative factors of the economic environment compared to other countries.

9.2 Profitability of manufacture

9.2.1 Pump aerators

Cost of raw materials7 100
Cost of labor5 000
Cost of manufacturing overhead2 000
Cost of electric motor900
Direct costs
15 000
Administrative overheadvariable
Marketing overheadvariable
Total overhead
Wholesale price19 900
Gross profit4 900
 per unit less overhead

9.2.2 Paddle wheel type aerators

Cost of raw materials5 100
Cost of labor4 000
Cost of manufacturing overhead1 000
Cost of electric motor900
Direct costs
11 000
Administrative overheadvariable
Manufacturing overheadvariable
Total overhead
Wholesale price15 000
Gross profit4 000
 per unit less overhead

There is no reason why both aerators cannot be manufactured locally with a profit.


Distribution expenses for the paddle type aerators will be much smaller as the small shop owners can also sell them directly. The water pump aerators which has to be manufactured in Manila has to be distributed nationally by a western type marketing organization.

Here is where we can make the Filipino setting work to our advantage. We can use the existing system adding only a product to it.


The whole set-up helps the small Filipino entrepreneurs. The workers of the shop and the shop owner are in import substitution. The aerator users - the shrimp growers are into export. The profits drip down from the top to the bottom.

The setting also is rural. This is the more depressed part of the country and it needs all the help it can.

It has been said and it is possible that this new industry on shrimp culture and related activities may take over from the sugar industry in the Negros provinces.


It is suggested strongly that shrimp growers include electric input and DO readings in their daily data. While this study gives us insight on some aspects of aeration, only field observations can give us definite conclusion and tools.

A longer period of testing is also necessary. The tests were conducted in a factory setting with workers working for only 8 hours. It should be interesting to see the DO in the water intake as the water is saturated.


The water pump aerator cost less to operate and performs better than the paddle type aerator. The paddle type aerator is however easier to manufacture and can be distributed with less costs. The benefits from the paddle type aerator manufacture also affects all the people down the line who needs it. It is suggested, therefore, that the paddle type aerator be used until present local manufacturers are saturated. Any expansion, however, should be towards the more efficient but higher cost water pump aerators.


J. R. Espinosa1


The application of electronics in aquaculture opens a new field in the industry, wherein man and machine, in the unique blend of nature and science can perform a greater task in a much shorter period of time with the least manpower involved. All these could be achieved by the aquaculturist through automation. Furthermore, an excellent comprehensive monitoring and recording system could be adopted to minimize human effort.

In hatchery operations, reduced mortality is an index of success. This percentage of mortality can be reduced through proper electronic control of factors affecting the operations. Harvesting can be facilitated through fish lures and by electrical means. In the processing of products a more sanitary process can be possible if it is untouched by human hands.

The problem of poaching can be detected and prevented through electronic detection and shock treatment. However, the handler of electronics and electrical equipment should be fully warned on the hazards and on proper safety procedures.

With the advent of computerization, farm programs can now be meticulously scrutinized, monitored and controlled. Such computers can be interlaced with the electronic monitoring and control devices to effect a fool-proof operation.


Electronics can be applied in the designing and operation of the aquaculture industry. Consistent with the need to further improve production, electronics can be a very useful tool in accomplishing such goal. This branch of science if incorporated into the aquaculture industry will fall under aquaculture engineering, hence it will be working closely in the planning, design, construction and management of fish farms and hatcheries. The electronic engineer will likewise be working closely with the biologist who will specify the ideal parameters in a given case of culture.

Being a very new form of application, no off-the-shelf devices are available in the market to specifically solve certain aquaculture requirements. The electronic engineer has to combine assorted electronic measuring and control devices available to fabricate new facilities for the industry. The subject of discussion will be based on this premise, enumerating its different possible applications in the aquaculture industry. A combination of these devices will enhance the solution to a given problem. Better automation can be attained through the use of a computer.

Other applications of electronics are on the security and communications aspect in the aquaculture industry.

The different electronic devices which can prove useful in the aquaculture industry can be summarized under the following categories:


    1. Temperature
    2. pH
    3. Salinity
    4. Turbidity


    1. Valves
    2. Flow instrumentation
    3. Blending and buffering system
    4. Disinfection


    1. Hardwares
    2. Software


    1. Sensors
    2. Alarms
    3. Protective and deterrent devices
    4. Communications
    5. Telemetering


1 Practicing electronic engineer and aquaculture operator, Cebu City


2.1 Temperature

Temperature control is very vital in hatcheries. Water temperature where spawning (in the case of shrimp) and egg hatching are to be conducted must be controlled in order to attain maximum results. Ideal hatchery temperature ranges from 28°C to 30°C. This has a proportionate band (PB) of 2°C. Accurate measurement of this temperature and the control of the PB to within 2°C calls for good instrumentation. Electronic temperature sensors such as semi-conductive silicon diode or thermistor can be used. The corresponding variations in temperature is reflected in form of variations on the diodes conductivity. Diodes A and B when forward biased, the voltage drop across will change proportionally to the change in temperature. If the temperature increases, the voltage across the diode decreases (Figure 1). Thermistors behave in the usual manner as that of a diode; thermistors have two kinds of characteristics. The positive temperature coefficient thermistor is one where the resistance change is directly proportional to the temperature change. The negative temperature coefficient thermistor has an indirectly proportional change of resistance with respect to the temperature.

Another usable temperature sensor is the thermocouple. Here two electrical conductors of different material are conductively and electrically connected at a point voltage at the free end of the two conductors.

The electromotive force (voltage) produced in this temperature sensors can be utilized to:

  1. Drive a meter moving coil to produce a corresponding temperature reaching M in Figure 1.

  2. With the use of a PB controller temperature changes can be corrected through pre-heating or buffering (Figure 2).

  3. This analog signal can be interfaced to the computer to feed information to its CPU.

Such application in hatcheries can also be applied to acclimatization of fry prior to shipment or stocking.

2.2 pH

Some measurements of the pH of water which you can make can be helpful in pond and hatchery management. But many measurements of pH will mean little unless you can interpret them in relation to factors in the water causing the readings.

If the pH is below 4.0 or above 11.0 the water will kill the fish. If the pH is between 4.0 and 5.0 fish may not spawn, their growth rate will be slow and it will be impossible to get a bloom by fertilizing the pond. A pH of 7.0 to 8.5 is ideal for shrimp hatchery and is likely to be suited for good production. This is one positive fact that you can determine by monitoring pH alone. The pH can vary in a pond or tank at certain time of day. It can vary in different depths; pH at the bottom can be lower than at the surface. One factor that can influence pH is the calcium carbonate content of water. This is the hardness of the freshwater source that you will blend with the seawater in the mixing pond. The ideal hardness is 20 mg/p as CaCo3. The CaCo3 is very useful in neutralizing the acidity or alkalinity by forming a new compound calcium bicarbonate.

One notes the following reaction, CaCo3 + H2 CO3→Ca (HCO3)2. Calcium bicarbonate is more soluble in water than calcium carbonate. Carbonates in general whether of magnesium or iron are also usable as buffers. From these characteristics of these substances, monitoring and buffering can be done automatically through electronic devices.

The measurement of pH can be undertaken in a flowing or stationary liquid. This instrument consists of a measuring electrode made of thalamide lead encapsulated in glass, a reference electrode, and a resistance thermometer. All this three components are further placed in stainless steel enclosure. A bridge circuit is utilized for continuous determination of pH. Its two channel amplifier converts the high impedance electrode voltage to low impedance in order to operate a moving coil meter, or input for other recording or controlling devices. Figure 3 represents an automatic basic pH correction device. pH correction can be accomplished through buffering.

2.3 Dissolved oxygen

In warm water countries like the Philippines attention is needed towards meeting the oxygen requirement of fish. Warm water has lesser capability of holding oxygen. When there is heavy rate of feeding, with some feeds uneaten, decomposition of feces, dying or dead plankton organisms in water; available oxygen in water declines rapidly.

Detection and immediate action on temperature is needed to safeguard the culture from oxygen deficiency as these two factors are directly correlated to each other. Ideal dissolved oxygen content in hatchery should not be less than 5 mg/liter for the freshwater source.

The principle of operation in oxygen measurement is based on Henry's electrochemical law that there is a definite relation existing on the oxygen dissolved in the electrolyte and the O2 partial pressure of the adjoining liquid phase. Based on this principle, the measuring method of an electrolyte, a silver measuring electrode and a lead measuring electrode, can be used as under certain conditions supplies an electric current to the measuring; recording or control equipment. Figure 4 illustrates how dissolved oxygen level can be controlled automatically.

2.4 Salinity

Seawater differs from freshwater in the quantity and composition of its dissolved solids, most of which are inorganic salts. Salinity is traditionally defined as the total amount of solid material dissolved in 1.0 kg of seawater when all carbonate has been converted to oxide, all bromine and iodine replaced by chlorine, and the organic matter completely oxidized. This amount of solid material is expressed in grams, and salinity is measured in g/kg or parts per thousand (ppt).

Since density varies with temperature and salinity, a convenient way of measuring salinity is the hydrometer method — by keeping the temperature constant. In case of variable temperature, a correction table for different temperatures should be prepared. Measurements and recording of salinity by electronic method can be done on the same principle as that of determining density. This is done by photometric method. The liquid whose density to be measured is passed through a photo-electric cell across which is a constant light source the voltage generated by the photocell is indirectly proportional to the density of the fluid to be monitored. This change in voltage corresponds to the changes in density. This can then be calibrated through a bridge circuit and be expressed as salinity. Automatic control is illustrated in Figure 5.

2.5 Turbidity

Turbidity is the state at which water has been modified by the presence of sediments and other suspended extraneous matter. In seawater, turbidity can be caused by periodic blooms of algae or bacteria. Ordinarily it results from the appearance of particulate matter in the water. Particulate matter is categorized by its size and origin. When they coalesce they become detritus. Turbidity in hatchery farms should be maintained at less than 50 FTU.

The control of turbidity can be accomplished either by filtration, buffering or disinfection. Monitoring of turbidity can be done electronically using a photocell/LED setup.


3.1 Valves (Figure 6a)

Valves are regulating devices which can either stop, allow or limit the flow of liquid, semi-liquid or gas. These valves can either be controlled manually, pneumatically or electronically.

The source of command to actuate said valves is either coming from a person in the case of manual operation or through feedback from a metering P/B controller in the case of pneumatics and coming from a computer through an interface in the case of electronic control.

In the aquaculture industry, valves are necessary in controlling the flow of water and may be buffering solutions or suspensions, say for example in the control of pH or salinity. To reduce same a dilute solution (water) is added to the mixing tanks to produce the correct pH or salinity. A valve can close and open depending on the requirement. A go, no go valve are the plunger type operated by a magnetic solenoid on its stem. A butterfly type of valve can regulate a flow, and this butterfly is operated by servo-mechanism depending on the command of the computer programmed logic. A combination of these principles is also handy, such as the electro-pneumatic, etc. Valves are usually classified in accordance with their actuator, body and trim. Reverse valve action is necessary to safeguard the process against pneumatic or electrical failure. This reverse valve action is handled by a spring set in the actuator, causing the valve to automatically close in the event of aforementioned failure. One requisite is for this valve to have an over-ride, in case you want it opened in the absence of a signal. The override can be direct through mechanical means or as bypass using manually operated valves. The body design is either double seated or straight through. Higher pressure requirement needs the double seat type of body so it will require minimal actuator which contacts the process fluid. An on-off or go-no valve will require the plugs and actuators to move only at a limited distance, while a butterfly has to move forming an arc, thereby needing servo actuators.

3.2 Flow instrumentation

In electronic application, the usual magnetic flow transmitters are very popular. These flow transmitters measure the flow of liquid with a conductivity of 10 micromhos and transmit a proportionate output voltage signal of 1.5 to 30 millivolts AC to a metering device. Such a transmitter is illustrated in Figure 6b.

The measurement of seawater flow in aquaculture operations is not difficult to quantify due to its good conductivity. On site calibration of this flow meter is an easy task as its controller has provisions for calibration in accordance with the type of fluid handled.

In a mixing pond operation where blending and buffering takes places a flow instrumentation is a must in order to quantify the amount of diluent or buffer solution to be added in the tank. Computer system can handle this problem in accordance with the programme given to it.

3.3 Blending and buffering system

The blending and buffering of ponds and tanks usually takes place whenever there is a need to correct variations of a given parametric standard. This can either be accomplished manually or automatically.

Such blending and buffering technique is applicable in the correction of pH; temperature, salinity and turbidity. Aeration can also be classified as blending, inasmuch as you introduce oxygen to the water by air stones or paddle wheels to agitate and to introduce current and wave action. This form of blending and buffering is to correct dissolved oxygen depletion. Electronically this action and interaction can be accomplished through the command of the measuring and monitoring system we have previously discussed in Item 2 above. The command is then feed to a computer input part of information processor. This processor processes such information and gives a command through the interface and to the valves or switches that operates the buffering solution or gas.

3.4 Disinfection

Disinfection is the destruction of pathogenic organisms by the application of physical or chemical agents. Since disinfection is necessary in the preparation of culture media and other critical processes, it is more convenient and economical to employ physical agents.

Physical disinfection can be accomplished by ultraviolet (UV) irradiation or ozonation. The effectivity of UV irradiation is dependent on the size of organisms; the amount of radiation generated and the penetration of UV rays into the water. The bigger the organisms, the more resistant it is to UV. Many bacteria, protozoans and fungi can be killed by irradiating them with 35 000 u W sec/cm2 of UV lamp (Hoffman 1974). UV cannot penetrate water farther than about 5 cm under ideal conditions. UV irradiation is less effective in water that have high concentration of dissolved organic carbon or that are turbid.

Ozonation can be accomplished through an electric discharge ozone generator. To attain maximum efficiency of ozone as a disinfectant a longer contact time is needed. When the ozone generator is working a discharge gap is filled with a diffused glow called corona.


As the name implies the word computer comes from the term to compute meaning to calculate. Earlier computers were referred to as calculators.

In addition to doing calculation and mathematical operations, a computer can perform processes which departs from mathematical aspects. Such tasks as translating texts, adding words to texts, transferring data, bookkeeping, process control and others.

The computer is an electronic device which processes data under the direction of a programme. If the electronic circuitry which executes the tasks is contained on one integrated circuit (IC), this IC is called a microprocessor (Reference, the movie — “View to a kill” — James Bond).

A computer programme is a series of instructions which are executed consecutively in order to achieve a given result. The instruction which a computer can execute are stated in the instruction set. Its control unit directs every activity in and between the various parts of the computer. The control unit has several registers at its disposal, including the instruction register. Programmes which describes in detail the instructions to be executed, is stored in the main memory, so that it can be referred to at will. The data to be processed must be stored in the main memory so it can be processed at will.

The memory function of a computer are divided among the main memory where data and programme are stored; the external memory, used for storing data or programme which can be later processed (magnetic tapes, discs, cassettes, floppy discs and paper tapes and the register).

The most useful programming for microcomputers is assembly language. With the help of this a programme can be converted into machine lades, now ready for operating different electro-mechanical control functions passing through an interface.


The need for security and communication cannot be overlooked in a high capital investment. Man as a major predator in some localities presents a major problem in such set-up as in Laguna de Bay (Figure 8). Water management, coordination, farm management and supervision has some drawbacks and delays causing occasional major losses. This can be minimized through effective communications.

The caretakers and security guard's basic tools are probably a trained dog and firearms. However, a less morbid way of doing it is through sensor, alarm, protection and deterrent devices. Such sensors include capacitive, infrared, sonar, etc. These sensors detect any disturbances. The disturbance is feed into the processor and translated into electrical impulses, which can be utilized to trigger an alarm, protective device or a deterrent device. Alarm and protective systems can be localized in the guardhouse for the security guard to exercise his discretion. The processor can also trigger a harmless high voltage, low current shock treatment similar to the ones used in harvesting. This time you harvest the poacher instead of the fish.

In large pond water management gate closing and opening is critical. Coordinating this operation can be done through portable radio transistor (walkie-talkies). A separate communications set-up of longer range will be used for supervision between caretaker (at pond site) and office (owner's place). Marketing to harvesting traffic are easily coordinated. Several other communications traffic can be handled by this system. On an integrated pond operation where the office, hatchery and ponds are located in one site a direct dialing urban telephone system may be used. This system will interconnect your farm with civilization.

5.1 Telemetering

The advent of monitoring and controlling parameters has been practiced in other industries like long-distance tailings disposal or concentrate transport. In aquaculture telemetering is much applicable for monitoring the culture density in fishpens and cages. Unattended fish cages can be continuously monitored against poachers, its growth rate monitored and other variables you might want to record and observe.


Electricity is one of the most obedient servant of man as long as it is properly treated. Treatment in this case is in the sense that you must also respect its capability to kill a man. Researches concluded that even if the voltage is low it can cause fibrolation and death if the frequency is 60 HZ. A 50 HZ current is less hazardous than 60 HZ. Current passing through your vital organs (heart) from your extremeties are the major causes of death. Avoidance of this occurrence is a must.


Cook, H.L., 1973 Problems in shrimp culture in the South China Sea Region. FAO/UNDP South China Sea Fisheries Development and Coordinating Programme, Manila, Philippines. SCS/77/WP/40.

Carr, J.J., 1982 Microprocessor interfacing. TAB Publication No. 1396.

Gratzok, J.B. and E.E. Brown. 1980 Fishfarming handbook. AVI Publishing Co., Inc.

Hartmann and Braun, Measuring and control instruments.

Hechanova, R.G. and B. 1980 Tiensongrusmee, Report of assistance on selection of site, design, construction and management of the Ban Merbok, Kedah, Malaysia Brackishwater Aquaculture Project. South China Sea Fisheries Development and Coordinating Programme. Manila, Philippines. SCS/80/WP/88.

Dirkson, A.J., 1982 Microcomputers — what they are and how to put them to productive use. TAB Publications No. 1406.

Saffords, E.L., Jr., 1979 The complete microcomputer systems handbook. TAB Publications No. 1201.

Spotte, S., 1979 Fish and invertebrate culture, J. Wiley Interscience Publication.

SEAFDEC Aquaculture Department. A guide to prawn hatchery design and operation SEAFDEC AQD Extension Manual Series No. 9.

Figure 1

Figure 1. Bridge circuit for temperature measurement

Figure 2

Figure 2. Temperature control basics

Figure 3

Figure 3. pH control basics

Figure 4

Figure 4. Automatic compensation of dissolved oxygen defficiency

Figure 5

Figure 5. Automatic control of salinity

Figure 6aFigure 6b
Figure 6a. Solenoid valveFigure 6b. Magnetic flow sensor

Figure 7

Figure 7. Analogy of a computer to human being

Figure 8

Figure 8. Burglar's and poacher's alarm system

Figure 9

Figure 9. Direct dialing telephone system

Figure 10

Figure 10. Electrical safety hazards


P.F. Subosa1


Vital information aquaculturists need to know on lime are: (a) what lime to use; (b) why lime is used; (c) which form to apply; (d) how much to apply; and (e) when to apply.

Experiments on the use of lime in brackishwater ponds at SEAFDEC Leganes Research Station pointed out the need to apply lime at least once a year and the importance of determining the quality of the soil.

Application of 1–2 tons agricultural lime per hectare in extensive shrimp ponds was observed to be significantly effective in improving the pH and hastening the decomposition of organic matter in soil. Considerable water outflows from intensive and semi-intensive shrimp ponds made the lime ineffective. It was observed that liming showed no significant change in soil pH due to this water outflows.

Proper water and soil management plus lime can improve the pH of newly renovated or constructed ponds and peripheral canals.

To eradicate pests and predators, lime with ammonium sulfate is effective as a substitute for synthetic pesticides.


Fish or shrimp usually die in strongly acidic pond waters (pH lower than 5.0). Shrimp usually does not take food when pond water pH is below 6.0 and die at 5.0. On the other hand, fish will survive in waters with pH 5.0 to 6.0, but their growth and reproduction will greatly be affected. There are pond waters with pH within desirable level, but pond bottom soils are acidic. Shrimps which are bottom dwelling organisms could directly be affected by soil acidity resulting in slow growth and low survival. Aside from serving as a substrate for the organisms, soil is one of the main sources of nutrients. Availability of these nutrients is dependent on the pH of the soil and the overlying water. Hence, unless the soil is properly treated, high pond production cannot be attained.

There are many ways of improving water and soil pH. Here, liming may be considered as remedial measure in most ponds to provide the fish population a desirable environment towards higher pond production.


Three types of lime available in the country are the following: agricultural, slaked or burned, and hydrated lime.

2.1 Agricultural lime (CaCO3) or calcite and CaMg (CO3)2 or dolomite

These are commonly available and less expensive than the other two: the slaked or burned and the hydrated lime. A finely ground limestone has a neutralizing value of 100 percent (Table 1). Usually to most fishfarmers these are referred simply as limestone or lime. They are easy to handle and leave no objectionable residues in the soil. The important minerals in limestones are calcite or calcium carbonate (CaCO3) and dolomite or calcium magnesium carbonate [CaMg (CO3)2]. Rate of reaction of dolomite is significantly slower than calcite. Ground limestone has a long term neutralizing ability. Neutralizing power or value of lime is the relative ability of lime to neutralize acidity and is influenced by the fineness of lime. The higher the percent fineness, the better.

1 Officer-in-Charge, Chem-Bio Laboratory, SEAFDEC/AQD, Leganes Research Station, Leganes, Iloilo, Philippines

2.2 Burned or slaked lime (CaO)

This is produced after heating limestone in commercial large kilns. Because of its high neutralizing value the effect on soil and water is instantaneous, and corrosive effects disappear more or less in 2 to 3 weeks. Its disinfectant properties are useful in eradicating pond pests and predators and controlling fish diseases. But it is not easy to handle because of its caustic properties.

2.3 Hydrated lime or calcium hydroxide [Ca (OH)2]

This is the calcium oxide with water. It has similar properties with slaked lime but is more caustic than burned lime. It is not quite easy to handle. Fineness of oxide or hydroxide of lime is always satisfactory.

Burned and hydrated limes react with the soil or water much more rapidly than do the agricultural or ground limestone. This is why caustic materials are more preferred where immediate reaction with the soil is required. If there are advantages, there are always disadvantages. With the burned and hydrated lime, carbonation is likely to occur if the bag is left open and the prevailing air is moist wherein neutralizing efficiency can be affected. Where faster rate of reaction is not a factor, dolomitic limestone is recommended because of the presence of high quantities of magnesium. Where there has been occurrence of disease among fish in a pond, the best means of preventing future outbreaks is by drying and liming the pond.

Fineness also influences rate of reaction of these liming materials. For the finely ground limestone to be effective, 50 percent should at least pass 100 mesh sieve. Fineness is considered an important characteristic if the lime to be used is dolomite. Usually, allowance is made for slow acting material by increasing the rate of application.


Lime is applied in fishpond mainly to correct acidity in the soil and water, and it is the most economical and commonly available substance. Moreover, there are many benefits that could be derived from liming the pond soil. These are the chemical, physical and biological effects.

Biological effects of lime rest mainly on the response of organisms. It however stimulates nitrogen fixing bacteria and other heterotrophic soil organisms, thus promoting the bacterial breakdown of waste materials including green manure and other organic fertilizers. Upon decomposition of these wastes, formation of humus is encouraged. Humus is soil organic matter chiefly of plant origin, which contributes in achieving a satisfactorily granular structure of soils.

Application of lime in soil with a pH 5.0 has desirable chemical effects. It will decrease the concentration of hydrogen ions and solubility of iron, aluminum and manganese. Likewise, the availability of phosphates, molybdates and exchangeable calcium and magnesium will increase. Figure 1 shows the relationships existing in mineral soils between pH and activity of microorganisms and availability of plant nutrients. In short, lime assists in the release of nutrients from the soil. Ponds that favorably need lime are categorically classified into three: a) those containing high amounts of humic substances; b) those with moderately and slightly acidic soils (pH 5.0–6.0); and c) acid sulfate soils (Figure 2).

Identification of the desirability of applying lime depends upon physical and chemical characteristics of the soil which shall be examined first. pH, organic matter and texture shall first be determined from the representative subsoil and surface samples. The samples could be sent to any private or public laboratories that are able to conduct the analysis specified. The final decision follows after all the information are obtained.


There are several factors considered important in choosing what lime to be used, to wit:

1) neutralizing power, 2) cost per ton applied to the pond, 3) rate of reaction with the soil, 4) fineness of the lime, and 5) handling, storage and availability.

Neutralizing power is the ability of the lime to neutralize acid and the strength is expressed in terms of calcium carbonate. This suggests that every 100 kg of agricultural lime has a neutralizing capacity of 100 kg of calcium carbonate (Table 1). This factor together with the cost of lime per ton will give higher neutralizing power for every peso spent. For the purpose of calculation, the cost of applying each ton of agricultural and burned lime to the pond are 800 and 500, respectively. Obviously, 0.56 ton of CaO equal 1 ton of CaCO3 will be 448 for burned lime and 400 for the agricultural lime. Unless a rapid reaction is desired, this reaction suggests that agricultural lime will be considered. Fineness also affects the reaction of the liming material. Fineness of limestone may be considered important especially if it is dolomitic. Allowance will be made for the lack of faster acting material by increasing the rate of application.

It is emphasized that only lime which are cheaper and locally available be used to lessen the cost of production. However, the prerogative rests on the user and the corresponding purposes of liming.


A number of factors affect the amount of lime to be applied in ponds. The factors identified to be considerably and vitally important are: a) chemical and physical properties such as pH, texture, structure and amount of organic matter, b) kind and fineness of lime, and c) cost of lime.

Soil pH will indicate whether application of lime to the pond is necessary. Using laboratory procedures, the lime requirement can be calculated. Lime requirement refers to the amount of lime required to raise the soil pH, say from 5.0 to 7.0.

Texture and organic matter of soil are also important for they are indicative of the absorptive and buffer capacity of the soil. Heavy textured clayey soil has higher buffer capacity and naturally requires greater amount of lime to obtain a desirable increase in pH.

Other factors like fineness, kind and cost have been discussed and their significance are self-evident. With regard to the kind of lime, the three forms can be evaluated based on their respective effects on the soil approximately in the ratio of 1 ton of agricultural lime (finely ground) to 0.74 ton of hydrated and to 0.56 ton of burned lime. If the chemical composition is important, so is fineness. Usually, the supplier has designated a different price with regard to fineness. The coarser the lime, the cheaper it is.

The customary practice is to apply lime at 1 ton per hectare in ponds with higher humic substances and those with moderately acidic soil. To apply more than 4 tons of agricultural lime to a hectare of mineral soil at any one time is seldom practiced unless the soil is strongly acidic. However, the subsequent process of tilling, drying, submerging and washing of pond bottom soils for a few months have practical and economical impact on improving the pH of acid-sulfate soils. But of course, without this soil and water management, one is obliged to employ the use of lime. Nevertheless, this latter method requires higher dosage of lime and could be costly. The data given in Table 2 will serve as a guide in practical brackishwater pond liming. The designation on the degree of acidity and alkalinity of pond soil is shown in Figure 1. Slightly acidic soil pH range from 6.1 to 7.0 while moderately acidic soil ranges from 5.1 to 6.0. Strongly acidic mineral soil has a lower pH, ranging from 4.1 to 5.0. An acid sulfate soil when dried has pH 4.0 or below.

In Figure 1, desirable range of soil pH is 6.5 to 8.0. Alkaline brackishwater will tend to improve the pH of the soil with 0.5 to 1.0 degree increase in pH.

Identification of the desirability of applying lime depends upon physical and chemical characteristics of the soil which should be examined first. The pH, organic matter content and texture will first be determined from the representative subsoil and surface samples. The samples could be sent to any private or public laboratories that are able to conduct the analysis specified. The final decision follows after all the informations are obtained.

The suggested amounts were calculated with the assumption that these rates will be used as initial applications. Smaller maintenance dose may be satisfactorily used after the pH of the soil reached the desirable level (at least pH 6.5).

The lime requirement will be determined from the representative pond soil samples. Usually 1 kg of soil from a hectare pond is required and can be collected by using La Motte sugar sampler or an improvised one from a depth of 15 cm. The representative soil will be immediately mixed and air-dried to make sure that the soils are free from dust and the effects of direct sunlight. Oven drying at 40°C is recommended if available nutrients will not be analyzed.


Application of lime depends on the need of the pond and the purpose of the user. Ponds that require lime are those newly renovated or constructed, older ponds with high content of organic matter, moderately acidic ponds, acid sulfate ponds, and those infested with pests and predators.

Lime should always be added 2–3 weeks before application of chemical fertilizers. Phosphate will react with liming materials preventing it from dissolving immediately and will settle at the bottom. However, by allowing a few weeks interval, reaction of the lime with the soil takes place thus increasing the soil pH and hastening the availability of phosphates. With liming and proper fertilization program, pond productivity will increase. Adding the right amount of lime will improve soil pH to a desirable level for the optimum utilization of soil nutrients and fertilizer, and for the optimum growth of organisms that serve as food for fish and shrimp.

Fishpond soil can be considered submerged soils. Brackishwater fishponds which are generally constructed in the intertidal zone are greatly affected by tidal fluctuations and are exposed to certain changes. Some of the ponds at the Leganes Research Station of SEAFDEC have been in operation for more than a decade. Soils are subjected to environmental and ecological changes. The soil characteristics of the ponds change in time and soil pH is one that is greatly affected. Table 3 shows the periodic change of soil pH in 1.0 ha ponds in LRS. Although these ponds were subjected to proper management practices, decreased soil pH was still obtained as CA-0101 pond in 1982. From 5.9, soil pH increased to 7.4 in 1979, then to 5.35 in 1982. For CA-0105 pond, pH lowered from 6.84 in 1977 to 4.70 in 1979. If this had not been altogether corrected or improved, the acidic state of the soil could have intensified and could have affected production. Thus there is need to monitor soil characteristics at least once or every two years. Application of lime at smaller dosages after every cropping is also recommended to prevent this degraded condition from happening.

If proper attention is given to already developed and established ponds, much more should be given to newly renovated or newly constructed ponds. The problems associated with potential and actual acid sulfate soils are prevalent. The problems are not only on pond bottom soils but also on pond dikes and overlying waters. In February 1982, renovation of 32 shrimp experimental ponds and 12 milk-fish ponds of varying sizes were completed. The soil quality of these ponds were determined. Thirty of these ponds had potential acid sulfate and the rest had actual acid sulfate soils. Soils excavated from the ponds were used as dikes. The pH of dikes were determined after drying them for 1 month. Table 4 shows the pH of the pond bottom soil and dikes. Because of the poor conditions that these pond exhibited, reclamation methods were applied. The ponds were allowed to dry for three weeks, submerged for 1 week and flushed through tidal waters. These processes were repeatedly done for several weeks. After 4 months the soil quality was determined.

Table 5 shows the periodic changes of soil pH after 4, 6, 12 and 25 months. From 44 ponds, only 10 ponds has an increased pH but not to desirable levels. The surface soils (15 cm deep) were then tilled to accelerate oxidation and dried for another 2 weeks. Subsequent drying, flooding and flushing were done. Burned lime was applied after 6 months based upon the lime requirement of the soils. In 1983 after 25 months, all the ponds reached the desirable level of soil pH. This result, however, implies that even after a 4-month reclamation pH may still remain unimproved. Hence, it is important to check the soil conditions to determine whether there are changes or not. Most often one neglects the importance of monitoring soil conditions. Observations showed that even after six months, low soil pH still occurred for sandy, silty and clayey soils. When liming materials were applied, the soil pH increased as shown in the 12th month results of analysis in Table 5. Hence, application of lime resulted in increase in pH.

The renovation or construction of peripheral canals may also present problems. Peripheral canals are usually constructed to facilitate draining of water especially during harvest as well as to increase water depth, particularly in shrimp ponds which have elevated bottom and bigger areas. To further excavate the whole pond bottom could be expensive. Instead, peripheral canals are built, usually about 0.5 meter deep. Soil analysis of 16 ponds in 1982 showed that the pH of the canals was 0.30 to 0.63 degree lower than the elevated pond bottom. To construct canals inside the pond would mean exposing the elements to environmental and ecological changes which may worsen the conditions of the ponds. It is also recommended that steps should likewise be undertaken to improve the canals and applying lime may be the quickest way.

Boyd (1982) reported that liming materials stimulate bacterial action and hasten the decomposition of organic matter. In the study of Hansell and Boyd (1980) on the rates of carbon dioxide release from soil in laboratory soil-water systems, they found that limed soil lost 1.37 percent of its initial carbon during the incubation period. The increases in bacterial decomposition favor mineralization of nitrogen and other nutrients from organic matter. In the experiment conducted on the use of agricultural waste products as fertilizer in 50 m2 ponds, observations showed that limed soils had reduced organic matter content as shown in Table 6. Two tons agricultural lime per hectare was the rate applied. Also the soil pH of the ponds increased. Lime had possibly hastened the decomposition of organic matter and released the available nutrients. It should be noted that in this study water was maintained at 40–50 cm deep. Only 5 percent of the pond water was changed every 2 weeks through tidal water. Application of lime did not only raise the pH of soil but also helped in the release of available nutrients in the soil. Similar results were obtained in another study on integrated farming of Penaeus indicus, Chanos chanos and poultry in 1 000 m2 ponds conducted from September 1982 to January 1983. Limed soils have reduced organic matter content and improved pH. Table 7 shows the increases of pH after applying 1 ton agricultural lime per hectare. In this experiment pond water replenishment was through tidal water with the water depth maintained at 40–50 cm.

The use of 1 to 2 tons agricultural lime per hectare was effective in maintaining and increasing the soil pH of the pond used for extensive shrimp and milkfish culture. Hickling (1982) as cited by Boyd (1982) stated that an application of liming material would indefinitely last in a pond with no outflow. Boyd and Cuenco (1980) also reported that 10 water replacements might be tolerated before liming is again needed. They further added, however, that this does not suggest that a pond may be drained 10 times before applying lime. In LRS extensive shrimp and milkfish culture requires only limited water replacements since natural food is being grown. If ever there is water replacement, it accounts only to 5–10 percent. However, in ponds where shrimps are grown semi-intensively and intensively, water change is almost daily at 10 to 50 percent of the total volume. In these ponds the beneficial effect of lime is destroyed. Table 8 shows the soil pH of 15 shrimp semi-intensive ponds. The 2 ton agricultural lime per hectare did not improve the soil pH from 0-day to 152-day. The same results were obtained from the intensive shrimp ponds as shown in Table 9. A 1-ton agricultural lime per hectare application in these four ponds was ineffective. These observations indicated that liming materials may not be as effective due to considerable water outflow. The lime may possibly be leached or washed out from the ponds. The pH of the overlying waters ranged from 7.74 to 8.5. Salinity ranged from 21 to 40 parts per thousand (ppt). The same semi-intensive ponds were used for the extensive culture of shrimp from November 1984 to March 1985 and the pH of the soil increased to above neutral levels. In this case, burned lime may prove effective. Nevertheless, further studies on the effect of water exchange on lime applied in soil is recommended.

Lime can also be used in eradicating pests and predators. Synthetic organic pesticides have been generally used to eradicate pests and predators. However, their residual effects pose a threat thereby discouraging their use in shrimp and milkfish ponds. Several pesticides have been reported by SEAFDEC researchers to cause softshelling of shrimps. Applying plant-based pesticides could be an alternative; however, they are not yet widely available in the country. In 1981, the researchers of SEAFDEC LRS developed and tested a technique of eradicating pests and predators before stocking. This involved the use of lime and ammonium sulfate (21-0-0). The procedure included draining the ponds and exposing them for a day or two. Burned lime was applied at a rate of 1 ton per ha over the whole pond particularly in wet areas. Immediately after broadcasting the lime, ammonium sulfate at a rate of 10 g/m2 was added in wet areas (holes, root stumps, tilapia nests, canals and gates) as well as areas difficult to drain. The response of fish should be closely observed. Within 20 minutes the fish would die. Eradication is best during calm and warm weather. After the eradication process the ponds may be filled and stocked within a day.

Table 1. Corresponding neutralizing value of lime in percent calcium carbonate

KindNeutralizing value (% CaCO3)
CaMg (CO3)2109
CaSiO3  86

Table 2. Suggested amounts of agricultural lime (finely ground limestone) per 15 cm depth soil of brackishwater ponds

Condition of soil acidityAgricultural lime (ton/ha)
Silty soil1Clayey soil2
1. Slightly acidic0.5–1.01.0–2.0
2. Moderately acidic2.0–4.04.0–6.0
3. Strongly acidic4.0–6.06.0–9.0

1 Silty soil: loam, silt loam, clay loam, sandy clay loam and silty clay loam.
2 Clay soil: sandy clay, silty clay and clay.

Table 3. Periodic changes of soil pH in 1.0-ha brackishwater ponds at the SEAFDEC Leganes Research Station

Rearing pondPeriod

Table 4. pH ranges of pond bottom soil and dike of 44 newly renovated LRS ponds

Experimental pondspH
Bottom soilDike

Table 5. Periodical changes of soil pH of selected newly renovated SEAFDEC ponds

Pond no.Soil texturepH
1Loamy sand3.324.105.195.756.52
2Loamy sand5.125.755.655.556.49
3Loamy sand4.705.074.856.216.60
5Sandy loam4.754.415.996.296.70
6Clay loam5.705.855.195.256.59
7Clay loam6.
9Silty loam5.336.306.206.306.50
10Silty loam5.555.405.416.006.55
14Silty clay5.115.404.905.056.50
15Sandy clay5.424.415.356.556.50

Table 6. pH and organic matter content of soil of 50 m2 shrimp ponds applied with and without 2 tons agricultural lime per hectare + 2 tons organic fertilizers

 Pond0 day
(Before lime application)
90 days
(After shrimp harvest)
 FertilizerpHOrganic matter (%)pHOrganic matter (%)
A— Limed7.242.608.0  1.33
 — Unlimed6.851.996.8  1.89
B— Limed6.683.417.5  1.84
 — Unlimed6.901.746.751.56
C— Limed6.503.567.311.70
 — Unlimed6.951.586.751.19

Table 7. pH and organic matter content of soil from 0 day to 141 days in 1 000 m2 brackishwater ponds applied with 1 ton agricultural lime per hectare

Pond no.0 day141 days
pHOrganic matter (%)pHOrganic matter (%)
15.85  6.607.285.34
46.50  9.126.819.00

Table 8. Average values of soil pH in semi-intensive shrimp ponds applied with 2 tons agricultural lime per hectare

 Pond no.pH
0 day59 days109 days152 days

Table 9. Average values of soil pH in four shrimp intensive ponds applied with 1 ton agricultural lime

Pond no.pH
0 day40 days97 days118 days140 days175 days

Figure 1

Figure 1. Range in pH for most mineral soils

Figure 2

Figure 2. Relationships existing in mineral soils between pH and activity of micro-organisms or availability of plant nutrients. Wide bands indicate zones of greatest microbial activity and most ready availability of nutrients. (After N.C. Brady, The Nature and Properties of Soils. 8th Edition, pp. 388–389).


Maximo Mendoza, Jr.1


Inexpensive engineering solutions applicable to small saltfarms, problems inherent to saltbed construction doubling as fishponds, handling of brine, selective crystallization technique to get high grade salt, crystallization options and harvest flexibility are presented and discussed.

The role that saltbeds can take to provide continuing high salinity requirements of brine shrimp culture is also expounded.


This paper is on small saltfarms whose problems can be traced to their doubling as fishponds during the rainy season. These small saltfarms, without too much expense can be modified into modern ones to increase their production and the quality of their salt, to benefit both the producer and the end-user.

These are originally developed as fishponds, which later were found to be less productive during dry season because of high salinity, and it was discovered that more money could be earned producing salt instead of fish. This, in a way started the commercial production of solar salt, accompanied by series of problems — doubling as fishponds — which remain to this day.

Interest of this writer on this subject covers a period of years since 1940 with a university graduate thesis on soda ash and its industrial solar salt feedstock, the acquisition and development of a 25 hectare saltworks Lease No. 1 in Pangasinan, which later had to be given up; having filed with the Board of Investments (BOI) on its 3rd year of a 1 000 hectare salt project in Sablayan, Occidental Mindoro which was shelved because of financing deficiency; and the work with PCARRD2 and with KKK3 in 1983.


Information gathered with the KKK Project is perhaps the most relevant and significant to this dissertation, confirming the potential of small saltfarms to solve their problems.

The first of such problems is the shift from wet to dry conditions, including fresh water soft muddy beds. Assuming a density of 70–80 percent solids, the beds to be transformed into saltbeds or concentractors, will have to count with fresh water that will reduce the salinity of sea water. Several engineering solutions are applied to this problem.

The second is evaporation. It has always been assumed that evaporation in the present technology is determined by surface of fluids. This is of course not good enough. Although weather information has always included amount of rainfall, it has missed on evaporation, the data we need. Our information gathered through the years in the Manila area, which is relatively the same along most western coastlines in the Philippines is 1 meter per season, starting with a sluggish 1 to 2 mm per day to a maximum average of 12 to 14 mm in May, usually terminated by a 2 to 3 cm rainfall.

1 Practicing industrial engineer, Menrich Chemical Laboratory, 147 J. Ruiz St., San Juan, Metro Manila, Philippines.
2 Philippine Council for Agriculture Resources Research and Development.
3 Kilusang Kabuhayan at Kaunlaran or Livelihood Movement (Program).

The evaporation conditions are not good enough for our purpose because just when we are picking up speed in May we are threatened by salt dissolving rain. What to do about this problem is also solved by engineering solutions that will not depend on surface evaporation but includes capillary effect, and very low relative humidity responsible for indoor drying of the clothesline even at night.

The third is rate of concentration. Percentage solids that continue to increase in proportion to evaporation must reach an optimum sodium chloride saturation point. The present design of fishponds converted to saltfarms allocates a relatively large 90 percent of the total working area for these concentrators/saltbeds. It would therefore be useless for the rate of concentration to transpire simultaneously over the large area, when what is needed is only 10 percent, the area covered by crystallizers. Efficiency in matching the input requirement of crystallizers is another engineering problem that has been solved.

In the given KKK information, it will take only — in the given traversed area 50 percent of actual conditions — 16 days to reach a saturation point of 25 percent solids.

This is an approximate improvement of 400 percent over the present practices taking 70 days. The meaning of this is that salt will start to be produced much earlier. This will also mean that expensive crystallizers which have to be filled with brine to prevent their cracking up, will not function as merely concentrators, but crystallizers from the start.

Selective crystallizers is not new but can be applied to separate unwanted solids before sodium chloride saturation point when pure sodium chloride separates. The other dissolved salts in solution not having reached their own saturation point can be separated with the mother liquor or bittern.

This is the technology used to produce 95 to 99 percent sodium chloride which is needed and often imported by our chemical and food processing industries. Meanwhile, the usual market of 80 to 85 percent can continue to be produced so that more salt is produced from the usual 50 tons to 58 tons just working on the selective crystallization technology.

There is continuing argument when and how to harvest, or how large the salt crystals are allowed to grow because of the constraints to adverse rainfall ending the saltmaking season. This is not a conjecture problem but objectives to be computed by qualified engineers who can give the best answer from which a choice can be made by the entrepreneur.

Altogether, using the combination of solutions, it is safe to assume that the present harvest can easily be doubled from 50 to 100 tons per hectare, which should not be a surprise when we consider that we are actually extracting this quantity from more than 250 tons of sodium chloride in more than 10 000 cubic meters of sea water being processed each season.

Going around SEAFDEC we are informed that something is already being done about brine shrimp culture and the only problem is when the program is terminated because of the rainy season. This of course presupposes that all systems are already under control to make the technology work, only to be interrupted by the absence of fresh source of concentrated brine. This should not be the case, because precisely, with engineering solutions applicable even to small saltfarms, it is possible to supply this requirement to maintain production of Artemia the whole year round without interruption. All that have to be done are the requirements of any brine shrimp business in total concentrated brine inputs — year round — and undoubtedly the engineers can supply more than the requirements.

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