Shrimp hatchery

Shrimp Hatchery INTRODUCTION

Shrimp is a valuable aquatic food resource high in protein and commands good export markets. It has become the main target commodity for aqua farming in recent years. Traditionally, shrimp fry are trapped and held in ponds and later collected by shrimp gatherers for stocking in grow-out ponds. With increasing demand for shrimp, supply of wild fry for the increasing number of shrimp farms has become insufficient and inconsistent. The breakthrough in the completion of the life cycle of commercially important shrimps in captivity, such as the tiger shrimp (Penaeus monodon), the Japanese kuruma ebi (P. japonicus), the eastern shrimp (P. orientalis) and the banana shrimp (P. indicus or P. merguiensis), has greatly enhanced mass production of shrimp fry under hatchery conditions. The excellent growth performance of these hatchery-bred fry in grow-out ponds strongly shows that the shrimp hatchery can answer the industry needs for ample supply of shrimp fry for farming.

Importance of this Study:

At the end of this assignment we will know how to:

To construct an ideal shrimp hatchery. To maximize production with minimum investment. Various types of shrimp hatchery found in world. Layout and design variation of a shrimp hatchery. Essential components and infrastructure of a shrimp hatchery.

SHRIMP HATCHERY

A shrimp hatchery is one of the locations where shrimp are kept during their lifecycle development on the way to becoming fully-formed shrimp for commercial sale. Shrimp hatcheries can be found in any region where the shrimp industry is active, and some regions have numerous hatcheries supplying large farming operations. People can also make their own shrimp hatchery out of common materials, to grow their own shrimp at home.

SUCCESS OF SHRIMP HATCHERY

From many years of accumulated experience and research findings, the success of a shrimp hatchery depends on:

The choice of a suitable site Effectiveness and efficiency of the hatchery design Experience of hatchery technicians Efficiency of operational management

SELECTING SUITABLE SITES FOR A HATCHERY

Prior to the establishment of any shrimp hatchery, it is of primary importance to carry out a thorough feasibility study to determine the suitability of the proposed site. The main criteria followed are water quality, availability of spawners and site accessibility.

For establishing large-scale modern hatcheries, the criteria for hatchery site selection must be rigidly followed because it is costly to change site when high financial inputs have already been committed. However, site selection for smaller hatcheries are less rigid than the bigger ones.

Criteria in the selection of a suitable site for a hatchery

1. Sea water supply

The sea water used in a hatchery should be clean, clear and relatively free from silt. The water quality should be stable with minimal fluctuation in salinity. Suitable sites are usually found in sandy and rocky shore ecosystem where there is clean, clear and good quality sea water all year round. Sites not suitable for hatchery are swamps and muddy shores where the water becomes turbid during heavy rains or due to turbulence. Avoid river mouths where abrupt lowering of salinity often occurs during heavy rainfall. An added advantage of rocky and sandy shores is that good quality sea water is relatively near the shoreline thus reducing the cost of piping installation and pumping cost. The hatchery site should also be free from possible impact from any inland water discharges containing agricultural or industrial waste.

2. Availability of spawners

Presence of spawners at the vicinity of the proposed site is of considerable advantage in ensuring consistent supply of spawners, reducing the cost of transportation which could affect the rate of spawning.

3. Availability of power source

Electricity is essential to provide the necessary power to run equipment and other life support systems in the hatchery. Although some marine pumps and aerators can be driven directly by handy generators, the shrimp hatchery can therefore be operated in areas without electricity supply. However, it is more economical to operate it in areas where there is a reliable source of electricity. Installation of an on-site standby generator is absolutely necessary especially in areas where there are frequent lengthy power failures and fluctuations.

4. Freshwater supply

Freshwater is essential for daily hatchery operation such as salinity adjustment, equipment maintenance and for domestic use.

5. Accessibility

Ideally, a hatchery should be sited in areas where there are active shrimp farming operations so that the shrimp larvae produced can be easily transported and distributed to the grow-out ponds. Hence, the site chosen for hatchery establishment must be easily accessible to facilitate communication and transportation.

6. Climate conditions

A hatchery can be established in any climatical condition. However, all the commercial hatcheries take full advantage of nature in terms of energy source and supply of good quality water. Sunlight is the basic requirement for hatchery operations especially in the mass production of natural food used as feeds for the growing shrimp larvae. In the temperate region where adequate sunlight is only available in certain periods of the year, hatchery operations are usually confined to a certain suitable season. In such situations, hatchery production is relatively limited to a short period of time. The optimal temperature for hatchery design may be necessary in areas where there are pronounced long period of rainfalls which often reduces the intensity of light, cause turbidity in water supply and lowering of water temperature.

HATCHERY DESIGN AND CONSTRUCTION

Basically, there are two hatchery systems being adopted. The large-tank hatchery which was developed in Japan is still the popular system applied in many Asian countries such as Taiwan, Thailand, Philippines and Indonesia. The small tank hatchery which originated from Galveston USA, has been applied in the Philippines and to same extent in Malaysia and Thailand. Recently a modification of the above systems has been developed which combined the beneficial characteristics of both systems taking into consideration the limitation of spawner supply.

There are three determinants in designing a hatchery viz: target species, production target and level of financial inputs. Although multi-purpose hatchery design for shrimps and finfish may not necessarily be the same. In any case, the target species must be clearly identified before designing the hatchery.

Production target can be determined based on a market demand and financial input. In the case of species such as P. monodon at which the production of fry depends on the availability of spawners from the wild, production target is limited by the supply of spawners. This limits the production capacity of the hatchery. Whereas in P. japonicus and white shrimps at which spawners are easily available, production capacity is unlimited. Tank capacity up to 2500 cubic meters can be seen in many large-scale hatcheries in Japan where P. japonicus is the primary species grown. However, in most Southeast Asian countries where tiger shrimp forms the target species for hatchery production, tank capacity is considerably reduced due to limited spawner supply from the wild.

Hatchery design is aimed at achieving the production target which determines the size of the hatchery. The tank capacity is based on an approximate ratio between algal culture tank and larval rearing and nursery tanks. Desirable algal tank capacity is 10–20% of the larval rearing tank capacity. The capacity of maturation tank depends on the number of spawners needed.

Size of hatchery

Generally, the size of a hatchery should be based on its functional requirements and economic efficiency. Based on the level of operation, production output and financial investment, hatchery practice can be broadly grouped into three categories viz: small-scale, medium-scale and large-scale hatchery. The major characteristics of each group are shown in Table 1.

1. Small-scale hatchery

This is a “backyard” hatchery usually owned and managed by the shrimp grower himself using family members or immediate relatives for additional labour. The main goal is to supply his own shrimp farm with the required number of fry and the excess may be sold to neighboring growers. Usually the hatchery site is an extension of the farm house with floor space ranging from a few square meters up to about 1000 square meters. In such hatchery operation, the total production capability seldom exceed 5 million postlarvae per annum and the hatchery is operated by not more than 2 technical personnel. In Southeast Asian countries, such hatchery entails a capital investment of not more than US$30,000 and operational cost of less than US$10,000.

Table 1. CRITERIA FOR CLASSIFICATION OF SHRIMP HATCHERIES

Item Small Medium Large

1. Ownership and operation set-up

Family members serve as hatchery workers

Small cooperative

Big corporations, national agencies

Fry for self-use Supply fry to members

Fry for commercial purposes

2. Area or extent covered

Usually using the backyard area

2000–5000 sq.m. 5000 sq.m to 1 ha.

3. Amount of production 1–5 million/year 10–20

million/yearMore than 20 million

4.Number of employees or technicians

1 technician,2 workers

3 technicians,3–4 workers

3–6 technicians6–10 workers

5. Total tank capacity 20–100 tons 100–1000 tons More than 1000 tons

2. Medium-scale hatchery

This type of hatchery is relatively larger than the small-scale hatchery in terms of capital investment, hatchery size, production capability and scale of operation. While hatchery management is somewhat similar to that of small-scale hatchery, the production capability range between 10–20 million post-larvae per annual and is operated by about 3 technical personnel and 3–4 labourers. This type of hatchery is usually put up by small cooperatives to supply the required shrimp fry to its member growers. Private enterpreneurs or government agencies may also establish hatchery of such operational scale to produce fry of sale or distribution to the growers. Capital investment in Southeast Asian countries for such hatchery ranges between US$30,000 to US$100,000 and operational investment of not more than US$50,000.

3. Large-scale hatchery

This scale of hatchery is commercially run by big corporations, national agencies or cooperative projects. While the capital and operational investment far exceed that of the medium-scale hatchery, production capability of such hatchery usually exceeds 20 million post-larvae per annum. Such hatchery is centrally and systematically managed and is supported by a pool of not less than 6 technical personnel and 6-10 labourers. Capital investment and operational cost are over US$100,000 and US$50,000 respectively.

Hatchery facilities

In designing a hatchery, ample space should be provided for the rearing and support facilities needed in the operation. A functional hatchery should have the following essential components-

1. Maturation tanks

The major constraint in hatchery operation of tiger shrimp is the limited supply of spawners from the wild. Hence, eyestalk ablation techniques can be used to augment the scarcity of spawner supply. Thus, maintaining ablated shrimp in maturation tanks would ensure a constant supply of gravid females.

The shape of maturation tanks can either be circular, rectangular or oval. The tank capacity may vary from 5 to 40 tons with depth ranging from 1.2 to 2 meters. If the shrimps are kept for less than 5 weeks, bottom substrate is not needed in the tank. The tank is installed with an inlet pipe from the wall and a double cylinder standpipe at the center for drainage. This system facilitate continuous flow-through of sea water.

2. Spawning tanks

Spawning tanks should be circular with a flat or conical-shaped bottom. Water holding capacity may vary from 50 liters to 1.5 tons. The tank can be made of fiberglass, Plexiglass, plastic or marine plywood. The tanks are used to temporarily hold the gravid females until spawning.

3. Larval rearing tanks

Two types of rearing tanks are being used to rear the newly hatched larvae. In Japan and Taiwan, larger tanks with a capacity of more than 50 tons are being used. In Southeast Asia, most of the hatcheries use smaller larval rearing tanks of about 3 tons capacity.

3. i) Small Tank System

The larval rearing tank may be circular, rectangular or oval in shape with tank capacity ranging from 0.8 to 3 tons. The bottom of circular tanks may either be flat or conical. Rectangular or oval-shaped tanks always have flat bottom. The circular tank is usually 1.8 m in diameter and 1.2 m in depth with a central double cylinder standpipe drainage system which can be used for continuous flow of sea water when the larvae reach mysis or post larval stage. Rectangular tank is about 1.5 × 5 × 1 m in size. The drainage pipe is set at the side of the tank. The drain pipe is also used for harvesting. In all types of tanks, sea water is delivered into the tank through an inlet pipe installed at the top of the tank.

3. ii) Big Tank System

The tanks used are rectangular or square in shape with capacity varying from 50 to 2000 tons or more (5 × 5 × 2m or 20 × 50 × 2m). The tanks can either be located outdoors or if located indoors, transparent roofing should be provided to allow for sources of sunlight .In a big tank system, spawning, hatching and larval rearing operations are done in the same tank. The larvae are reared for 35–40 days (PL25-PL30).

4. Live food culture tanks

In mass cultivation of live food organisms, size of tanks used usually ranges from 1 to 20 tons. The tanks can be made of either fiberglass, polyethylene, marine plywood or concrete. On the average, the total tank capacity for live food culture is about 20% of the total tank capacity for larval rearing.

5. Water storage and filtration tank

The water storage tank is normally elevated to effectively distribute water by gravity to the hatchery. The water storage tank capacity should be at least 20% of the larval rearing tanks. Storage tanks are normally constructed out of reinforced concrete to withstand the water pressure.

When the water is turbid, installation of a filtering screen and sand filter unit becomes necessary. The filter chamber may be constructed adjoining the holding tank. There are two types of filter systems: (a) gravity filter where water is pumped into the filter chamber over the

Fig 01: Water storage and filtration tank

surface of the filter bed and allowed to pass through the filter material by gravity to the holding chamber which is located under the filter chamber and (b) reversing filter, where water is pumped directly to the space under the filter chamber and pumped upward through the filter to the surface and on to the holding tank. In both systems, the filter chamber usually contains either white sand, charcoal, gravel, or all the three as filter material. The advantage of the reverse system is that water pass slowly through

The filter material and the whole surface area of the filter is utilized. It is easy to backwash by spraying water from the surface of the filter and the detritus underneath are easily washed out. On the other hand, gravity filter method allows water to pass through the water chamber too fast and do not fully utilize the surface area of the filter unless it is provided with a pipe spray water over the whole surface area. The disadvantage of the gravity filter system is that the filter is easily blocked.

With detritus after a few days of operation resulting in turbid water and difficulty in back-washing.

Aeration

Aeration is essential during the entire larval rearing process in maintaining sufficient dissolved oxygen concentration in the water, ensuring even water temperature throughout the water column through turbulence and also help reduce the ammonia content in the water.

Aeration may be provided with a roots blower, rotary blower or an air compressor. A blower provides large volume of low pressure air while an air compressor provides small volume of high pressure air. An air blower runs continuously while a compressor which is equipped runs with the pressure tank whenever

The pressure is low. The compressor automatically switches on when pressure drops below a pre-determined level. In a hatchery, low pressure air available at large volume is more desirable than high pressure air at small volume. Moreover, the hatchery tanks are seldom more than two meters deep. Rotary air blowers are not designed for oil free operation and have a tendency to blow oil particles into the air line producing oil slicks on the surface of the water. Air filters at the inlet and outlet pipes are therefore needed. When the capacity of an air blower is less than 10 HP, ordinary air filters for automobile may be used at the inlet pipe, however, for blowers with high horsepower ratings, synthetic foam can be used. Adjustable pressure tank with resin glass beads or Bagasse as filter materials are used for the outlet pipes. The roots blower is more

Fig. 02: A gravity water flower

appropriate for hatchery purposes because it seldom breaks down, less complicated to use and does not produce oil slicks.

In culture tanks with depth less than 2 meters, an air pressure of about 0.2–0.3 kg/cubic centimeters and a volume of 4–5 liters/m2/minute is sufficient to oxidize the dissolved organic matter in the tanks.

Since continuous aeration is essential to the survival of larvae in high density, any prolonged power interruption would seriously affect the culture organisms in the tank. Thus, it is essential to install an automatic switch which starts a standby generator whenever there is a power failure. A battery operated warning device to signal the crisis and the required operation of the standby generator can also be used.

Marine pumps

Centrifugal and submersible pumps are commonly used in hatchery operation. Centrifugal pump is more desirable in the big hatchery because it has a higher total head capacity (Total head is the difference in elevation between the surface of the source of water and the point of discharge).

The selection of the size and type of marine pump depends on the size of hatchery and the daily water requirement. For the small or backyard hatchery, a submersible pump with a discharge pipe diameter between 1" to 4" and a discharge capacity of 6–20 tons/ltr is sufficient to provide the water needed. Medium and large hatcheries normally use centrifugal pumps. The size of the pump depends on the total water requirement per day and the maximum pumping time. The power required can be calculated with the following formula:

Where Pm = output prime mover (kw)

Fig. 03: A Roots Blower

r= specific gravity of water to be handled (gm./am) is normally 1.0

Lay-out and construction

Once the project site is selected and production target defined as an aerial survey of the proposed site will help to determine the perimeter of the area. An aerial view would show the important topographic characteristics such as rivers, shoreline, mountain and low lying plains. A master plan of the hatchery is then made. Lay-out of the hatchery should provide a schematic design of the location and integration of various facilities such as buildings, broodstock tanks, larval rearing tanks, nursery tanks, spawning tanks, pump house, air supply and power house, laboratory, staff house, piping for water supply and drainage canal. The lay-out plan should include the exact dimension, locality, shape and size of said facility. Examples of a simple lay-out of small, medium and large scale hatcheries are shown in figure-

Fig. 04: Layout of medium scale hatchery.

Fig. 05: Layout of small scale hatchery

Technical drawing should show the detail structure of the facility and size and quantity of support materials needed to ensure stability of the facility. From the technical drawing, the owner can roughly estimate the cost of construction. Since the technical drawing presents details of the structures such as thickness of the tank wall, amount and size of iron bars and mixing proportion of concrete, the price of these materials will be easy to canvass to arrive at the cost estimates. However, estimations of construction costs should be done item by item, before making the total estimation. In the total estimates, labour cost should be included.

PREPARATION OF BROODSTOCK FOR SPAWNING

Inadequate supply of spawners remains as one of the major constraints in the development of the shrimp farming industry especially for species such as the tiger shrimp, Penaeus monodon. Recent success in eyestalk ablation techniques has greatly enhanced constant supply of spawners through ablating captive broodstock to maturation. At the present time, the supply of broodstocks and spawners still depend on captures from the wild.

1. Conditioning of broodstock

Upon arrival in the hatchery-

The broodstock are first acclimatized in holding tanks for 4–7 days. The holding tanks should be big enough to provide proper space and aeration. 60% of

the water in the tanks is changed daily. Once the animals have recovered from transport stress, they are induced to molt by

manipulating salinity of water in the holding tank.

The salinity is decreased by about 4–5 ppt for two days and then increased to the normal salinity of the seawater. Majority of shrimps will molt after changing salinity. Mating occurs during this time when the females are newly molted. The shrimps are then ablated 2–3 days after molting or when the shell is completely hardened.

2. Induced maturation

Only suitable broodstocks are used for eyestalk ablation. The criteria are:

Complete appendages Presence of spermatophore in the thelycum of females Size should at least be 100 gm.

Presently, the most practical way of inducing maturation is by unilateral ablation of either right or left eyestalk of the female. Ablation is done by using a razor blade to cut/open the eye, then squeezing out the eyestalk from the base to the tip with the thumb and forefinger or using the fingers alone to break and squeeze the eye. The ablated animals are stocked in maturation tanks at a density of 5–6 per square meter and a sex ratio of one male to one female.

Maintenance of broodstock in maturation tanks

The broodstocks are fed with squid, mussel or cockle meat or pellet feeds at the rate of 10% of total biomass. The water in the tank is allowed to flow through continuously or changed daily at 60–70% of total capacity.

Sampling

Gonadal development of an ablated female is checked 3–5 days after ablation while checking for gravid females is carried out every other day. Sampling and checking are done at night or at any time if the tanks are sufficiently covered and kept dark. During sampling, an underwater flashlight, tied to a pole is held close to the shrimp so that the light strikes perpendicularly on the dorsal part of the body where the ovaries are located. Water in the maturation tank can be lowered to 30 cm to allow the worker to get inside for closer observation. Only gravid females with stages III or IV ovaries are collected and transferred to spawning tanks.

Larval Feed

Under natural conditions, penaeid shrimps are either omnivorous scavengers or detritus feeders. In general, shrimp larvae feed on phytoplankton, detritus, polychaete and small crustaceans and their food preference changes with age. They start feeding at protozoea stage. Protozoea and early mysis stages prefer phytoplankton .At mysis and early postlarvae, food preference changes to zooplankton such as rotifer or brine shrimp. As the larvae grow older than P6, feeding habit changes again to that of a bottom feeder. Polychaetes, chopped mussels or cockle meat are fed during these stages.

Large-scale production of phytoplankton for larval rearing can be obtained in two ways: by direct fertilization of seawater in the rearing tanks or from pure culture. Many hatcheries

depend largely on brine shrimps to feed their growing shrimp and fish larvae. Brine shrimp (Artemia) eggs are sold commercially but the quality varies with the trade brand representing different strains, geographical origin and processing methods. The rotifer, Brachionus plicatilis, is the most important zooplankton utilized as live food for various cultivable marine animals. Dry acetes diet and egg custard are also used as larval feed.

In addition, many other types of feed have been developed and tested as part of penaeid shrimp larval rearing strategies. These feed may either be frozen or dry material from molluscs, crustacean tissue, soy bean cake, soy bean curd, egg mustard and fertilized eggs or oyster. Other types are available as formulated diet or the newly-developed microparticulate and microencapsulated diets. However, the choice of a particular feed used should be properly evaluated based on the following criteria-

Availability and ease of handling (including technical support); Feed performance; and Feed cost and rate of return on capital.

The basic feeding strategies regarding the type of larval feed in penaeid shrimp hatchery employed to date are summarized as follows:

Use of mixed diatoms through direct fertilization in combination with dry or fresh feed material such as soybean curd, soy bean cake, fertilized oyster eggs followed by live food organisms such as rotifer, artemia nauplii.

Use of mixed diatoms through direct fertilization and/or pure culture diatom followed by rotifer and Artemia nauplii.

Use of mixed diatoms through fertilization and/or pure culture of diatoms in conjunction with fresh/frozen mollusc and crustacean tissue.

Use of mixed diatom through direct fertilization and/or pure culture of diatoms in conjunction with other dry feed materials or formulated diet.

Exclusive use of microencapsulated or microparticulate larval feed. Exclusive use of wet or dry product of crustacean tissue.

PREPARATION OF FACILITIES FOR SPAWNING, HATCHING AND LARVAL REARING

Preparation of basic facilities such as spawning tanks, hatching tanks, larval rearing tanks, water supply and aeration systems is one of the most important activities in any hatchery operation. Hatchery production declines if maintenance and preparation of these facilities are not well done.

Tank facilities

Spawning, hatching, larval rearing and nursery tanks are basic requirements in any hatchery and preparation of such tanks prior to operation are accomplished in two ways:

1. Newly constructed hatchery

Tank facilities especially concrete ones in a newly constructed hatchery must be conditioned first before any hatchery operation is done. Alum (Potassium aluminum sulphate), a cheap chemical, can be used to neutralize tanks. The newly constructed tanks are first filled up with sea or freshwater, small pieces of alum are then broadcasted into the tanks at a rate of 250 g/cubic meter and allowed to stand for about one week. Fiberglass or wooden tanks can be conditioned by filling up with water until the pH of the water in the tanks are stabilized.

2. Operational hatchery

Occasionally, larvae in operational tanks get infected by diseases. To deter such occurences, tanks must be properly cleaned with freshwater, dried and exposed to the sun for at least one day prior to stocking. After every run or every other run of operation, the tanks should also be disinfected with 12% sodium hypochloride solution at the rate of 200 ppm for 24 hours. When the tanks are ready, filtered fresh/seawater is introduced and aeration is checked especially in the spawning and hatching tanks. Strong aeration is necessary to float shrimp eggs owing to its demersal nature. If aeration is not strong-enough, eggs will sink and mix with the scum at the bottom resulting in low hatching rate.

Water quality and supply

Water, being one of the most important factors in hatchery operation, must be regularly monitored for important physico-chemical parameters, viz: salinity, pH, N-NO2 temperature. Often times, turbid water flowing out from the sand filter is bacteria laden. This occurs when detritus, small organisms and dirts pass through the filters under high pressure. To avoid this, initial water passing through the filter must be drained off for about 20–30 minutes or until water becomes clear. Disinfection of the sand filter with 12% sodium hypochloride solution at least once a month will help in keeping the filter clean.

SELECTION OF SPAWNERS AND EGG COLLECTION

Although spawning occurs throughout the year among tropical species of shrimps, there are distinct periods of the year when majority of the shrimps spawn. In the case of P. monodon in Southeast Asian waters, there are two pronounced spawning season, from December to March and June to September with only one pronounced period, viz: June-September in the case of P. merguiensis and P. indicus.

While spawners of these species of shrimps are supposedly available all year round, they are abundantly caught during the spawning season.

A gravid female can be easily recognized by the presence of a very large and distinct diamond-shaped dark green mass of ovary between the first and second abdominal segment below the

dorsal shell. Selection of spawners can be easily done by holding the animal with its ventral body facing a light source The criteria used for selecting spawners from the wild are:

Stage IV ovary Complete appendages The back is not broken Presence of spermatophore underneath the thylecum; and The color of the shrimp especially P. monodon should be pink with a faint greenish tint.

Spawners which are slightly reddish could be due to stress caused by abrupt lowering of the water temperature during transportation by fishermen who try to delay spawning. Stressed spawners give very low spawning rates.

Procurement and transportation of spawners

Spawners are usually collected by professional fishermen. In Japan, hatchery operators can easily procure spawners from fish markets because fishermen bring them back alive as live shrimps are preferred by consumers over dead ones. In other Southeast Asian countries, however, hatchery operators must deal directly with fishermen, provide them with the necessary facilities (e.g. containers, battery operated air pumps, etc.) and teach them handling techniques to ensure getting quality live spawners. In order to do this, hatchery operators must have comprehensive knowledge of the operating gears and the means of transporting spawners. In cases where spawners are available only during a certain spawning period (e.g. 3–4 months in P. orientalis) hatchery operators should carefully plan the hatchery operation to meet their requirements.

There are several ways by which spawners are transported from the field to the hatcheries. They can be transported in-

Live fish holding compartment in the boat with running water system (very convenient for hatcheries close to the fishing ground).

Holding tank with aerated seawater at controlled temperature (22–24°C) using ice in plastic bags and transported by trucks.

Plastic bags injected with oxygen and packed in styrofoam boxes. The water temperature can be controlled by using ice mixed with sawdust. In this case, the rostrums of shrimps could be covered with plastic caps to prevent puncturing of plastic bags, and

Bamboo or PVC tubes: the spaweners are immobilized in separate tube without overstraining them. While transporting in boats, the shrimps are held in cool (22–24°C) aerated water in tanks but are transferred to plastic bags with oxygenated water while transporting on land. Tube transport along with reduced temperature reduces the frequency of untimely spawning in transit and/or injuring themselves.

Treatment of spaweners

Upon arrival, each spawner is nowmally placed directly in a spawning tank without any further treatments. However, during winter or when there is known spread of disease, spawners are usually treated with either (a) Treflan (trade name), 0.5–1 ppm (b) KMnO4, 3ppm or (c) Formalin, 25 ppm for 10–15 minutes.

Spawning activity

In nature, adult shrimps mate after the females have molted. Spawning usually occurs while swimming with the spermatophore in the thylecum and eggs are released from the genital pore which is located at the base of the third pereiopod; sperms are likewise discharged into the water through an apperture at the base of the fourth pereiopod. Fertilization is external. Spawning usually occurs between 0200 to 0300 hours at water temperature and salinity ranging from 25 to 30°C and 28 to 32 ppt, respectively.

Egg collection and treatment

After spawning, the animal is removed from the tank the following morning. The eggs are then cleaned either by siphoning into egg collectors or draining 2/3 of the water through a filter net that effectively retains the eggs within the tank . When draining is completed, the scum is then removed using a scoop net with a mesh size bigger that the shrimp eggs. (Fig. Collection of egg) The tank is then filled up with new seawater During the cold season, fungus and bacteria are likely to infect the eggs during incubration. Preventive treatment normally consists of dipping the eggs in 1 ppm of methylm ene blue or 0.5 ppm of malachite green for 10 minutes or 3 ppm KMnO4 for 30 minutes. After that, the eggs are transferred to a cleaner tank for further incubation and subsequent hatching. From the incubation/hatching tank, samples of eggs are counted to determine the number of eggs spawned per female.

Hatching and Transportation of nauplii

Eggs of most species of shrimps within 12–18 hours after fertilization at temperature and salinity range of 26–30°C and 30–23 ppt, respectively.

1. Determination of hatching rate

The density of nauplii is estimated a day after hatching. Nauplii from three 100 ml water samples taken from the spawning tank are counted and averaged. The total number of nauplii in the tank is then obtained by multiplying the volume by the average density.

To determine the hatching rate, the following formula is employed:

Nauplii are then directly transferred to larval rearing tanks.

2. Transportation of nauplii

At the nauplii stage, the larvae hardly feeds and thus depends on its yolk for development. This stage is easy to transport even for long durations. In some cases, where the site of the established hatchery is far from the spawner collecting areas, it is more advantageous to transport the nauplii instead of the spawners which are more prone to stress.

The nauplii are transported to the hatchery in two ways:

Plastic containers - Only strong and healthy larvae should be transported. This is done by concentrating the nauplii at the water surface with a light source at night, gather them by scooping with a plastic or glass container. The larvae are then transferred into plastic jars which are half-filled with seawater. The container is then gradually filled up. A 20 liter plastic container can contain a maximum number of 500,000 nauplii. The open end of the container must be properly sealed to prevent leakage. The survival rate after 6–8 hours during transportation is more than 50%.

Plastic bags - Each bag containing about 6–8 liters of water can be stocked with 200,000 nauplii. The water in the bags are oxygenated and the open end is closed with rubber bands. The survival rate is about 80–90% if transport takes about 4–6 hours .

Larval rearing

From the spawning tank, smaple of eggs are counted to determine the number of eggs spawned per female. In normal condition, fertilized eggs hatched within 12–15 hours. The hatching rate is measured by assessing the number of hatched nauplii. Nauplii are then transferred directly into the 40-ton tanks if the number of nauplii is between 0.5 million and 1 million. They are then reared directly in the large tank up to the 25th post larval day. On the other hand, if the number of nauplii is less than 0.5 million, they are stocked in 2.5-ton indoor tanks at a density of 100–150 larvae/liter. The larvae are reared either to the third mysis stage (M3) or one day old (P1) post larvae. They are then transferred to the outdoor 40-ton nursery tanks for further nursing.

1. Larval rearing in small indoor tanks

After hatching, the newly hatched nauplii are stocked at a density of 100–150 nauplii per liter in the 2.5-ton larval rearing tanks with fresh filtered seawater filling up to 3/4 of tank capacity. No feed is required at the nauplii stage since the nauplius still utilizes its yolk as food. However, diatom are inoculated immediately after stocking to ensure availability of feed when the nauplii molt into the protozoea stage.

I) Protozoea stage

This is a critical stage of larval rearing. The larvae at this stage start feeding on external food and feed on minute and easily digested microscopic algae such as Skeletonema costatum, Chaetoceros sp. and Tetraselmis sp. The optimal feeding of phytopla ton in the rank is 50,000 cells/ml for Skeletonema or Chaetoceros and 10,000 cells/ml for Tetraselmis.

On the other hand, there is a bright prospect in the use of wet or dry processed invertebrates tissue or encapsulated or microencapsulate feeds in shrimp hatchery feeding strategy. The feeding scheme advocated is based either on the exclusive use of a marine invertebrate wet or dry processed tissue as feed for all the shrimp larval stages or the exclusive use of microencapsulated The use of these types of feed can reduce production cost as well as make the feeding regime of shrimp larvae more convenient especially for small-scale hatcheries. The use of marine invertebrates as food organisms can be purchased at low prices and in large quantities since these are available locally. The commonly used food organisms are paste shrimp (Acetes sp.), rock shrimp (Metapenaeus sp.), stomatopod (Oratosquilla sp.) blood cockle (Anadara sp.) and mussel (Perna sp.)The shrimp larvae are fed with either wet or dried processed crustacean tissue during protozoea stage.

Fig. 6: Schematic diagram of prawn production from hatchery to grow-out ponds.

II) Mysis stage

The larvae at this stage will start feeding on rotifers (Brachionus plicatilis) or the brine shrimp nauplii required depends on the density of shrimp larvae being reared. Each mysis larvae consumes about 100–200 rotifers or about 20–50 Artemia nauplii per day or a standard ratio of about 5 grams dry Artemia cysts is required per cubic meter of rearing water.

2. Larval rearing in large nursing tanks

The initial water level in the 40-ton nursery tanks during stocking is 100 cm. The nauplii density is usually about 20–50 per liter. Immediately after stocking, diatom starters are inoculated to ensure bloom of the desirable species. Technical grade fertilizers can be used directly to enhance algae growth. The fertilizers used are:

KNO3 3 ppm

Na2HPO4 0.3 ppm

It is pertinent to monitor the types and density of algae in big tanks to ensure that the optimal density is maintained.

During the protozoea stage, about 10–20 cm of fresh filtered seawater is then added daily. However, the amount of water added is dependent on the diatom growth. When diatom density is below the desired level in the culture tank, more cultured diatom and fertilizers are added to accelerate algal bloom. On the other hand, over-blooming of algae should also be controlled by shading or by draining out a portion of water and replenished with fresh seawater.

ROUTINE HATCHERY MANAGEMENT

The maintenance of optimal environmental conditions is necessary for maxima growth and survival of the cultured organisms.

1. Maintenance of water quality Salinity - Biologically, most penaeid shrimps do not breed in brackish water while

mating, spawning and even hatching of eggs take place only in the open sea. Salinity in spawning grounds normally ranges from 30 to 36 ppt. Thus, seawater salinity in spawning tanks should be maintained at 30–32 ppt to ensure good hatching rates. Moreover, low salinity affects larval growth during the first 15 days of rearing. Though abrupt or extreme variations in salinity may adversely affect larval survival, slight variations in salinity is not detrimental.

Temperature - Temperature directly affects the metabolic system of any given species. In penaeid shrimps, eggs do not hatch at temperatures lower than 24°C. Larvae usually grow and molt faster at higher temperature. The optimum temperature is 26–31°C. Below this level, larvae do not grow well and molting may be delayed. The protozoea of P. monodon, for instance, molt to mysis stage within 4 days at temperatures ranging from 28°C to 31°C, however, molting takes 6 days when temperature drops to 24–26°C. Slight increase in water temperature above threshold may be lethal in the tropic species. Gradual variations in temperature throughout the day is not critical, however, sudden changes even as narrow as 2°C can cause high mortalities due to stress and temperature stock.

Dissolved oxygen - Dissolved oxygen is a critical factor in larval rearing. High mortalities can occur if aeration stops even for only one hour.

pH and nitrogenous compound - Normal pH of seawater ranges from 7.5 to 8.5. The pH value is a key indicator of changes in the water environment of the rearing tank relative to ionized and un-ionized ammonia. This is so because NH3 and NH4 ratio in water is pH dependent. If pH value is high, this signifies increased levels of un-ionized ammonia (NH3) which is toxic to larvae. Ionized ammonia (NH4 +) however, is not toxic because it is unable to pass through the gill membrane of the larvae. Safe ammonia concentrations in water should not exceed 1.5 ppm for NH4

+ and 0.1 ppm for NH3.

2. Feeds and feeding schemes

Shrimp larvae at the first protozoan stage cannot efficiently seek food as the swimming appendages have yet to develop. On the other hand, diatoms often overbloom in the rearing tank especially those in the outdoor hatchery. This causes high mortality due to attachment of diatom on the appendages of the larvae which makes them unable to move and molt properly. In addition, overblooming of diatom collapses easily the next day and this results in water fouling. To monitor if the feed is sufficient in the rearing tank, the density of diatoms is counted daily before and after water management. Once diatoms in the larval rearing tank become brown, new diatom cultures are added to meet the density requirement of the larvae. The approximate density sufficient for larvae in the rearing tank is 50,000/ml for Chaetoceros sp. or Skeletonema costatum and 10,000/ml for Tetraselmis sp. Brachionus must be maintained at 20 individuals/ml and Artemia at 50 grams for every 100,000 post-larvae. Overblooming of diatoms during summer days is controlled by shading the larval rearing tank or by draining out a portion of the water and replenishing with fresh filtered seawater.

3. Monitoring

Environmental parameters such as water temperature, salinity and pH should be checked twice daily. Meanwhile, the estimated number of larvae at each stage of development should also be recorded. Count larvae in three 1-liter samples for small tanks and 10 times for big tanks. The average number of larvae per liter will give an idea of total amount of larvae. However, larval estimates can be done until P4 only because the larvae changes to demersal feeding habit after this stage. The precise number of larvae will be known during harvest when head counts are done.

NURSERY OF POST LARVAE

Since small tank nurseries normally produce up to P5 - P6 post-larvae only, such stages cannot be stocked directly in grow-out ponds. Therefore, nursing of post-larvae from the small hatchery is still necessary. Nursing of post-larvae can be done in many ways, eg. in concrete tank, earthen pond or in net cages.

1. Concrete tanks

Concrete tanks are prepared by filling up with filtered seawater provided with aeration and pure cultures of diatom added to preserve water in good condition and make it less transparent. Ideal stocking density of the larvae is about 50/cubic meter of water. It is advisable to use substrates to increase surface area in the nursery tank, because postlarvae have a habit of clinging to the wall and tank bottom. Polyethylene nettings can be used and being synthetic, they do not decompose in water and can last longer without deterioration.

2. Earthen pond

Nursery pond size ranges from 500 to 20002 and water depth at 40–70 cm. The nursery pond should have at least one gate installed with a fine screen (1 mm mesh size) to prevent predators and competitors from entering.

Fig. 7: NURSERY POND

P9-P10 are suitable sizes for stocking in the nursery ponds. Stocking density is 100–150 individuals per square meter.

Prior to stocking, the pond should be completely drained and dried until soil cracks. In cases where the pond cannot be completely drained, derris root (Rotinone) may be applied at 20 kg/ha to eradicate predators. Derris root is crushed until it breaks, soaked on water overnight and the resulting milky solution applied. Fertilizers are applied at 1000 kg/ha and 50 kg/ha for organic (chicken manure) and inorganic (Ammonium sulphate) fertilizers, respectively.

Water exchange depends upon the time of spring tide when water can enter the pond. Chopped mussel or cockle meat are fed to the larvae at the rate of 10% the total biomass. The culture period lasts 30–45 days when larvae becomes P40 or P60.

3. Nursery cages

Cages made of synthetic netting can either be floating or stationary in calm water in bays, lagoons or fishponds. Sites for installation of the nursery cages should be as far as possible free from biofouling because nursery cages are made of very small mesh size nettings which can be easily covered up by bio-foulers and thus prevents water exchange. The cages are normally supported by frame and by floating bouys made of bamboo or Styrofoam drums. Stationary cages are held up by bamboo or wooden poles. Postlarvae (P6–7) is suitable for stocking in cages at a stocking density of 1000–2000 per cubic meters of water.

HARVEST AND TRANSPORT OF LARVAE

P21-P25 is suitable for harvesting from nursery tanks because this size can be stocked directly to the pond and easily be transferred. The larvae in nursery tanks can be harvested by first reducing the water level to about 1/3 of its depth and then can be collected from the bag net positioned at the tip of the drained pipe. This method is efficient enough to collect all the larvae.

The postlarvae can also be harvested with a scoop net, dip net or seine net after 2/3 of the tank water has been drained. This method however, is time-consuming.

The number of harvested postlarvae is estimated from a single water basin of known volume from which animals within have been individually counted. This basin serves as a constant where visual comparisons are made with the rest of the harvest in similar basins. This method is reliable especially if the size of the larvae is uniform.

Methods of transporting post-larvae

Tanks – Post-larvae can be transported in plastic, fiberglass or canvass tanks of a suitable transport size (500–1000 liters) and provided with aeration. Temperature of water can be lowered by floating plastic bags with ice. Post-larvae at a density of 200–500/liter can be transported for 10 hours without heavy mortalities.

Plastic bag - Very often, post-larvae are transported in polyethyelene bags provided with oxygen. The bag (60 cm × 40 cm) is first filled with 6–8 liters of fresh seawater and then packed with 3000–5000 post-larvae. The density may be reduced if the expected transport time is longer. After properly tightening the mouths of the bags, they are placed in styrofoam boxes or plastic buckets. Temperature is reduced to about 22–25°C by crushed ice mixed with sawdust on the bottom, side and top of the styrofoam box. Under these conditions, post-larvae may be kept alive for more than 12 hours during transport.

GUIDELINES — SHRIMP HATCHERIES

Community property rights and regulatory compliance Community-community relations

Fig. 8: Nursery Cages (stationary cages & floating cages)

Community-worker safety and employee relations Environment-ecosystem protection Environment-effluent management Food safety, drug and chemical management Environment storage and disposal of hatchery supplies

CONCLUSION

Shrimp hatcheries may require some facilities, such as pipe -lines, to be located on public land. Where this is the case, hatcheries shall ensure that local communities are consulted, approval is granted by pertinent authorities and adequate precautions are taken to prevent the facilities from being a hazard, nuisance or eyesore. In residential areas and especially at night, special care shall be given to minimize noise pollution, such as that caused by electric blowers, generators or other intensive activities. Shrimp hatchery management should attempt to accommodate traditional uses of coastal resources through a cooperative attitude toward established local interests and environmental stewardship. Hatcheries should not block traditional access corridors to public mangrove areas and fishing grounds.

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United Nations (FAO) Glossary of Aquaculture.2. FAO (2010) State of World Fisheries and Aquaculture.

3. Frankenberger (2002). A livelihood analysis of shrimp fry collectors in Bangladesh: future prospects in relation to wild fry collection. Report from the Shrimp Action Plan. Department of Fisheries/DFID.

4. Huntington (2002). Scoping study for the certification of shrimp aquaculture in Bangladesh. Report from the Shrimp Action Plan. Department of Fisheries/DFID.

5. BOBP (1993) Nursery rearing of tiger shrimp post larvae in West Bengal, India. BOBP/WP/92.

6. BOBP (1994) Cage nursery rearing of shrimp and prawn fry in Bangladesh. BOBP/WP/92.

7. Banks (2002). Brackish and marine water aquaculture. Report from the Fisheries Sector Review. DFID.

8. Chanratchakool, P. 1993. Health Management in Shrimp Ponds. Aquatic Animal Health Research Institute, Bangkok, Thailand. 111 pp.

9. FAO. 2007. Improving Penaeus monodon hatchery practices. Manual based on experience in India. FAO Fisheries Technical Papers T446. Rome, FAO. Online version.

10. Kongkeo, H. 1997. Comparison of intensive shrimp farming systems in Indonesia, Philippines, Taiwan and Thailand. Aquaculture Research, 28:789-796.

11. Kungvankij, P. 1986. Shrimp hatchery design, operation and management. NACA Training Manual Series No.1. NACA, Bangkok, Thailand. 88 pp.

12. Limsuwan, C. & Chanratchakool, P. 2004. Shrimp farming industry in Thailand. National Research Council of Thailand, Bangkok, Thailand. 206 pp.

13. Rosenberry, B. 1996. World Shrimp Farming 1996. Shrimp News International, San Diego, USA. 164 pp.