PART II
L E C T U R E S

BRIEF NOTES ON THE GIANT FRESHWATER PRAWNS AS AN OBJECT OF FARMING

by

V. Soesanto¹

1. INTRODUCTION

In the tropical countries of Asia and the Far East, the long legged giant prawn (Macrobrachium rosenbergii) has been known as food item for the people since long years ago. The prawn can attain big size which makes its capture wherever it occurs become an item for commercial venture.

In the region where Macrobrachium fisheries has existed for centuries and in certain other countries, there is an intensive exploitation on a considerable scale, some of these are big enough to support export. Macrobrachium rosenbergii is one of the freshwater species possessing high potential and good market demand.

In line with the growing market demand, during the last decade the exploitation of the species has become more and more intensive. Fishing of this prawn is usually by the use of traps, cast net, or gill net.

In general at present, there is significant decline of catch from natural stocks almost everywhere in countries in the region. Harvest has diminished owing to indiscriminate fishing which cause the stock decrease soon. The reduction of stock is also due to the destruction of habitat by human being. Construction of dams, roads and factories in the lower reaches of the river systems leads to the reduction of the dispersal area of the prawns including the spawning and feeding grounds. Water pollution is another factor which is positively deplete on the growth and abundance of the stocks.

In early sixties (1962), Ling in Malaysia has managed to raise the species through complete metamorphosis. He succeeded in rearing larvae to juveniles and from juveniles to young and adults. The larval stage require brackishwater for survival and under natural conditions the juveniles migrate to freshwater.

Experiments show that Macrobrachium can be successfully cultivated in ponds. Knowledge in the field of techniques and culturing methods has remarkably improved and at present the prawn has become the subject of intensive efforts to cultivate.

¹ Fisheries Training/Extension Officer, FAO/UNDP South China Sea Fisheries Development and Coordinating Programme, Manila, Philippines.

2. DISTRIBUTION

The giant prawn Macrobrachium rosenbergii is widely distributed in the tropical and subtropical countries of the Indo-Pacific Region; including Bangladesh, Burma, Cambodia, India, Indonesia, Malaysia, Pakistan, Philippines, Sri Lanka, Thailand, and Vietnam. In most of the countries especially in South and Southeast Asia, it occurs in quantities inhabiting rivers, streams, lakes, swamps and even reservoirs, which have connection with the sea. In the wild, the prawn occurs the whole year round inhabiting freshwater, and rather often in brackishwaters with the main concentrations, respectively in lowland areas in the lower reaches of the rivers which are influenced by tides. It is also known to occur in waters far away from the coast. The prawn could migrate more than 200 km upstream entering lakes, water reservoirs, irrigation canals and even paddy fields. This migratory ability does not only apply to M. rosenbergii, but there are some other species within the Genus Macrobrachium which are also capable of such dispersion. Therefore, in countries where more than one species are present, the possibility of mixed species is great.

Table 1 shows the occurrence of some species which can grow in both fresh and brackishwater (ANNEX I).

3. TAXONOMY

The classification of Macrobrachium rosenbergii is as follows:

Within the genus Macrobrachium, there are 49 species described by Holthuis (1980) in his Catalogue of species, from which 27 species occur in Asia and the Pacific region. Most of the species are inhabitants of freshwater, but a few inhabit freshwater, brackish or some times even saltwater area.

The size they attain varies by species from less than 10 cm to much bigger size over 20/30 cm. Macrobrachium rosenbergii can reach a maximum total length of 320 mm for male specimen and 250 mm for females.

For identification of the species, Holthuis (1950) described the following characters:

• Carpus distinctly longer than the merus

• Rostrum with a distinct elevated basal crest generally very long, or with a distinct naked portion in the distal of upper margin

• Lower margin of rostrum with 8–13 teeth

• Rostrum long and curved upwards

• Tip of telson reaching beyond the tip of the longer posterior spines.

4. BIOLOGY

The freshwater giant prawn Macrobrachium rosenbergii is the most hardy and resistant species within the genera of Macrobrachium. It can easily tolerate different salinities of water from fresh- to saltwater, therefore, this species is considered euryhaline. The animal is known for its rapid growth, with the males growing faster compared to the females.

The adults are omnivorous, eat greedily and frequently on both plant and animal materials. Pieces of worms molluscs, crustaceans, cut up flesh and internal organs of fish and other animals, grains of rice, wheat, peas, beans, ground nuts, coconuts, fruits, pellets of poultry feed, etc. are items that are readily consumed. Tender stems and leaves of aquatic plants, such as Ipomoea reptans are also eaten when no other better food is available. When sufficiently hungry, it may even become cannibalistic.

Food materials are located mainly by the sense of smell and touch. When searching for food the first and second pair of the thoracic legs which are chelate sweep about actively.

The prawn is usually quiet during day time and stays at the bottom of waters without much active locomotion and tends to avoid strong illumination. They are active at night time, searching for food.

When mature, male prawns are considerably larger than females. The second thoracic legs are extremely long and rather thick, the head is big, the abdomen compact with very little space between the pleura, and the genital pores are at the base of the fifth thoracic legs. Females are generally smaller than the males, the second thoracic legs are shorter and more slender and the head is smaller. There is a spacious brood chamber below the abdomen, formed by the downward prolongation of abdominal pleura, and genital pores are at the bases of the third thoracic legs.

The ripe ovaries can be seen through the carapace as large orange coloured masses occupying a large portion of the dorsal and lateral parts of the cephalothorax. Sexually mature males are able to mate at any time, while the females are ready to respond only after completing their premating moult.

The moulting that takes place shortly before mating or spawning is called premating or prespawning moult, to differentiate from the ordinary moulting. The frequency of moulting depends on the age, availability of food, quality of food, and also is affected by the water quality. Young specimens moult more frequent than old ones. Animals obtaining enough and good quality of food moult sooner than those taking less or poorer food. Females with actively developing gonads getting ready for spawning, take longer period to moult. Ordinarily the interval between two moults is 20–40 days. Newly moulted specimens are weak and vulnerable to predation. It takes 2–6 hours for the new shell to become sufficiently hardened.

A large number of species of Macrobrachium which includes M. rosenbergii is known that they reach sexual maturity long before attaining their maximum size. Under tropical conditions, mating occurs throughout the year within 6–20 hours after mating the eggs are laid; and unmated ripe females may lay eggs within 24 hours but the eggs are not fertilized and drop off in two or three days. The laying of one whole batch of eggs is usually completed within 20 minutes where the eggs are extruded through the female genital pores into the brood chambers. Fertilized eggs will hatch in approximately 18–21 days during incubation period. The number of eggs produced by each individual female depends upon the size of the specimen. Some workers estimated the number of eggs varies from 800–1000 per 1 gram of body weight. But practices show it is easier to estimate the number of newly hatched larvae rather than the number of eggs.

* = After Adisukresno et al. (1977)

From the time of hatching to the juvenile stage, the development of larvae takes 30–45 days through a series of metamorphosis (stages), all larval stages require brackishwater to grow which corresponds to at least 5 ‰ seawater. Specimens which live in pure freshwater and fail to reach brackishwater within 4–5 days would not be able to survive.

They are planktonic in habit and are active swimmers whereas during the early stages, they tend to move around close together in large groups, usually close to the surface of the water. This milling together disappears in about 10 days. Their swimming position is peculiar, tail first, ventral side up with the head lower than the tail.

The larvae are attracted by light, but direct sunlight and other strong lights are avoided, and through the whole larval stages they eat continuously as long as food is available in the form of living food and suspended particles of suitable sizes.

As soon as the larvae metamorphose from the last larval stage, they cease to be planktonic or pelagic. They settle to the bottom as crawlers or attach themselves to vegetation and submerged objects as juveniles. Under natural conditions, these newly transformed juveniles still remain in brackishwater for several weeks before starting the migration upstream towards freshwater for their wide dispersion. They feed on tiny worms, small crustaceans, insect larvae and a variety of organic materials. In good environmental conditions, they can attain about 5 cm in two months and can survive wide temperature ranges.

5. FARMING PROSPECT

The freshwater giant prawn has been known as quick growing and is a superior animal for culture. Experimentations to grow Macrobrachium rosenbergii have been tried by several workers since before 1960.

Workers in Thailand started growing prawn in earthen ponds in 1956 with juveniles collected from the open waters. From the experiments, it shows that Macrobrachium could well be used for pond culture. Young prawns are able to survive well in varied types of freshwater, provided that the water contains enough amount of dissolved oxygen. Since the success of Ling (1969) in rearing larvae to juveniles and from juveniles to grown adults of marketable size, growing prawn in ponds has evolved. The giant freshwater prawn can even be cultivated in irrigated padi-fields that are able to retain water depth not less than 15 cm. At present, information available does not identify any other species with greater potential than Macrobrachium rosenbergii.

The culture technique of growing prawn is relatively simple due to the resistance of the animal to changes of environmental conditions such as temperature and salinity and it is omnivorous in nature. Production cost is low and the product is highly valued in the market. The demand of prawn is getting progressively greater, hence efforts for increased production are necessary.

The freshwater giant prawn has now become a subject of efforts to cultivation.

6. REFERENCES

Adisukresno, S. and A. Purnomo. 1977 Mass production of Macrobrachium rosenbergii fry in Indonesia: Problems and prospects. ASEAN Meeting of Experts on Aquaculture, Semarang, Indonesia, 31 October 1976 to 6 February 1977

Holthuis, L.B. 1950 The palaemonidae collected by the Siboga and Snellius Expeditions with remarks on other species. I. Subfamily Palaemonidae. The Decapoda of the Siboga Expedition, Part X. Siboga Exped. Monogr.

Holthuis, B. 1980 FAO species catalogue. Vol. 1. Shrimps and prawns of the world. An annotated catalogue of species of interest to fisheries. FAO Fish Synop., (125), Vol. 1: 261p.

Ling, S.W. 1969 The general biology and development of Macrobrachium rosenbergii (de Man). FAO Fish. Rept. 3(57): 589–606

Waterman, T.H. 1960 The physiology of crustacea. Vol. 1. Metabolism and Growth. Academic Press, New York

ANNEX I

Macrobrachium species in different countries that occur in both fresh- and brackishwaters

LIFE HISTORY OF MACROBRACHIUM ROSENBERGII DE MAN

by

Gregorio L. Escritor¹

1. GENERAL DISTRIBUTION

During the last decade, the giant freshwater prawn, Macrobrachium rosenbergii has emerged as the most talked/discussed species in the family of freshwater prawns. The breakthrough in the artificial breeding of the species done by Dr. S.W. Ling, then an FAO Regional Fish Culturist in Asia and the Far East in 1961, has attracted a number of biologists. Many indepth studies have been done and are still being undertaken in respect to the growth rate, ecology, mode of breeding (migration movement), feed and feeding habits, genetics, etc. aim towards commercial production of post larvae in hatchery and marketable prawn from the growout ponds.

The species is widely distributed in the tropical and subtropical countries. It is more abundantly observed in the Indo-Pacific Region in the estuarine areas specially in the entrance of rivers, streams and creeks directly emptying into the sea. They are commercially caught in the upper reaches of freshwater rivers and inland lakes. It is highly a euryhaline species that can tolerate or exist in both freshwater and brackishwater with a wide-range of salinity. They are being caught also in man-made lakes, irrigation canals, and dams, including some paddy fields.

2. FOOD AND FEEDING HABIT

The giant prawn is an omnivore and feed greedily. In nature, they feed upon young molluscs, crustaceans, worms, flesh of both aquatic and terrestial animals, grains, nuts, beans, coconut meat, pieces of some fruits, etc. Actually they are also cannibalistic since they devour their own kind when they encounter soft shelled individual except perhaps when they are in a premating moulting when the female is guarded by the male.

They continue to crawl on the bottom in search for food or cling on submerged vegetation including those along embankments of rivers or lakes or impoundment or among hanging roots of floating aquatic plants such as the water hyacinth. They can be observed also nibbling epiphytes among submerged twigs and branches.

¹ Project Manager, FAO/UNDP Brackishwater Aquaculture Development Project (BADC), Jepara, Central Java, Indonesia

3. CHARACTERISTICS OF ADULTS

3.1 Male

Among adults the male prawn is much bigger than the female. It is differentiated by a pair of long and rather thick second thoracic legs which is the pincer. It has a very prominent head and compact abdomen with very little space between its pleura. A genital pore is present at the base of its fifth thoracic legs.

3.2 Female

A female is comparatively smaller than a male with shorter and slender second thoracic legs, a medium head and a spacious brood chamber. The genital pores are located at the base of its third thoracic legs.

When the female is sexually ripe the fully developed ovaries can be seen through the carapace. It is a large orange mass occupying a large portion of the dorsal and lateral parts of the cephalothorax.

The swimmerets become slightly distended and arched outward to form a large “brood chamber” to accommodate the enormous number of eggs to be laid.

The basal segments of the pleopods, particularly those of the first three pairs are elongated and are equipped with much branched setae on their inner margins which are developed during spawning to accommodate the eggs which are attached in bundles to this setae through an adhesive substance as the eggs are extruded.

4. MOULTING

Generally among arthropods, the body is usually covered with hard chitinous coating known as the exoskeleton. This hardened integument is a good protection of the body of the animal. However, like other crustaceans it prevents the expansion of the body. Hence, the shedding of the exoskeleton or moulting becomes a necessity in order to institute growth. As a natural process when the animal have accumulated enough body tissues, body expansion becomes inevitable. At this process, a new thin, soft and elastic sheet is developed gradually but steadily immediately underneath the old hard exoskeleton. When the new coating is fully developed, the animal becomes quiet and try to separate and seclude itself from the others to shed off the old hard shell. As soon as the old shell is shedded, the new shell which is soft and elastic expand due to pressure emanating from the accumulated mass of body tissue. This body expansion is actually the unit of growth which periodically have to take place in the animal in the process of growing. Just after the old shell is shaken off, the animal is very soft. It takes hours before it is hard enough for the prawn to resume its normal active life. During the time that the shell is soft, the animal is immobile and helpless when attacked by predators. This is probably the reason why the animal seclude itself during moulting.

The casting off the old shell is rapidly accomplished in a matter of minutes. The prawn try to bend its body to exert strong internal pressure until a dorsal transverse split occur in the membranous part between the cephalothorax and the abdomen. Then the animal bend its abdomen ventrally forming an inverted “U” shape arc dorsally, until a portion of the body is out through the split dorsal opening. As the abdomen gets rid of its cast, it bends anteriorly to facilitate the release of the exuvium of the cephalothorax. In the process, it is possible that a longitudinal split along the sides of some segments of the large thoracic appendages also occur to ease the withdrawal of the new limbs.

The frequency of moulting depends largely on the quality and quantity of food taken. And like any other organism, growth rate is faster at younger stages and gradually slows down as the animal gets older. Hence, moulting is more frequent when the prawns are young.

5. BREEDING BEHAVIOUR

Mature male prawns are always ready for copulation. They can perform intercourse whenever the female is ready. On the other hand, the female have to be in a certain stage/condition in order to be able to mate.

6. PREMATING MOULTING

Mating cannot be performed if the exoskeleton of the female is hard. Therefore, to consumate the act the female have to undergo a premating moulting. It will take only a few hours before the new shell hardens, hence, it is necessary that mating should take place at certain precise state of the shell. It should not be too soft nor too hard. When it is too soft, the male is liable to devour the female. If the shell becomes fully hardened, mating may not be effectively performed or no mating occurs.

In other words, the female has to prepare itself for a “love” affair everytime she is ready to spawn in order to fertilize the eggs and young ones be borned.

7. COURTSHIP

How does the male know that the female is undergoing a premating moulting as differentiated from ordinary growth moulting?

Dr. Ling, in his study, theorized that in the premating moulting, the female releases certain kind of substance to attract the male. When the male notices this, then it immediately starts courting the female instead of devouring it. It will display its masculine grace and strength by lifting its head, raising its body, waving its feelers and raising and extending its long and powerful thoracic legs in an embracing manner with intermittent jerking movements until the females favour is won.

8. MATING

Upon agreement the male holds the female between its pair of long thoracic legs at the same time cleaning the ventral portion of her shells in the thoracic region with its other legs. This is followed immediately by the actual copulation which takes only a few seconds like a lightning. The sperm is deposited in one mass on the ventral thoracic region between her thoracic legs. The sperm is coated with thin layer of gelatinous substance for protection and to keep them intact.

9. EGG-LAYING (SPAWNING)

Whether the female is mated or not, it will lay eggs in about 24 hours following the premating moulting. During the ejaculation of the eggs, the mother prawn bends its abdomen forward as far as it could reach to touch the ventral thoracic region. The eggs which are extruded through the genital pores are directed into the “brood chamber”. They are held together by some extremely thin and membranous substance and are deposited first on one side, starting on the chamber between the fourth pair of pleopods and so on to the third, second, and finally to the first. The eggs are held in bundle tightly to the fine ovigarous setae of the first four pairs of pleopods.

10. INCUBATION AND EMBRYONIC DEVELOPMENT

The eggs, like bunches of berries in the brood chamber are carried by the brood during the whole incubation period which lasts approximately 18–21 days, depending on temperature. During the incubation period, the mother prawn moves the pleopods back and forth intermittently to provide sufficient aeration to the eggs. In the meantime, the first pair of the thoracic legs is busy cleaning the eggs of any foreign matter.

Embryonic development immediately starts as soon as the eggs are extruded. The first nuclear division will be observed about 4 hours after fertilization. The cleavage is completed in about 24 hours. Rudiments of the body region of the embryo will be visible on the third day and appendages will be formed on the fourth day. The eye pigment starts appearing at the end of the eight day. The heart is formed and start beating on the tenth day. The embryo is actually formed on the twelfth day which is subsequently followed by the larvae development on the seventeenth day. Midway of the embryonic development period, the egg orange pigmentation turns light gray to dark gray as the embryo is further developed until it hatches.

11. THE HATCHING PROCESS

The breaking of the eggs is accomplished by a slow but continuous vibration of the mouthparts of the larvae, coupled with the stretching of the rolled up body forcing the eggs to elongate gradually. As these mouthparts vibration and body stretching increase its force, these are reinforced by the intermittent vigorous vibration of the thoracic appendages for about 10 minutes with increasing intensity. This continuing and increasing force is soon accompanied by the stretching of the telson outward until the egg shell breaks up and the telson thrushes out first followed by the head and with strong body bending and stretching the larva springs out of the egg case.

12. THE LARVAE

The newly hatched larvae which are devoid of many segments and appendages of the adult start swimming in about 5 minutes after coming out of the egg shell. At this point in time, the water must be brackish. The minute and fragile larvae have no semblance to their parents. While they are attracted by light, they avoid strong illumination and direct sunlight. During the entire larval stages, they remain pelagic and actively swim around upside down grasping their food as they come across. They are voracious feeder and will eat continuously as long as food is available.

The food consists of zooplankton such as copepods, minute protozoans, rotifers, cyclops and pieces of animal flesh, food grains, fruits, etc. The food is grasp by their thoracic legs as they swim.

13. LARVAL STAGES

According to the study of Dr. Ling, there are about 13 larval stages. These development stages from hatching up to final metamorphosis is completed in about 45 days. Obviously growth rate is influenced by water temperature and quality of food. You may observe that fast growing individual larvae may complete metamorphosis in less than 25 days.

¹ See attached Figures 1 to 12.

14. JUVENILE

As soon as the larvae metemorphose, they lose their pelagic characteristics and become bottom crawlers or cling to submerged objects such as leaves, roots, stems and branches of aquatic and semi-aquatic vegetation. This time they feed greedily on aquatic worms, bottom insects and larvae, fish eggs, tiny fry or other aquatic animals, algae, and particles of organic materials including some epiphytes.

The larval transformation to post larval stage marks also the end of their life in brackishwater. From this stage on, they start their positive rheotrophic migration. They swim against swift currents by tightly crawling on the bottom. They can migrate up to inland lakes and dams passing along sides/edges/embankments of streams. During flood seasons, they further move upward to ricefields, small lagoons and freshwater ponds which are not accessible during dry season. From the beginning of their upstream migration up to their adulthood, the prawns stay in the freshwater as their permanent abode.

15. SEXUAL MATURITY

Dr. Ling in his study stated that the female prawn attained its first sexual maturity on the tenth month when they are about 12 cm or more in length. Our observations in some ponds in Central Java indicated that some prawns attain their first sexual maturity in less than six months. Sampling of prawns from the pond stocked with fry after six months showed many berried females.

A sexually matured female will develop the gonads and will lay eggs whether it is mated or not. However, the eggs of unmated female will fall off in a few days as such eggs would not hatch. Some females were observed to spawn twice in four months under controlled condition. The number of spawning per female per year in the natural habitat is yet to be further observed.

It can be assumed under natural conditions that as the female develops its gonad it starts its negative rheotrophic migration. Somewhere along the way, it undergoes premating moulting and gets mated. At this point, it should reach tidal lagoons or mouths of tidal rivers where water remain brackish all the time for the hatching of the eggs and subsequent development of the larvae. If the mother prawn fails to reach the brackishwater area in this journey the young larvae will die within three to four days after hatching.

16. REPRODUCTIVE CAPACITY

Some studies on the fecundity of the giant prawn showed that they have quite high reproductive capacity. A female of about 17.2 cm long weighing about 65 g can produce about 90 000 eggs. Large females are assumed to be able to produce a lot more. Fujimura, preliminary established a weight/number relationship in estimating the fecundity of female prawn. The total number of eggs is estimated by multiplying the total weight of the spawner in grams by 750.

17. MIGRATION

Movement of the prawn chiefly migration, like any other aquatic fauna is influenced by many factors mainly physical, chemical and biological stimuli. While the positive and negative rheotrophic migration of the prawn to complete its life cycle may be a natural instinct, it is quite obvious that it may be associated with chemical stimulus. The desire to hatch and grow the young larvae in a brackishwater to perpetuate its kind requires the prawn to perform the journey. Perhaps temperature also play an important roll since the water is warmer in the coastal areas than upstreams.

18. REFERENCES

Ling, S.W. and A.B.O. Merican. 1961 Notes on the life and habits of the adults and larval stages of Macrobrachium rosenbergii (De Man). Proc. Indo-Pacif. Fish. Coun., 9(2): 55–60

Ling, S.W. 1960 A general account on the biology of the giant freshwater prawn, Macrobrachium rosenbergii and methods for its rearing and culturing. FAO/UN Mimeo. Paper presented to the Indo-Pacific Fisheries Council, 11th Session, 16–31 October 1964

Ling, S.W. 1962 Studies on the rearing of larvae and juveniles and culturing of adult of Macrobrachium rosenbergii (De Man). Curr. Aff. Bull. Indo-Pacif. Fish. Coun., 35: 1–11

SITE SELECTION FOR FRESHWATER PRAWN HATCHERY

by

Haniah Suharto¹

1. INTRODUCTION

Freshwater hatchery can be built far or near the coast. This depends on the technology to be used. It is feasible to construct the hatchery far from the sea, if we apply the recycling system of rearing the larvae in the conical fibreglass tank without green water as larval medium. An ideal giant prawn hatchery has to consist of hatchery, nursery and spawner ponds, and all these components situated at one location. In finding a good site or which we will build a hatchery, its characteristic has to be determined.

We will discuss a development of a hatchery near the coast. As it is well known, the condition in individual locations are variable, hence the necessity for detailed studies for each prospective area to be chosen should be emphasized. It thus follow that the suitability of the location chosen for construction of a hatchery will have to be determined beforehand.

2. SURVEY OF PREFERABLE SITE

According to facilities available, two types of surveys may be undertaken, reconnaissance and detailed survey. Both types of surveys may be taken up simultaneously.

The survey team should include, at least biologist or aquaculturist and the necessary supporting staff.

3. FACTORS TO BE STUDIED

The main factors to be taken into consideration for the survey are:

1. Type of area
2. Land regulations and rights
3. Tidal fluctuations
4. Soil characteristics
5. Water characteristics

6. Accessibility and market for sale of juveniles

¹ Research Staff, Inland Fisheries Research Institute, Bogor, Indonesia

3.1 Type of area

This is whether the site is swampy, marshy, mangrove swamp, etc., with appreciated area as available. The coast should be stable, no erosion and siltation. The bottom has to consist of sand, gravel or reef.

3.2 Land regulations and rights

Information on these aspects have to be gathered from the concerned authorities. Any possible legal hurdles in acquisition of land should be taken care of.

3.3 Tidal fluctuations

Tide tables for the nearest reference place or port should be obtained before the survey is undertaken. This table will give the approximate predicted time and height of high and low waters at the site for each day of the year.

Land elevation and tidal fluctuations are important factors in determining the suitability of the area for the construction of hatchery.

The tidal flooding values of the site will have to be related to tidal fluctuation. The location of where the well will be constructed as depository of seawater of the hatchery should also be investigated.

3.4 Soil characteristics

Information on the soil type and its characteristic have to be gathered from the concerned institute. It is important for the hatchery if there is any possibility to construct the ponds.

3.5 Water characteristics

There are two types of freshwater sources, well and natural waters (river or swamp). Collection of water samples is necessary using water samplers, such as Kemmerer's, Frisdinger's or Nansen's.

Data have to be collected and recorded properly.

3.5.1 Well as freshwater source

3.5.1.1 Depth. The depth of the well is determined by using the cord and recorded in cm.

3.5.1.2 Turbidity. Several methods are used to measure the turbidity, such as the secchi disc method, U.S. Geological method, Jackson candle turbidimeter method, and Hellige method. The first method is the simplest one.

3.5.1.3 pH. The most commonly adopted method under field condition for the determination of pH, are by using “Lovibond” comparator and standard BDH test paper. The other method, which will give more precise result is by the use of electrode.

3.5.1.4 Salinity. In field condition, salinity can be estimated by titration or using the refractometer. The titration gives the estimation of the chlorinity, which can be used to calculate salinity as indicated by the formula:

S = 0.03 + 1.805 cl

The refractometer can determine directly the salinity in part per thousand (ppt).

3.5.1.5 Pollution. The pollution may be of agricultural discharge such as pesticide or fertilizer residue.

3.5.1.6 Distance. If the well is out of the area surveyed, the distance has to be estimated with the location.

3.5.2 River

This freshwater source is needed for watering the pond where the female stocks are reared. The data are collected and recorded as it is done in determining the quality of the freshwater from the well. In addition, the debit of the flow has to be estimated.

3.6 Seawater source

This source is important to the larval media, since the media has to have a certain salinity from 10–15 ppt. Water characteristic determination are as follows:

• turbidity
• salinity
• depth

• temperature

There are two types of saline water source, river and the sea. The river water source can vary greatly since the river has tidal fluctuation which have to be related to the tidal flooding. For this reason, it is advisable to avoid using this source of water as media for larval rearing, if possible.

Seawater with minimum seasonal fluctuation on quality is most desirable. It should not be affected by inland discharge containing agricultural runoff or industrial wastes. Adequate volume of seawater should be available anytime when needed and the salinity should be stable (28–31 ppt).

Seawater can be obtained directly from the sea or pumped from the well which is built near the coast and out of the high tidal levels.

6.7 Accessibility and market for sale of juvenile

Information regarding the road to the site under survey can be collected from various sources and also by on-the-spot studies.

Information regarding marketing facilities for instance the surrounding pond area which can be used as rearing pond to absorb the juvenile production.

Data that should be collected concerning this subject are:

• distance to the main road
• distance to town
• distance to the public service facilities
• electricity

• the freshwater pond area

4. EVALUATION

Data collected of some sites surveyed have to be evaluated to choose the preferable one. The evaluation will be made by comparison among the different parameters qualitatively and quantitatively.

HATCHERY DESIGN

by

Sukotjo Adisukresno¹

1. INTRODUCTION

The success of a Macrobrachium hatchery depends on several factors:

1. The suitability site for hatchery
2. The quality and quantity of the personnel
3. The hatchery design and layout which determines the efficiency of operation and economic aspects

4. Adequate equipment and supplies

In this course, only hatchery design will be discussed. The design of a hatchery should be:

1. Low cost and fast in construction
2. Efficient on the operation
3. Applicable to the environment

4. Technically durable

Layout of the hatchery components should be arranged according to the:

1. Topography of the site
2. Efficiency on the operation
3. Possibility of expansion

4. Should restrict public interference

¹ Director, Brackishwater Aquaculture Development Centre and concurrently Co-Manager, FAO/UNDP Aquaculture Development Project, Jepara, Indonesia.

Fig. 1. Layout

Remarks

1. Residence quarter (if needed)
2. Office and laboratory
3. Saltwater tank (tower), space underneath might be used for pump and blower storage
4. Greenwater tanks (tower), space underneath might be used for storage of hatchery equipment
5. Freshwater tower and deep well
6. Power house

7. Greenhouse with hatchery tanks

2. CONSTRUCTION

Tanks should be constructed so that they are strong enough and durable. This concerns water engineering. Any small leakage or crack may cause serious damage to the construction.

2.1 Saltwater and greenwater tanks (tower)

The saltwater and greenwater tanks are in tower, so that water flows into the hatchery tanks by gravity. The greenwater tanks tower is lower than the saltwater tank so that saltwater flows into the greenwater tank by gravity. The construction of the tower is of reinforced concrete so that the tower and tanks can be strong enough, especially when the tank volume is big (over 10 m³).

The space underneath the tower might be used as room for water pump and blower and also for storage of hatchery equipment. The saltwater tank is provided with sand filter, so that water flowing from this tank is clean enough to fill in greenwater tank or hatchery tanks.

2.2 Freshwater tower

This tank might be of concrete or fibreglass tank. The height should be higher than the greenwater tanks. Freshwater might come from open well or deep well. Water from the drinking pipe supply should have its chlorine content removed by aerating the water for 1–2 days before use for the hatchery.

2.3 Greenhouse

In tropical countries, where the rain is heavy, greenhouse is necessary to cover the hatchery tanks. Dilution of saltwater in the hatchery tanks by rainwater cause heavy mortality to the larvae. Greenhouse roof might be of glass, plexy glass or corrugated plastic roofing. Since Macrobrachium larvae avoid strong light and can tolerate the temperature up to 30°C only, the light intensity in the greenhouse should be reduced by painting the glass roofing or set dark shelter in the greenhouse. The ventilation in the greenhouse should be provided to prevent increase in inside temperature (Fig. 1).

2.4 Hatchery tanks

These tanks might be made of concrete, fibreglass, plastic pools or wooden box with plastic lining.

2.4.1 Concrete tank

Tanks made of concrete might be square, rectangular or circular. They can be constructed of all concrete or partial concrete. Square and rectangular tanks should be rounded at their corners, because perpendicular (90° corner) corners are difficult to clean and are the place where the debris accumulates.

Newly constructed tanks are dangerous to the larvae, because they are highly alkaline due to the cement which dissolved into the water. To avoid this, the inner wall should be painted with epoxy paint. Volume of tanks varies depending on requirements; they vary from 3–15 tons (Fig. 1).

2.4.2 Fibreglass tank

This tank might be square, rectangular, circular or conical type. It is durable and can be constructed quickly. But in the developing countries, the price is expensive. Bigger tank need support to prevent the tank swollen. The conical type need special support, it mean addition of investment. The volume varies from fifty 1–15 tons.

2.4.3 Plastic pool

This pool is transferable from one place to another. Before the pool is set, level the ground and clean from other sharp object. It consists of the outer frame made of aluminum pipe and aluminum frame, and the inside layer made of rubber and plastic material reinforced with strong textile material. The price is comparatively cheap, but only a few countries in the world produce these pools.

2.4.4 Wooden box with plastic lining

It is cheap, the materials to use are available everywhere and the construction is fast.

Materials required:

• 12 pieces of wooden planks of 4 m length, 20 m wide and 3 cm thickness

• 4 wooden pieces of 4 m × 8 cm × 8 cm for frame

• plastic lining of about 24 cu. m

Clean and level the ground where the wooden tank is going to be placed. Set the wooden frame and stake the post of 1.0 m outside the frame. Set the plastic lining. The plastic sheets are usually sold in rolls of 1.5–2 m wide, it is needed to glue the plastic sheets with each other until you get the desired width (Fig. 1).

Fig. 2. Green house, side view

Fig. 3. Green house, front view

Fig. 2. Wooden tank with plastic lining

HATCHERY OPERATION

by

Sukotjo Adisukresno and Kisto Mintardjo¹

1. ELEMENTS

Hatchery operations concern the practical knowledge of handling and transportation of berried females, care during incubation period, hatchery management, post larval care, and fry transportation.

1.1 Berried females handling and transportation

Berried females might be collected from streams, rivers, lakes or swamps or from farm ponds. To collect berried females, traps, cast nets or scoop nets might be used. The animals should be handled carefully in such a way to prevent them from struggling and jumping, as this will cause many eggs to drop off and reduce the number of larvae produced.

For transportation from the pond to the hatchery, large barrels of 60 liters capacity provided with aeration from a battery-operated aerator can be used. Since all the prawns tend to stay at the bottom, many eggs might drop off. To overcome this disadvantage, only 4–6 berried females should be transported with this method. In this case, when a large number of animals are transported, many barrels and adequate space will be required. A method which is the most advantageous so far is the use of large conical barrels provided with 4–5 shelves made of framed netting materials. On each shelf, 8–10 specimens are kept, so that 32–50 berried females can be carried out in each barrel (Fig. 1). When transfering females from the barrels, each shelf is taken out slowly, the prawns rest quietly on each shell so that there is no lose of eggs. The animals might be transported within 8–10 hours by land with no mortality with this method.

1.2 Care during incubation period

During incubation which takes 1–18 days (depending on the maturity stage of the eggs), the spawners are placed in containers, for example aquaria, small tanks, etc. During this period, the animals are fed with food which does not integrate in the water, otherwise it will lower the water quality. The food may consist of sweet potato, cassava, Colocasia, etc. It is necessary for the animals to have the maturity of their eggs accelerated. The water salinity should be maintained at 8–10 ppt.

¹ Chief, Shrimp Culture Section, Brackishwater Aquaculture Development Centre, Jepara, Indonesia

When the larvae appear, the aeration is stopped to allow the larvae to swarm on the water surface. They are siphoned out into a bucket of certain volume.

Make the water volume say about 10 liters. Give strong aeration into this bucket so the larvae will distribute evenly. Take several samples with a known volume sampler, say 100 ml. Count the number of larvae in each sample and compute the average number for the samples. With this method the number of larvae can be estimated.

Example:

Volume of water - 10 liters
Volume of sampler - 100 ml
Number of larvae per sample:

The larvae are then transferred into the hatchery tanks. The method practiced in Hawaii is slightly different. On the top of the hatchery tank is placed the incubation tanks of fibreglass. When the larvae appear, they are poured directly from the incubation tanks into the hatchery tanks.

1.3 Hatchery tanks operation

Before filling with water, the tanks should be thoroughly washed so that no benthic algae are left. The tanks are allowed to dry under the sun for one day. Then they are filled with clean brackishwater of 12 ppt up to 3/4 of the volume of the tank, and add green water which contain Chlorella. Density of Chlorella should be around 300 000 cells per ml. Fujimura (personal communication) suggested 1–1.5 million cells per ml. The newly hatched larvae are transferred into these tanks. The larvae has high tolerance to the salinity difference. According to Fujimura (personal communication), the larvae might be transferred from freshwater to water salinity of 21 ppt without serious damage. But the larvae is sensitive to the temperature difference, so it is better if the newly hatched larvae should be acclimatized slowly into the hatchery tanks. Density of larvae in the tanks is around 20 per liter.

In hatchery tank of 6 × 1.5 × 1 m, larvae at total number of 180 000– 200 000 can be stocked. These comes from 9–10 berried females. To fill one tank with 200 000 larvae sometimes takes 4–7 days, strong aeration should be provided. Starting from day 2, the larvae can be fed with prepared feed which should be screened very finely, approximately 0.2 mm mesh size. The prepared feed may be a formulated feed with the following composition:

The amount of feed is 1 g per 5 000 larvae/day, and then gradually increased to 5 g/5 000/day, the feed is given 4 times a day. The following schedule may be followed:

The feed may be divided into four portions which can be given at 0730, 1130, 1440 and 1600 hours. At the late afternoon, one-day old brine shrimp nauplii can be fed to the larvae. The amount of brine shrimp given is 5 g/ tank/day on 1–10 days, and from day 11 onward the amount is increased up to 10–20 g/tank/day of two-day old brine shrimp nauplii. Put brine shrimp eggs into buckets of 60 liters with strong aeration. After the eggs hatched, the nauplii are poured into the hatchery tanks. For the two days old nauplii, after the eggs hatched, add 2 liters of greenwater to feed the Artemia.

Examine the larval condition after feeding whether each individual has ingested some food particles, if necessary put some more food. Each tank should be cleaned from leftover food, dead plankton or fecal deposit. Twice a day the tanks should be cleaned from this material by siphoning. To do this, the aeration should be stopped for a few minutes, so that all particles will deposit on the bottom, then start siphoning. Examine larval stage everyday and also monitor the water temperature, ammonia concentration in the water. If the ammonia concentration exceed 0.5 ppm, replace one-fourth volume of the water from the tanks bottom with fresh greenwater from the supply tank. Or if the greenwater in the tank becomes clear, reduce one-fourth volume of the water from the tank bottom and replace with greenwater from the supply tank. Cover the tank in the evening to prevent the water temperature from decreasing during the night.

When post larvae (PL) appears, collect the PL by separating them from the larvae and transfer into freshwater tanks by gradual adaptation to the media. This work should be repeated every five days until a few larvae is left - then drain the tank completely.

1.4 Post larval care

The PL, after being selected among the larvae, should be adapted slowly into freshwater. Put the PL in a bucket or tub with strong aeration. Reduce water from the bucket by siphoning using a small plastic hose. While reducing, add freshwater slowly with another small plastic hose. Usually acclimatization takes place around 3–4 hours. When the salinity in the tub is zero, the PL is then transferred into tanks with freshwater.

The nursery tank is maintained as raceways, so that high survival rate of the PL will be attained.

The fry were fed on pelletized feed with 22% of protein. Leftover food should be siphoned out everyday.

1.5 Fry transportation

The Macrobrachium fry was transported in plastic bags inflated with oxygen. It is transported when they are found 1.5 cm in length (from tip of rostrum to telson). Volume of water in plastic bags around 1–5 liters and oxygen volume around 2–8 liters. Results of trial transplanting are shown in Table 3.

SELECTION OF SUITABLE FISHPOND SITE FOR THE CULTURE OF THE GIANT FRESHWATER PRAWN MACROBRACHIUM ROSENBERGII

by

Juan V. Lopez¹

1. INTRODUCTION

In the various Southeast Asian countries, fish culture development has to some extent improved at varying degrees and level of technology, particularly in Indonesia, Malaysia, Thailand, China, and the Philippines. These countries have extensive idle and unproductive swamp areas. Most of them are now developed into productive ponds, most of which produce fish, a cheap source of animal protein for human consumption. However, with the inception of the culture of crustaceans, particularly the giant freshwater prawn (Macrobrachium rosenbergii) and jumbo tiger shrimp (Penaeus monodon), there is a great clamor and demand of these species in the world market due to their high nutritive and market value. With the favourable weather conditions in most of the Southeast Asian countries, there is an urgent need to develop at a fast pace and improve the technology of the culture of crustaceans and ultimately the production of more of these highly nutritious crustaceans to cope with the ever increasing demand in the local as well as foreign markets. The progress of the culture of the freshwater prawns in less than 20 years is a giant leap towards a much greater pace in the production of a highly nutritious freshwater crustaceans, Macrobrachium rosenbergii. Historically, freshwater prawn culture came to existence in Malaysia with the pioneering work of Dr. S.W. Ling. Since then, a worldwide interest among aquaculturists is now underway in several countries.

2. SELECTION OF SUITABLE FISHPOND SITE FOR GROW-OUT PONDS

One of the most important factors that contributes to the success of the culture of the giant prawn is selection of suitable site. However, one should be guided with the types of pond culture to use and the nature of water supply available.

In the selection of a farm pond site for the giant prawn, factors to be considered are as follows:

¹ Fishery Biologist, FAO/UNDP Brackishwater Aquaculture Development Project, Jepara, Indonesia.

2.1 Water supply

In the selection of a freshwater fishpond site, source of water supply must be given careful and meticulous consideration. It determines the general water supply of the whole pond system in relation to the total requirement of the project. The source of the water should be diverted into the pond with the maximum use of its rate of flow.

Three systems relative to water supply to be adopted are as follows:

1. Topography in relation to supply of water by gravity;
2. Use of mechanical power (pumps, windmill, etc.; and

3. Combination of both (a) and (b).

In the determination of the type of culture and level of production, the kind and amount of water supply plays an important role in the achievement of a specific purpose.

2.1.1 Three types of water supply

1. Artesian well (surface well and free flowing artesian well)

   1. Surface well of about 2–5 m deep - Water can be drawn from the well manually, by water pump (lift) or by electric water pump. This may be affected by pollution.

   2. Deep well - Sinking of GI pipes of about 80–200 m deep could draw out water with an electric water pump depending on depth of water table. It may be free from pollution but with less amount of oxygen.

   3. Artesian well with free flowing water - GI pipes are sunk underground to the water table and water oozes out freely. It is free from pollution but less amount of oxygen and free from micro-organisms that may cause diseases to the cultured animal under controlled conditions.

2. Rain fed depressions located in between low hills in uplands

   The three elevated sides act as natural embankment and the fourth side is a level area to be provided with embankment and corresponding gate for control of water. Depending on the amount of rainfall, watershed of about 5 ha may supply a one-hectare farm pond with sufficient water. Rain and its runoff water is suitable for fish farming in a lowland area or in a depressed plain. This stagnant water could be utilized for growing natural food for the stock to be cultured.

3. Most suitable type of water supply for grow-out ponds is the spring, brook or stream water with continuous flow all the year round and must be free from pollution. These sources of water supply could be diverted into the earth pond, running water pond, raceways, etc. Each area may be arranged as follows:

   1. Raceways in series
   2. Running water ponds

   3. Farm ponds or sky ponds

2.2 Quantity of water supply

Sufficient continuous water supply of good quality is the most important factor in pond culture.

2.2.1 Quantity of water supply is grouped into:

2.2.1.1 Stagnant water. This is supplied mainly from rainfed watershed areas. The volume of water needed is sufficient to compensate for the losses due to seepage and evaporation of water in the pond.

2.2.1.2 Ponds with continuous flow of water at the rate of 2–5 liters per second per ha may be grouped into free flowing. Aside from the sufficient volume of free flowing water, it supplies well oxygenated new water into the pond.

2.2.1.3 Extensive volume of water supplied at the rate of 100–500 liters per second per pond (50 – 500 m²) is called running water.

Generally, the requirement/volume of water are as follows:

Where there is limited water supply, maximum production could be attained with the adoption or use of special equipment such as water pumps (electric), recirculating system, blowers, or other devices that could aerate the water to maintain good and sufficient amount of oxygen in the water.

2.3 Water quality

2.3.1 Direct water supply from well or spring could be a dependable source for the freshwater pond, although the natural productivity and O₂ content may be low while CO₂ and N are normally high. Besides, most of these waters are free from micro-organisms, parasites, undesirable species, pollution, etc.

2.3.2 The most commonly used water in farm pond is the surface (runoff) water. It is the cheapest source of water supply usually with abundant minerals and nutrient elements. Also, it is suitable for extensive and semi-intensive culture. However, problems may be encountered due to possible contamination of diseases, parasites and pollutants.

2.3.3 Water rich in organic matter may have much higher production (4–12 tons) if improved techniques could be implemented. These include the selection of compatible species to be cultured in the same pond, systematic culture and harvest, use of aeration devices, prevention of sedimentation, etc.

Classification of water hardness by parts per million of CaCO₃

2.4 Topography

One of the main criteria in the selection of grow-out pond site is topography.

2.4.1 The most preferable area is an ideal flat land with slight inclination of bottom elevation for easy drainage.

2.4.2 Agricultural land with regular shape and extensive enough for future expansion is ideally suitable for farm pond. Undulating, hilly area and/or rolling uplands have small and irregular shaped pond.

2.4.3 River basins, deltaic areas and depressed lowlands must be properly surveyed and evaluated to determine their economic viability.

2.4.4 Proper drainage of the pond system is a critical factor in the selection of pond site. Topographic condition of the area should permit complete drainage and drying of the pond system for effective exposure of pond bottom in sunlight.

2.4.5 A suitable pond site must be an area free from the occurrence of flood waters. Most of these areas are located in the river basins, deltaic areas and depressed lowlands and therefore intensified presurvey is required to determine feasibility of the project.

2.5 Quality of soil

Two important factors for consideration in pond construction are:

1. Soil fertility, and

2. Water retentivity

2.5.1 Soil fertility to some extent is not a serious problem. Although it is important in the determination of area for extensive and semi-intensive culture, it is of secondary importance in intensive culture.

2.5.2 Permeability or imperviousness of soil. Clay, sandy clay and/ or clay loam soils are impervious and seepages are very limited or none at all, therefore must be given priority in the selection of pond site. Area with soil admixture of coarse sand/or gravel, organic and decomposing matter must be avoided.

3. SUMMARY

The selection of freshwater fishpond site calls for a rigid and systematic survey and observation of the correlated elements involved, such as soil characteristics, weather conditions, etc. Flooded area must be avoided because it entails greater risks and expenses on the design and construction of pond.

As fishery biologist, selection of anyone of the system must be based on the following salient factors, in addition to the above-mentioned facts:

1. Relationship of water volume to

   1. Extent of pond area,
   2. Depth of pond, and

   3. Pond requirement for management technique.

2. Foundation, elevation and nature of soil
3. Ground water as to its elevation

4. Availability of pond construction materials

In addition to the major factors in the selection of site, other elements to be considered in a region of socio-economic nature are as follows:

1. Prevailing economic condition of community where site is located
2. Transportation
3. Population density

4. Availability of stock

4. REFERENCES

Ling, S.W. and T.J. Costello. 1975 Review of culture of freshwater prawns, FAO Technical Conference on Aquaculture, Kyoto, Japan, 26 May – 2 June 1976

Lopez, J.V. 1974 Present status and problems of prawn culture in the Philippines (BFAR mimeo), 1974

LAYOUT AND CONSTRUCTION OF GROW-OUT PONDS FOR PRAWN (Macrobrachium rosenbergii)

by

Bambang S. Ranoemihardjo¹

1. INTRODUCTION

Freshwater prawn (Macrobrachium rosenbergii) are found in tropical and sub-tropical regions. Generally, they are found in lakes, rivers and swampy areas with fresh- or brackishwater. Nowadays, several fish farmers culture prawn in freshwater ponds. Juveniles of the prawn may now be acquired from hatcheries for culture. There is a developed hatchery technology. Then the juveniles are stocked in freshwater ponds and cultured up to marketable size.

Ponds for growing the juveniles have similar conditions with freshwater fishponds. Besides, the prawn can be cultured from lowland to upland plains to about 600 m above sea level. Favourable conditions of the pond will result to high production, especially if coupled with good management. Conditions needed for prawn culture are as follows: good water supply, favourable type of soil, suitable condition of pond itself, etc. Fish farmers prefer earthen ponds than others, because the cost of construction is lower.

The following paragraphs will explain about grow-out pond layout and construction.

¹ Chief of Culture Technique Division, Brackishwater Aquaculture Development Centre, Jepara, Central Java, Indonesia.

2. LAYOUT OF PONDS

Ponds are bodies of water that are usually man-made and resemble a size smaller than a lake. These are built and are made of soil embankments if the topography is not levelled. But if the area is levelled, these are built by excavation.

2.1 Shape and size

Generally, a pond for prawn culture is rectangular in shape; practices show that the width of the pond could vary from 2 to 20 m, and the length varies from 3 to 30 m. The ideal size for prawn culture is 2000 to 3600 m² (Fujimura, 1974) or 1000 m² (Ong, 1977). Pond size for freshwater fish and prawn in Indonesia are usually about 500 m² only. The size of the ponds in Hawaii are much larger than the common freshwater ponds in Indonesia. The reasons are: (i) building of pond by machineries or buldozer; (ii) operations during harvest with gillnets; and (iii) according to experience, the productive area of a pond is near the dikes. There are different sizes and shapes of a pond. The general layout is shown in Fig. 1.

Water depth in the pond is about 0.5–1.5 m with sufficient water supply for the whole year. It must be free from flood. A pond for prawn culture should be easily filled with water and could be drained completely. Pond bottom must be level, so that gillnet operations is easier during selective harvest. Another model of pond should have a bottom with peripheral and centre ditch, it will be much easier to drain completely for total harvest. Besides the ditch could act as shelter for the prawn when the water is too low.

2.2 Water

Water supply for aquacultural enterprises must meet both in quantity and quality requirements. Water quantity must be sufficient to make up for evaporation and seepage losses, supply the necessary amount of oxygen, and provide enough flushing to remove waste products. Water quality for aquaculture must meet rather high standards. The temperature, oxygen content and hardness must be at optimum levels for the crop. It must be economically feasible to alter them to these levels. Pollution and undesirable organisms in the water supply must be eliminated. Nutrient contents of the water should be as near as possible to the optimum levels for the crop. Nutrients may be added to the water to bring the level up to optimum conditions.

Surface water sources (e.g. streams, lakes, ponds) are commonly found in Indonesia, all exhibit greater variations in environmental parameter with time than ground water sources. Surface water is usually high in oxygen concentration when compared to ground water. Greater risk exists for pollution problems when using surface water sources.

The volume of incoming water is not only to compensate the water losses due to seepage and evaporation, but in addition it supplies new and well oxygenated water. In tropical waters the loss of water is estimated at 3 liters/second/ha. In general, the required quantity of water is as follows:

Pond supplied with water rich in organic matter may produce high yield, provided some effective culture system is adopted, e.g. use of detection, sedimentation and filtering devices. Optimum of water temperature for prawn is 28° – 31°C, and it should have high oxygen content. The range of water pH is 7.5–8.5 or slightly high alkalinity.

2.3 Soil

Soil type is important in determining the selection of pond site. The soil must have a low permeability, if soil bottom and sides are to be used for the ponds. Otherwise excessive water loss from seepage will result or expensive sealing procedures will be required. The soil fertility is not always the major factor, especially in intensive culture, it is of secondary importance. The water retention plays a more distinct role. Clay loam, sandy clay or clay are most suitable.

Ong (1977) explained that muddy soil is suitable for prawn culture, but Fujimura (1974) did not agree with muddy soil. The reason is that at night time, concentration of oxygen is low and it is more difficult to harvest. By manuring the pond and supplementary feeding, a poor soil could be enriched and may be used for prawn culture. The composition of soil determines the water retention capacity of the dike and bottom. It is advisable to select homogenous clay and avoid mixing it up with coarse sand, stones or organic matter.

3. POND CONSTRUCTION

There are two ways of pond construction, the dug out and the levees. The latter type is attained by damming. This is preferable, since it retains the fertile top soil and is less costly. For extensive and large ponds, usually it is preferable to use buldozer, but for small ponds, by manual only. In order to retain the fertile top soil, this has to be piled up in mounds or in one place and later spread it over the pond bottom.

3.1 Preparation

After a careful evaluation of the site, it is possible to determine the construction of one or more ponds. But this will depend on the type of farming and the nature of the ground. If the pond is to be built on deep clay soil, the dike can be several meters high, but if the soil is porous the height will be limited. When several ponds are built, it is advantageous to see that each one has its own supply and drainage systems. Water supply in each pond is independent and can be emptied at will.

Before construction, all vegetation should be removed particularly along the path of dike. It is very important because part of the trees left will make the dike weak and/or seepage starts as soon as the roots begin to decompose.

In Indonesia, the traditional tools used by fish farmers to construct a fishpond include - e.g. pakul, spade (Fig. 2).

3.2 Dike building technique

The dike is a very important part of a pond. In fact a badly made dike will cause irreparable loss of the much needed water. Dike must be built with the greatest care. The two principal qualities are its solid state and water tightness. Dike should be built along a fixed contour of the plain. The profile of the dike could be followed with the use of bamboo framework previously prepared.

If the ground on which the dike is to be built is sandy, gravelly or marshy then it will be necessary to dig deeper to reach the solid water-tight foundation. At start, the grasses, rooted vegetation and top soil, peaty lump and organic matter are removed from the site. If the soil is sandy, the width of the dike must be doubled or a clay core, from 40–50 cm. thick should tie the dike into the water-tight ground (Fig. 3).

Sandy clay is the best material for dike construction. Turf, humus or peaty earth should be avoided. Eliminate stones, wood or any other materials which might decompose or rot. If the soil is too compact, then it can be made usable by mixing it with humus. If pure clay is used, it must be covered with some other materials in order to avoid cracking when it dries up.

Dike should be built in layers of 20 cm and each layer must be rammed down. Dry earth must be moistened. In principle the width of the dike at the top (crown) should be equal to its height but should never be less than one meter wide. The dike must be some 30 cm above surface of water for small ponds and 50 cm for larger ponds.

Shrinkage must be taken into account and can reach as much as one-tenth of the height. For this reason, the final height after construction is generally greater than the original specification to give allowance for shrinkage.

In general, the dike-slope is 1:1 to 1:1.5 (vertical to horizontal), but in some places in Indonesia the slope is much more steeper and the crown is more or less 0.5 m only. The final step in dike construction is smoothing and leveling of the irregularities. Grass planting would impede erosion. Trees should not be planted on the dike because the roots can cause water to seep through. If the dike is constructed carefully then the slight oozing of water which might be noticed at first may disappear once the pond is filled with water and the dike becomes watertight.

During dike construction, the location of sluice gate must be left free. It is often felt necessary, that dikes are made wide enough to allow passage of vehicles for transporting supplies and materials.

3.3 Sluice gate

Each pond compartment must have a water inlet and outlet except ponds fed by spring. An overflow should be provided for excessive water supply. A well-constructed water inlet must fulfill the following conditions: (i) it must assure a regular and well regulated supply of water for the pond; (ii) it must prevent the escape of fish or prawn especially the possibility of their escape through the water outlet; and (iii) it must keep out undesirable fish which might come in through the water leading into the pond. To protect the fry, a single or double screen can be installed at the mouth of the water inflow of each pond. Water inlets can be constructed in different ways according to general inflow for a group of ponds or as an individual inflow for one pond.

3.3.1 Water inlet

The best general water inlet is known as an inlet with sunken horizontal screen (Fig. 4). This type meets the three conditions outlined above. The advantage of a sunken horizontal screen is that it stays much cleaner than a vertical screen or an oblique screen. The latter gets chocked too quickly and has to be cleaned frequently, which is not always possible. A chocked vertical or oblique screen through which the water passes is just a sunken obstacle and is sufficient to prevent the escape of the fish or prawn from the pond or keep out intruders.

For the horizontal screen to function normally, it must be sunk and covered with 10 cm or more of water. The fact that the screen is sunk, some of the debris, leaves, twigs, etc. brought by the water remain on the surface and do not stick to the screen. This means that there is always a free section.

The simple outlet is one with the use of pipe with screen at end. Sometimes, a fish farmer installs a wooden gate (Fig. 5) with bamboo screen. While allowing the water in through the screen, water fall, thus increasing the oxygen content in the pond water.

3.3.2 Water outlet

The simple water outlet construction is a bamboo or PVC pipe and set vertical pipe system. It is very easy to adjust the depth of pond water as desired by moving the pipe. The most common and effective type is the monk (Fig. 6). The device performs two functions: (i) regulation of the desired depth of water while preventing escape of fish and prawn; and (ii) complete drainage whenever necessary. The “monk” is constructed and placed off the dike. Unlike a sluice gate, it is placed in the dike. It is made of concrete with three side-walled device, one side left open in the direction of the pond proper. At both and opposite side walls, two to three pairs of groves are made; the first one is where the screen is to be placed and the second and eventually the third one, the wooden slabs. The monk is used to regulate the water intake; it can take bottom water layer or surface layer by adjusting the second board. The monk is connected at the bottom to the drainage canal by a concrete pipe, which runs along the full length of the base of the dike.

3.3.3 Drainage

Usually the pond bottom has a slope with slight inclination to make draining much easier. Slope is about 100 : (0.5 – 1), that means every 100 m there is a difference of level about 0.5–1 m. Beside the slope, there is a longitudinal or diagonal ditch connecting the inlet and outlet. The width at the bottom of the ditch should be 0.5–1 m and the depth more or less 0.5 m, becomes wider and deeper towards the outlet. In a small pond one ditch is sufficient.

A large pond must be provided with secondary ditches or with a peripheral ditch. It is important to design the outlet so that the pond can be drained within about 48 hours. The functions of the ditch are: (i) to enable complete draining and drying of the pond bottom; (ii) to enable cropping of the fish or prawn alive; and (iii) to provide shelter during critical times.

4. REFERENCES

Adisukresno, S. 1980 Pedoman pemeliharaan udang galah. Direktorat Jend. Perikanan. Balai Budidaya Air Payau, Jepara. 21p. and figures

Djajadiredja, R. and Soetardjo Natawiria. 1975 Guidelines for prawn culture. Directorate General of Fisheries. Brackishwater Aquaculture Development Centre, Jepara, Indonesia: 22p. and figures.

Fujimura, T. 1974 Development of a prawn culture industry in Hawaii. U.S. Dept. Commerce, NOAA, Nat. Marine Fish. Serv. (Job Completion Report). 21p. and figures

Hechanova, R.G. and B. Tiensongrusmee. 1980 Report of assistance on selection of site, design, construction and management of the Ban Merbok, Kedah, Malaysia Brackishwater Aquaculture Demonstration Project. Manila, South China Sea Fisheries Programme, SCS/80/WP/88. 154p.

Huet, Marcel. 1971 Textbook of Fish Culture. Breeding and Cultivation of Fish. Fishing News Ltd., London, England. 436p. and figures

Ong, K.S. 1977 Prospects and problems of Macrobrachium. First ASEAN Meeting of Experts on Aquaculture: Technical Report, 13 January-6 February 1977, Semarang, Indonesia. 143–147p.

Wheaton, F.W. 1977 Aquaculture engineering. Wiley - Interscience Publication. John Wiley and Sons, New York. 708p.

Figure 1. General pond layout for prawn (Not to scale)

1. Dike
2. Inlet
3. Diagonal ditch
4. Outlet
5. Pipe (Bamboo or PVC)
6. Stand pipe (Outlet pipe)
7. Screen

8. Concrete foundation

Figure 2. Traditional tools

Figure 3. Cross section of dike with puddle trench

Figure 4. Constant flow water inlet with sunken horizontal screen

Figure 5. Type of wooden sluice gate

Figure 6. Monk type for pond outlet