|AFRICAN REGIONAL AQUACULTURE CENTRE, PORT HARCOURT, NIGERIA|
|ARAC/87/WP 12 (14)|
|CENTRE REGIONAL AFRICAIN D'AQUACULTURE, PORT HARCOURT, NIGERIA|
P. G. Padlan
Lectures presented at ARAC for
the Senior Aquaculturists course
UNITED NATIONS DEVELOPMENT PROGRAMME
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND MARINE RESEARCH
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2. Biology and ecology of the penaeid shrimp
3. Penaeid shrimp found along the coasts of Africa
4. Farming systems
5. Factors to be considered before going into pond farming of shrimps
6. Site selection criteria
7. Layout and construction
8. Shrimp fry
9. Pond preparation
11. Water manipulation
12. Artificial feeds
14. Harvesting and post harvest technology
15. References for further reading
Traditional shrimp farming could have started about three centuries ago * in brackishwater fish farms in the Far East and even now continues to exist in some parts of the region. This forerunner of the present improved practices was a very low technology (or art) involving trapping, growing and finally capture of the animal when the ponds are drained. Shrimp then were regarded as a minor product which grew in association with other finfish and products of commercial value. Development of shrimp farming to the point of sophistication in very highly intensive operation came about only during the past two or three decades due to high demand, first of live shrimp in Japan, later to consumer preference in developed countries. More demand, a growing decline in shrimp fisheries due to over-fishing, pollution and the high cost of shrimping as well as the need for foreign exchange by developing countries have contributed to the growth of shrimp farming in tropical areas.
* Extensive shrimp farming in paddy fields arround lagoon and backwaters in Kerala and Bengal in India has been existing from historical times.
Potential areas for shrimp farming cannot at present be quantified. In the Far East, tide-fed brackishwater farms total more than 400 000 ha, distributed as follows: Indonesia, 190 000; Philippines, 180 000; Taiwan (China), 16 000. While present technology may not be appropriate in all the these ponds (most are dedicated to milkfish culture) future developments make these areas highly potential particularly if the demand for shrimp continues. Farmed shrimp now constitutes about 4.5% of total world production of about 1.7 million metric tons and is contributed by the following countries: In Asia, India, 15 000 (estimated); Indonesia, 11 313; Taiwan, 9575; Thailand, 10 091; Philippines, 3 900 (for 1981); China, 1 400 (estimate); Malaysia, 157; and South Korea, 100 metric tons.
In Latin America: Ecuador, 21 500; Brasil, 200 (estimate); Panama, 1 500; Honduras 250 (estimate); Guatemala, 100 (estimate). In the Caribbean: Martinique, 150 (estimate); Jamaica, 25 (estimate). Above figures are for 1982 unless otherwise stated. Considerable increases have been made since then, especially for Ecuador which now has been reported to have exceeded 50 000 metric tons. Similar increases have been reported for Taiwan. The figure for Japan is not included as all production goes to local consumption.
Penaeid shrimp are with a few exception marine. Some of the marine shrimp spend part of their life cycles in brackishwater estuaries. The life cycle goes through several stages of development: from fertilized egg to nauplius to zoea to mysis to post larva to juveniles and finally to adult (Fig. 1,2 & 3). Sexually mature shrimp spawn in the deeper marine waters. The eggs are fertilized as they are extruded by sperm earlier deposited in the female's thelycum during mating following moulting of the female. The male sexual organ is the petasma. Fecundity differs with species, ranging from about 46 000 for Metapenaeus mutatis of about 12cm length to about 1 128 000 for Penaeus monodon of from 25 to 28 cm. Through the larval stages, the nauplius reaches juvenile stage while migrating to the shallower coastal waters where vegetation provides nursing grounds for their development. Reaching sub-adult, they return back to the sea, becomes mature sexually and the cycle is repeated. Growth follows each moulting. It is during moulting that the shrimp is helpless and vulnerable to predation.
Fig. 1. Penaeid shrimp. 1. Rostrum, 2. Rostral spine, 3. Post-obital spine 4. Hepatic spine, 5. Carapace, 6. 1st abdominal segment, 7. 6th abdominal segment, 8. Telson, 9. Uropods, 10. Pleopods, 11. 5th pereiopod, 12. 1st pereiopod, 13. Antenna, 14. Antennal spine, 15. Antennal blade, 16. Antennulal flagella.
Fig. 2. Post larvae of penaeid and carid shrimps. Note the difference in the overlap of the numbered segments and chelate legs
J - Juvenile
As - Adolescent
SAd - Sub Adult
Ad - Adult
Sp - Spawner
E - Eggs
N - Nauptius
P - Protozoea
My - Mysis
Mg - Megalope
Fig. 3. Life cycle of Penaeus monodon
Food of shrimp ranges from plankton to small invertebrates. The nauplius thrives on the egg yolk. Zoea feeds on phytoplankton, generally diatoms. From the mysis to maturity, animal protein is required. The food of P. monodon in the wild has been found to consist of crustaceans (mainly small crabs and shrimp) and mollusls making up 85% of the ingested food. The remaining 15% consists of worms (annelids) and others.
Environmental requirements also differ with different species. While the larvae have very wide range of salinity tolerance (P. merguiensis for instance have been found, under laboratory condition to tolerate from 2.61 ppt to 60.49 ppt; P. monodon larva tolerates up to 71 ppt). It has further been observed that optimum salinity for P. monodon growth in ponds is between 15 to 25 ppt while that for P. indicus or the Indian white shrimp is from 20 to 30 ppt. P. monodon and P. inducus have been observed to telerate much higher salinities in ponds. In Malindi, Kenya, for example, P. indicus have been cultured where salinity reach nearly 60 ppt just before water can be exchanged. The ideal pH is neutral to slightly basic. P. semisulcatus has been observed to be adversely affected when dissolved oxygen falls to 2 ppm and continues in this state for several days; for P. monodon, the critical concentration is 2.7 ppm. Temperature-wise, P. monodon thrives best at between 28 – 33°C; P. indicus begin to die at 34°C; P. semisulcatus is tolerant to low temperatures in Taiwan and can continue growing at 22°C. P. japonicus cannot tolerate above 30°C. P. monodon, P. indicus, P. merguiensis, M. monoceros and M. ensis prefer and mud bottoms; P. japonicus prefers sandy bottom.
Holthuis lists 19 species in East Africa. Of these, four (M. monoceros, P. indicus, P. japonicus and P. monodon) have been proven culture species while two (P. semisulcatus and P. latisulcatus) are still under tests elsewher. In West Africa, five species are commercial catches. Experiments have been conducted on P. notialis. This species as well as P. kerathurus, Parapenaeopsis longirostris and Parapenaeopsis atlantica (Fig. 4) are found also in Nigeria.
Three systems - extensive, semi-intensive and intensive are practiced. While there are wide divergences in the manner with which these are accomplished, each has its common denomination which makes it a system apart.
Extensive system generally involves wide ponds with very little operational inputs (fry and fuel for pumps as may be required). Quite often, it is undertaken in polyculture with other finfishes in the Far East, monoculture (in principle) in Latin America. The extensive system relies mainly on the natural fertility of the soil and water and the amount of extraneous feed which the water brings along as it enters ponds. The size of the ponds in Ecuador can range from 10 ha up to 100 ha.
The semi-intensive system involves a more systematic and scientific approach which involves the use of fertilizers to increase natural food and feeds to supply adequate nutrition. Feeding, however, may be minimal, at best supplementary. The use of these additional inputs pave the way for higher stocking rates. Partial water exchange is also necessary to keep conditions more or less within optimum and tolerable limits of the organisms. Pond areas vary from 1 to 10 ha.
Fig. 4. Penaeidae: A - Parapenaeopsis atlantica
B - Penaeus kerathurus
C - Penaeus notialis
(modified from Crosnier and Bondy, 1966 -courtesy C. B. Powell)
The intensive system relies on feed alone from external sources, aeration, regular water exchange (daily), or a constant flow through of new water, to be able to support a very high population. The intensive system is a very sophisticated technology requiring monitoring constantly, therefore applicable to smaller areas, usually from 1 000 to 10 000 m2.
One goes into aquaculture for profit unless certain considerations are more supreme, e.g. improvement of the socio-economic welfare of rural population through generation of employment (often state organized). Governments of developing countries also encourage shrimp farming as a source of foreign exchange. The second criteria is: What would be the target species and is there a proven technology? Were it for profit, the third consideration is: Will it be economically viable granting it is technically feasible under local condition? Are there sites available?
The following criteria should be considered in site selection: 1) soil, 2) water quality, 3) water adequacy, involving study and observations of tidal patterns and amplitudes, 4) land elevation, 5) vegetation, 6) availability of man-power, 7) availability of supplies and equipment for construction and operation, 8) communication and accessibility for effective management and 9) ready outlet. The best type of soil is clay-loam or sandy clay as these make good and strong dikes. Peat is to be avoided, also soils with high potential acid sulfate. Water should be clean, unaffected by pollution. The rule of thumb: given a choice, would one want to swim in such waters? Water adequacy would depend upon the tidal amplitude and the elevation of the land.
Stand and species of trees should also be properly evaluated. Cost of construction would be lessened if the trees are spares and of the shrubby type. Rhizophora generally indicate acidic soils where the stand is very thick; Avicennia, good soils with sufficient amounts of clay. Availability of supplies and equipment for construction and operation determines not only the cost but also the time involved.
Communication and accessibility for effective management is also a must. Where operations have become established and routine, communication and accesibility would play and important role. Fish farmers could benefit from two-way radios that could do away with unnecessary visits only for the purpose of checking up with the technicians or minor matters. Good roads and waterways should make accessibility much easier.
Ready outlet - Organized marketing through brokers, cooperatives or direct to exporters would be needed for bigger farming operations. This is the most important part of the exercise, and the business. Success in marketing determines the bottom line of shrimp, and other commercial aquaculture.
For ponds in the inter-tidal zone, a proper layout should be prepared to include features needed to give the target animals suitable growing conditions with economy in cost of both construction and operation taken into account. Management system envisaged should determine such layout (Fig. 5A & B).
Extensive, single phase system - The ponds required consists only of grow-outs where fry are stocked, grown to marketable size and then harvested. Main dikes and inlet and outlet gates are the minimum requirements. Where water has to be taken in by pumping, pumps would be required. Semi-intensive, two-phase system would require nurseries, in addition, and pumps as a must. Supply and drainage canals are now incorporated here. Intensive pond system as in Panama has a reservoir, acting also as a supply canal, from which nursery and grow-out ponds radiate. In Taiwan, the availability of fresh water to tone down salinity to optimum conditions for P. monodon is a must. A hatchery will be needed to supply the fry in large scale operations.
Fig. 5A. Layout for a shrimp farm using a monocultural system in Thailand (After Cook, 1976)
Fig. 5B. Layout for a shrimp farm as proposed in the Philippines (After Santos, 1978)
Steps in the preparation of the layout involves clearing, to establish lines of perimeter dikes, survey and plotting of the area, detailed observation of water depth at high tide at various places to give an idea of how ponds, canals and dikes are to be located. Familiarity of the area this gained will be of much help in the preparation of the layout in accordance with the farming system planned.
Perimeter dike paths are cleared of trees and roots as well as a substantial area adjacent to it where soil could be excavated for dike construction fill. A puddle trench is dug along the center to reach depth beyond the planned level of the pond bottom, and packed with good, impervious soil. This would avoid leaks resulting from decaying lateral roots later on. Since the area will be under water during high tides, the perimeter dikes are constructed first to be able to enclose the whole area and give workers freedom to work undisturbed by high water. As a general rule, the best period to construct dikes would be when the high spring tides occur during the evenings. The lower low tide and the lower high tide that follows at daytime would either expose the land or inundation would be minimal.
Manual labour is generally used for starting construction.
The ponds in Indonesia, Philippines and Taiwan were constructed mainly with manual labout. Heavy equipment are now utilized. Clam shovels and drag lines, the former on pontoons, the latter on wooden ties have been employed. Bull dozers, particularly those especially built for soft land are now in the market.
Creeks are dammed first, then gates are set. Leaving these last will concentrate the whole volume of water coming in or out in the former and result in much more difficult work, needing the concentration of more labourers. Pre-installed gates would provide water into the area as needed for construction work and/or drain the area if required. Once enclosed, clearing of the rest of the vegetation is done, the internal dikes completed, the secondary gates installed. A topographic survey of the bottom of each pond should enable constructors to determine the degree of cut and fill where leveling is required. Once all these are done, ponds are ready, unless stabilization would further be needed.
Fry are most often acquired from the wild. In Thailand, where shrimp farms exist, the waters in the estuaries teem with fry, mostly P. merguiensis. The same had been the case in Ecuador during the early start of the industry there. In both countries, fry enters the farm ponds as water is pumped or allowed into the area. Otherwise, fry are caught by fry catchers with the use of 1) stick nets, 2) scissor nets, 3) lures and dip nets, 4) set traps, 5) beach slines, 6) mobile “sweepers” or “dozers”.
Fry are sold directly to shrimp farmers by the catchers if the latter have sufficient quantity of catch.
Otherwise the catchers, with say, 100 or 200 fry caught (as with P. monodon) during a spring tide cycle, or during a diurnal cycle, would sell their catch to a fry dealer who collects these, accumulate and hold these for farmers who would need large quantities at one time. Fry may also be acquired from established hatcheries which could produce fry from gravid females, either wild or matured in controlled condition. Gravid females from the sea are however preferred over those that have been grown to maturity as the hatching rate is much higher. Matured females are eye-stalk ablated to hasten development of the ovaries. More work along this line is being conducted.
Pond preparation includes draining and exposure of the pond bottom to the air until the bottom cracks and some degree of soil mineralization takes place. All fish and other organisms that might become predators, pests or competitors are eliminated by poisoning with highly degradable pesticides (saponin from tea seed cake at 1.1 ppm or more; rotenone at no less than 0.2 ppm).
Organophosphate insecticides like Gusathion at 0.1 ppm of the product have been used successfully. However, these are to be applied with caution as these are highly toxic to the user. Snails are very hard to eliminate by merely drying or use of saponin or rotenone but they have been observed to die when the water go beyond 70 ppt salinity. Tri-phenyl-tin compounds which are sold as fungicides have been found to kill snails (Cerithidae) at a concentration of 0.15 ppm but this compound takes very long to degrade.
Where natural food is to be augmented with fertilizers, organic fertilizers or inorganic fertilizers or a combination of both are applied.
In the case of benthic algae, chicken manure is best, followed by pig manure. Although benthic algae are not all of use to the shrimp, small invertebrates that congregate and browse on it becomes valuable food for the shrimp. Filamentous algae and other higher aquatic plants (Ruppia or Chara) also attract these browsing organisms, and are also encouraged, where conditions are not conducive to growing other food but good for these plants.
Application of fertilizers enhances the vegetative growth of these higher aquatic plants, hastens their maturity as well, depending on the type of nutrients applied (nitrogen for growth, phosphorus) for maturation). Detrital algae and Ruppia or Chara are sought more by the small invertebrates.
Culture of benthic algae requires a number of operation and includes 1) drying of the pond bottom to the right hardness, 2) application of organic manure, 3) initial watering, 4) evaporation of the water let in, 5) another drying of the pond bottom, 6) second watering, 7) application of inorganic fertilizer and 8) gradual raising of water depth.
Culture of filamentous algae is undertaken along the following steps: 1) exposure of the pond bottom until the ground starts to crack, 2) seeding with algae or mature Ruppia and/or Chara (where seeds have already formed) 3) filling to shallow depth with water, 4) application of small amount of organic and inorganic fertilizers and 5) nursing the growths while increasing water depth.
Organic fertilizers are cow dung, horse dung and even rice bran. The last mentioned has been observed to trigger rapid growth of benthic algae in Taiwan.
Chemical fertilizers include single element fertilizers (ammonium sulfate, urea, superphosphate, Triple-superphosphate). Muriate of potash is not necessary. Mixed chemical fertilizers include ammonium phosphate and diammonium phosphate. In the absence of mixed fertilizers as the above, complete fertilizers (containing N, P and K) are used but with these, K as mentioned before may just be wasted.
Chemical fertilizers are broadcast evenly over the pond. Where benthic algae has become established, even pelleted fertilizers containing phosphorus may be broadcast directly. Ammonium sulfate or urea may be directly applied as these dissolve readily in water. It may be wise to dissolve superphosphate or triple-superphosphate, even pelleted ammonium phosphate and di-ammonium phosphate in water before they are applied. Regular side dressings have been observed to keep the algae growing. Weekly applications with small amounts is preferred. Where water exchange is done during spring tides, fertilizers are applied after the exchange operation is complete. Fertilizer applications are terminated 2 to 4 weeks before the ponds are harvested.
Once availability and desired quantity of natural food is assured either through watering (which brings in food into the pond and nutrients that would enhance growth of food in the pond itself) or through the use of fertilizers, stocking commences. Stocking densities vary with the species, the amount of food present, and availability of external feed in case natural feed is not sufficient, all other conditions in the pond being favourable for growth.
Thus for P. monodon rates can start from 2 000/ha for the extensive system, increasing to 4 000 or more in the semi-intensive system where fertilizers and supplementary feeds are used. In Ecuador, extensive systems use from 10 000 to 20 000 post larvae to P. vannamei and P. stylirostris per hectare. Where supplemental feeds are used, stocking rates go up to 50 000/ha. Recommendation for P. indicus in semi-intensive system using fertilizers only is 40 000/ha.
Ponds are filled during high tides but with pumps, filling can continue for as long as necessary and if good clean water is available. Water is allowed through screens to ward off entry of predators. Fine screens of 1/16" mesh are used during the first few weeks and as the shrimp grow bigger, wider mesh filters (1/8" to 1/4") take over. Entry of more water where the finer mesh screens are used could be accomplished by using bag nets instead of the conventional framed screens. The area through which water can pass would depend upon the dimension of the bag net.
In the extensive system, water is allowed as the tide would permit, partially drained just before the onset of the next high tide to be able to take in water again. The more exchange there is, the more probability that additional food has been brought in. Food brought in generally find browsing areas in substrates provided by left-over vegetation or aereal roots of the original mangrove trees, or some higher aquatic vegetation which have somehow started to grow.
In semi-intensive systems using fertilizers, water exchange is undertaken as above where conditions have become unfavourable (such as rise in salinity or abrupt lowering of salinity due to heavy rains or low oxygen content etc.) so as to conserve the fertilizers. However, a week after fertilizers are applied at low dosage, partial water exchange during spring tides can be safely done.
Where feeds are used either in supplementary or complete feeding, a regular water exchange routine should be undertaken to get rid of metabolites and provide oxygen expecially where there is high stocking. Systems using entirely formulated feeds or raw animal feeds (trash fish, clam shelle, etc.) would need a flow-through, with water exchange of from 3 to 10% or more per day.
Formulated feeds successfully used for shrimp have ingredients generally kept secret by the feed manufacturers even if they are required to indicate the formula in tags attached to the bags. Feed technologists and nutritionists, however, have drawn up a number of formulations on the basis of the both experiments and theories. One formula (see Table I) incorporates 14 ingredients and 4 supplements.
Artificial feeds are applied late in the afternoon and evenings when the shrimp become active. An intensive system farm in the Philippines feeds its P. monodon stock three times daily: 1700, 2200 and 0700.
Feed conversion depends on the feed efficiency and could range from 1.6 for good pelleted feed to 9 for clam meat.
Several diseases have been responsible for mortalities of shrimp in ponds. Black gill disease can be caused by accumulation of debris in gills, usually due to bad bottom conditions.
Fungus (Fusarium sp.) cause the gills to become black also.
Bacteria can also be responsible. Fungus also causes white shell disease where portions of the exoskeleton turn white. Several vibrio diseases have been reported as also those caused by virus. It is felt, however, that suceptibility to these epizootic diseases could be due results of stress particularly in systems where stocking rates are very high. Common complaints of shrimp farmers are soft shell, which could be a nutritional disease. Remedial measures have been found for some of these diseases, mainly involving dips in chemical solutions or use of antibiotics but where farming of shrimp is done in ponds, these are not easily applicable.
In Ecuador and in India, the harvesting of shrimp ponds is done mainly with the use of cast nets. In the Philippines, Indonesia and Thailand, the ponds are drained, the shrimp then collected in bag nets set to the gates, or in a catch basin from where they are seined out. Also in the Philippines, traps are set inside the farm and collection is done in the morning after water exchange during the provious evening had been undertaken. Shrimp are led to the trap by a leader that stretches from the dike to the no-return V opening of the trap.
Harvested shrimp are washed and chilled in iced water, then packed in ice for transport to the market or to packing centres where they are further prepared for shipment to far areas.
Some species can remain alive for hours (M. nonoceros and M. ensis) and in Japan where live shrimp has a very high price, P. japonious of marketable size are transferred to tanks where the water can be cooled gradually until they become lethargic, then packed in chilled sawdust.
The shrimp remain alive and reach Tokyo from the shrimp centres in the soouth even after 12 hours. Harvested shrimp sent to processing plants are frozen in blocks, head-on or head-off (tails only), peeled or deveined, and shipped to markets overseas.
ASEAN, 1978. Manual on pond culture of penaeid shrimp, Association of South east Asian Nations. National Coordinating Agency of the Philippines, 1978.
COOK, HL, 1976. Problems in shrimp culture in the South China Sea region SCSFDCP Publication No. SCS/76/WP/40, July 1976. 50p.
Duenas, J. et. al, 1983. Ponaeid shrimp pond culture in Ecuador. Proceedings of the first international biennial conference on Warm water aquaculture-Crustacea. Brigham Young University, Hawaii Campus, Laie, Hawaii, 9–11 February 1983.
Kungvankij, P., 1984. Over jaw of penaeid shrimp culture in Asia, November 1984. Network of Aquaculture Centres in Asia (FAO). ASA/WF/84/11.
Kungvankij, P., 1985. A prototype warm water shrimp hatchery, September 1985 NACA/WR/85/18. Technology Series No. 2.
Liao, I.C., and Chao, N.H., 1983. Development of prawn culture and its related studies in Taiwan. First international biennial conference on warm water aquaculture-Crustacea. Brigham Young University, Hawaii Campus, Laie, Hawaii, 9–11 February, 1983.
Liu, M.S., and Mancebo, V., 1983. Pond culture of Penaeus monodon in the Philippines: survival, growth and yield using commercially formulated feed. World Mariculture Society 14: 75–85 (1983).
Padlan, P. G. 1979. Pond culture of fish, shrimp and crabs in inter-tidal zones in the Far East. Coastal aquaculture: development perspective in Africa and case studies from other regions. CIFA/T9, FAO.
SCSFDCP., 1981. Report of the working on the biology and resources of penaeid shrimp in the South China Sea area part II. South China Sea Fisheries Development and Coordinating Programme (FAO) Publication No. SCS/CT/81/30 December, 1981.
SEAFDEC., 1984. Proceedings of the first international conference on the culture of penaeid prawns/shrimp, 1984. South East Asian Fisheries Development Center, Aquaculture Department Philippines.
Tacon, A. G. J., 1986. Larval shrimp feeding. ADCP/MR/86/23. FAO, Rome. 31pp.
Tang, Y. A., 1976. Planning, design and construction of a coastal fish farm FIR. AQ/Conf/76/E.68. ADCP, FAO, Rome.
Composition of Formula Diet for Penaeid Shrimp, Penaeus merguiensis and Penaeus monodon
|%||Protein||Lipid||Fibre||Ash||Nitrogen free extract|
|Meat and bone meal||10||42.5||(4.3)||20.4||(2.0)||6.0||(0.6)||7.3||(0.7)||23.8||(2.4)|
|Sesame cake meal, expellar||5||41.9||(2.1)||9.2||(0.5)||6.1||(0.3)||14.8||(0.7)||28.0||(1.4)|
|Groundnut meal, expellar||5||46.9||(2.3)||7.7||(0.4)||6.5||(0.3)||7.7||(0.4)||31.6||(1.6)|
|Rice bran (solvent extracted)||10||15.2||(1.5)||4.9||(0.5)||12.0||(1.2)||12.9||(1.3)||55.3||(5.5)|
Supplement: Cholesterol, 0.5; Soybean lecithin, 3; Corn or soybean oil,
4; Pollack liver oil, 4 Pellet size: 2 × 10 mm; Water: 30%
1 It is better to substitute wheat gluten M for Tapioca
Figure on bracket indicate % on formula diet.