The rearing of shrimps in the Philippines has been an old practice in brackishwater fishponds. The techniques of management, however, have been generally extensive. It was only after the development of shrimp hatchery operations which spilled out from Japan and Taiwan experience did intensification of shrimp farming come about. Approximately, 23 400 ha of brackishwater fishponds in the country have been converted to semi-intensive and intensive shrimp farming operations (IAC, 1989).
Expansion towards intensification of shrimp farming operations are also found in other ASEAN countries particularly in Thailand and Indonesia. This is boosted by government loans from the AsDB for shrimp farming development and technical assistance by government to the shrimp farming industry.
There are three different types of shrimp culture management systems in practice.
This type of shrimp farming operation is the traditional practice of natural seeding of ponds with shrimps by tidal inflow or pumping. Seeds may be stocked but of low density (3 000–5 000/ha); rearing of shrimps depends on natural food. Production level is, therefore, very low, ranging from 50–200 kg/ha/yr. In the Philippines where shrimps used to be grown as a secondary crop with milkfish, the production level ranges from 100–250 kg/ha/yr by natural seeding. However, if in addition to natural seeding, shrimp fry are stocked in the ponds, production level increases to 500 kg/ha/yr (Delmendo, 1970). Some farmers stock more shrimp fry than milkfish. It was reported that polyculture of shrimp and milkfish contribute to the control of insect larvae (Chironomid) population in fishponds (Apud, 1985). Extensive monoculture of shrimps is now commonly practiced. Stocking density ranges from 10 000 to 30 000/ha.
The traditional practice of trapping-growing operation used to be a common method in Malaysia, Thailand, Philippines, Indonesia and Vietnam, wherein seeding.is entirely dependent on tidal water inflow. A mixture of shrimps are accumulated in the ponds and allow them to grow on natural food. In Malaysia, periodic cropping every two months is carried out during an annual cycle as observed in Johor Bahru, Malaysia which showed a total production of 4 000 to over 5 000 kgs of shrimps which is high compared to average output of extensive pond operation in most ASEAN countries (Table 7). The species of shrimps harvested in trapping ponds include tiger shrimp, white shrimp, red shrimp, other shrimps of medium and small sizes.
Extensive pond operations could be shifted to semi-intensive management system. The main difference is the manner by which the ponds are prepared, seeded and the rearing regimen applied. Natural feeds are grown by application of inorganic and organic fertilizers; supplementary feeds are given to the shrimps during the culture period. Adequately prepared and well-managed ponds have high levels of production ranging from 2.5–7.0 tons/ha/yr or better (Rabanal, 1988). Compared with extensive management system, the ponds used for semi-intensive shrimp production are relatively smaller in area, 0.2–2.0 ha/pond (Wickins, 1986) and also deeper, 1.0–1.5 m (Rabanal, 1988). Stock density ranges from 50 000–100 000 PL/ha. One culture period may last from 100–150 days depending on availability of postlarvae.
Under semi-intensive operations, water exchange at the rate of 30–40 percent is effected either by pumping or gravity flow. Supplementary aeration is also used.
This system of shrimp pond management requires a good design of grow-out facilities. Pond units are much smaller, 0.1 to 1.0 ha but the depth could be the same as semi-intensive ponds, 1.0–1.5 m. The water exchange is continuous with at least 30 percent daily is necessary. Stock density ranges from 100 000 to 200 000 PL or more per ha per crop. It is possible to produce two crops per year with output levels of 5–12 tons/ha/yr (Rabanal, 1988). Artificial feeds, aeration and water exchange are imperative under this type of management.
Table 7. Production of a trapping pond, Johor Bahru, Malaysia
|Total||4 527||100.0||5 375||100.0||34 855||100.0||41 923||100.0|
|Tiger shrimp||50||1.1||128||2.4||1 002||2.9||2 178||5.2|
|White shrimp||1 120||24.7||1 231||22.9||18 727||53.7||19 935||47.6|
|Medium-sized shrimp||332||7.3||328||6.1||3 189||9.2||3 183||7.6|
|Small-sized shrimp||1 311||29.0||1 549||28.8||7 801||22.4||11 015||26.3|
|Red shrimp||1.714||37.9||2 139||39.8||4 135||11.9||5 612||13.4|
Source: Hirasawa, 1985
Table 8 shows some examples of shrimp production under different shrimp pond management systems in various countries.
A Philippine example of a water regime followed in intensive shrimp culture is as follows: (Stockwell and Williams, 1988).
No water exchange for the first 20–30 days after seeding; 5 percent daily water exchange from day 30–50; from day 50–75 water exchange increases to 7.5 percent daily, between day 75–90 water exchange increases to 10 percent daily; and from day 90 to just before harvest the rate of water exchange is 12.5 percent per day. The final water exchange may reach up to 100 percent which is undertaken about a week before harvest to induce molting. The hardening process is adequately completed in a period of one week after molting.
A qualitative and quantitative definition of shrimp culture management systems found in the Philippines is summarized below: (Young, 1987).
Table 8. Production examples from different types of prawn farm (data from various sources)
|Culture type and country||Stocking density (no./m-2)||Yield tonnes (ha-1/yr-1)||Crops (no./yr1)||Size of prawns (g)||Species|
|Panama||4–5||0.4 -0.9||1–3||20||P. stylirostris|
|Indonesia||1–5||< 0.2||1–2||P. indicus|
|Philippines1||1–3/two m2||0.05–0.5||1–2||P. monodon|
|USA, Hawaii||2–6||1.5–2||Continuous harvesting for 6 months||20–30|
|USA, S. Carolina||4–6||0.7–1.2||20–25||M. rosenbergii|
|USA, Hawaii||?||25–70||2.5||?||P. vannamei|
1 Delmendo, 1970
2 Rabanal, 1988
Source: Wickins, 1986