Although shrimp farming has been developed for more than a century in Southeast Asia, the main farming operations are still traditional. Such operational practice is characterized by low yield and also relatively low technical and financial inputs. Due to high market demand of products and low acquisition cost of land, these traditional farms are still commercially profitable.
Shrimp yield in ponds can be increased by applying modern farming techniques such as intensification of culture operation through regularization of pond size, increase stocking density, employment of aeration, application of formulated feed, etc. This will mean a considerable increase in financial and high technology inputs which most small farmers in the developing countries may not be able to afford.
The ponds used in this type of farming system are generally irregular in shapes and sized (3–20 hectares). Usually each pond has a peripheral ditch 10–20 m wide and 30–60 cm deep. In Thailand, the middle portion of the pond is slightly elevated to about 40 cm above the bottom (Fig. 1), while in the Philippines, the pond bottom is entirely flat.
Extensive culture operation is considered the simplest culture approach. Seedstock normally come from the wild and supply is season dependent. Shrimp fry found in these farms either gained entrance during water exchange or are intentionally stocked by the farmer with fry collected from the wild. Extensive farming employs very low stocking densities, usually in the range of about 3,000–5,000 fry per hectare. In this grow-out scheme, supplementary feed is not given and water management is by tidal exchange.
Fig. 1. A typical shrimp pond layout in Thailand for extensive farming.
In Thailand, Indonesia and Malaysia, shrimp fry are allowed to enter the ponds through the pond gate which are open during rising tide. The gates are then closed as tide recedes. Trapped fry are allowed to grow inside the pond for two months before being harvested. In contrast, shrimp farmers in the Philippines do not rely on natural tidally introduced shrimp seeds but rather they stock their ponds (usually in polyculture with milkfish) with fry collection from the wild. The average stocking density ranges between 2,000 and 5,000 fry per hectare. In both farming approaches, production per unit area is very low.
In this farming method, the improvement over the traditional approach is in the introduction of a systematic pond configuration. The ponds are generally rectangular in shape with size about 1–3 hectares and water depth of 0.80 to 1.2 meters. Each pond has separate inlet and outlet gates to facilitate water exchange, pond preparation and harvesting. A diagonal ditch, 5–10 meters wide and 30–50 cm deep extending from inlet to outlet is also constructed to facilitate drainage of water and collection of shrimp during harvest (Fig. 2). The ditch also serves as a refuge for the shrimp during sunny day. This method involves higher stocking rates, use of supplementary feed and the implementation of a regular water management scheme. Current practices vary from country to country and within the country. The typical rate of stocking fry for semi-intensive culture operation varies from 20,000 to 50,000 fry per hectare. Supplementary feed, either formulated or fresh, is given daily in addition to the existing natural food produced through the application of fertilizers. This operation also requires the use of a water pump to facilitate water exchange.
While this approach would substantially increase yield per cropping, the use of supplemental feeds entails additional cost which generally accounts for the biggest share in operational expenditure.
The culture operation of the Amakusa type shrimp pen in Japan (Fig. 3) can be classified under this method of culture. The pen is an artificial enclosure constructed within shallow bays and intertidal zones for holding and raising shrimps. A rectangular or square vertical wall made of concrete is constructed to a height of 1 meter for holding water during low tide. A wooden frame with nylon netting is set on top of the concrete wall to prevent escape of shrimp and facilitate water exchange during high tide. This culture method takes advantage of the large body of water that is constantly being renewed through tidal fluctuations and by water current. The dimensions of the enclosure range from 2,000 m2 to 10,000 m2 with depth of 1.0–1.5 meters. Stocking rate ranges between 20–30 fry per m2. Average production is about 300– 400 g/m2 or about 3–4 tons/ha/year.
Fig. 2. A typical shrimp pond layout in Thailand for Semi-intensive farming.
Fig. 3. Amakusa type shrimp farm in Japan.
This culture operation is more sophisticated requiring very high financial and technical inputs. The rearing facilities are either earthen ponds or concrete tanks. The distinct features of this culture operation is the complete dependence on hatchery-bred fry, high stocking density, use of formulated feeds, application of aeration to increase dissolved oxygen level in pond water and intensive water management.
Sizes of pond or tank vary for 500 m2–5,000 m2 as found in Japan, Taiwan, Philippines and Thailand. Dikes may be of pure earthen material, earth coated with plastic sheets or concrete. Most designs include separate inlet and outlet gates or small water inlets for flow-through purposes. Drain out system is in the form of a centrally located drain pipe, a drain gate (sluice or monk type) or a combination of both (Fig. 4).
An excellent intensive method of culture operation for Kuruma shrimp developed by Shigueno has been widely practised in Japan. Culture facilities consist of circular tanks with capacities ranging from 1000 to 2000 tons and average height of 2 meters. A sand substrate covers the tank bottom and water circulation is effected by flow through system (Fig. 5). The shrimps are fed daily with high protein formulated diet. Stocking density ranges from 200–250 per m2 and average production ranges from 1.5 to 3 tons per crop in 1000 ton tank and about 10–20 tons/ha/year in earthen ponds with concrete dikes.