Seed Supply

Shrimp fry are generally collected from the wild. However, substantial number can be supplied through shrimp hatcheries.

7.1 Supply of post-larvae from wild stock

Natural abundant supply of naturally occuring post-larvae of Penaeid shrimp in many tropical/ subtropical Asian countries has supported a large number of shrimp farms in the region. About 80% of the small shrimp farmers still depend on wild fry for culture. Fry are collected either through trapping ponds or from natural fry grounds.

7.1.1 Trapping pond

Natural stocks of shrimp larvae are carried into brackishwater ponds by the rising tide when the pond gates are opened. When the tide starts to recede, the gates are closed and the shrimp seeds are thus trapped. The fry are allowed to grow for about two months before being harvested. Some progressive shrimp farmers use mechanical pumps to concentrate the number of larvae in the pond, hence, increasing the stocking density. A major problem faced by this practice is that many undesirable organisms also enter the pond with the shrimp fry.

Table 2. Comparison of Organic and Inorganic Fertilizers for use in Brackishwater Ponds.

ITEM	ORGANIC	INORGANIC
Concentration of N and P	Low. Average N ranges from 0.5% to 1.1% while P ranges from 0.1% to 0.4%.	High. For 18–46-0 fertilizer, it contains 18% N and 46% P or 35 times more than the organic fertilizer.
Composition of nutrients as N and P	Variable. N and P concentrations depend on diet composition given to the producing animal. Nutrients concentration diminishes through prolong storage or exposure to the elements.	Consistent.
Substrate for micro-benthos attachment	Does provide.	Does not provide.
Processing, storage and transport including application	High cost in terms of money, labor facilities and general unpleasantness is greater than inorganic fertilizers.	Low cost in terms of money, labor, facilities and minimal general unpleasantness.
Adverse effect on cultured stock	Mortality of stock commonly due to breakdown by microbial organisms leading to high BOD and low dissolved oxygen in the water.	Rare.
Growth factors	Present. Enhances algal production.	Absent.
Cost per unit of total N and P nutrients	Most expensive. Requires large amount to attain high N and P level.	Lest expensive since N and P are in concentrated amount. Application requires only smaller dose as compared to organic fertilizers.
Feeds for the cultured stock	Can be used directly such as rice bran and chicken manure especialy for species low in the food chain.	Cannot be consumed by aquatic animals.

7.1.2 Collection of wild fry

Many methods are employed in collecting shrimp fry. In the Philippines and Indonesia, shrimp fry are usually collected together with milkfish fry. However, due to increasing demand and high cost of fry, a number of efficient gears have been developed.

The various fry collecting devices currently being used include:

1. Twig - Small bunches of twigs are suspended close to or placed on the bottom of shallow lagoons, esturies and protected coasts. The shrimp fry are collected during low tide by placing a scoop net under each bunch of twighs as it is lifted up (Fig. 13).
2. Fry lure - Lure lines are made of saltwater grass. These are usually set along the banks of beaches and rivers (Fig. 14). Each line is 20 meters long and supported on both ends. Shrimp is collected as it is lifted up to the surface.
3. Scoop nets - In areas where there are abundance of aquatic weeds, a scoop net can be used to collect shrimp fry which usually cling to weeds (Fig. 15)
4. Push or scissor nets - The nets are with or without cod end. These are used along the beach, lagoons, bays, near shore and in estuaries which can be operated by hand or boat (Fig. 16).
5. Fry traps - This stationary gear consists of a wing and a collecting chamber. The cod-end of the collecting chamber is kept afloat by bamboo raft and the wing is fixed with bamboo poles against the incoming water (Fig. 17).

7.2 Seed from hatchery

Shrimp hatchery has become an important supply source for fry. Some hatcheries can produced shrimp fry all year round as long as spawners are available. An added advantage is that hatchery-bred fry of the same age are almost uniform in size and can be produced in large quantities at any one time. At 15–21 days old, the fry are ready for stocking in ponds. Although wild fry are ready for stocking in ponds. is inconsistent. The hatchery, therefore, is a more reliable seed source.

Fig. 14. Fry lure

Fig. 13. Twig

Fig. 15. Scoop net	Fig. 16. Push net or scissors net

Operation of scissors net.

Fig. 17. Fry trap

7.3 Transportation of fry

There are many ways to transport shrimp fry from hatchery or the wild to nursery or rearing ponds.

1. In fry tanks - Fry can be transported in plastic, fiberglass or canvass tanks at a density of 500–1000/liter with aeration (Fig. 18). Temperature of water can be lowered by means of ice in floating plastic bags.
   Shrimp fry at densities of 200–5000/ liter can be transported for 10 hours without heavy mortality.
2. Plastic bags - Very often, shrimp fry are transported in polyethelene bags with oxygen (Fig. 19). The bag (60×40 cm) is first filled with 6–8 liters of fresh seawater and then packed with 3000–5000 fry. The density may be reduced if the expected transport time is longer. After properly tightening the mouths of the bags, these are placed in styrofoam boxes or plastic buckets. Water temperature is reduced to about 22–25°C by crushed ice mixed with sawdust on the bottom, side and top of the styrofoam box. Under this condition, the fry may be kept alive for more than 12 hours during transportation.