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close this bookLivelihood Options for Coastal Communities (IIRR, 1995, 77 p.)
close this folderWater-based activities
close this folderCapture fisheries
View the documentFish corrals
View the documentFish trap: Amatong
View the documentFish traps: Modified multipurpose fish trap
View the documentMilkfish-fry gathering
View the documentPrawn-fry gathering

Prawn-fry gathering

Most black tiger prawn or sugpo (Penaeus monodon) growers in the Philippines are concerned with the efficient production of marketable and good quality prawns from post-larvae (juvenile to sub-adult) in brackishwater fishponds.


Penaeus monodon

Majority of the prawn growers believe that efficient production with high survival, good growth and relatively disease-free prawn fry will come from the wild (not hatchery-bred). It is also preferred by most prawn growers and commands a higher price than the nursery-bred fry.

Natural seasonal occurrence of prawn fry is normally observed in areas with mangrove stands along brackishwater (15-27 ppt salinity) areas. Fry catching has generated seasonal income among the coastal people, especially children, unemployed youth and mothers who cannot brave the high seas for fishing.

Spawning and fry stage (post-larvae)

The life cycle of the crustacean prawn starts when the female attains sexual maturity at the age of 10-12 months when mating occurs during the molting of the female. The gravid (pregnant) prawns go to offshore areas of 20-70 m deep to lay their eggs. Two or three consecutive spawning can release half to one million eggs that can take place in one season.

The eggs hatch 12-15 hours after spawning. After 10-12 days and two more larval stages, they metamorphose into post-larvae which are similar to the adults. The post-larval stage occurs in brackishwater areas.

The adults remain in the sea (offshore) up to the old age of three to five years. However, some prawn species undergo spawning and stay in brackishwater without going to the open sea. Normally, the fry catching peak season is from September to February and May to June.

Methods of prawn-fry gathering

Most prawn-fry gathering municipalities still use the traditional method of fry catching—the hand net, push net (sagyap), fry sweeper and the fish corral type (tangab). Improved fry-catching technology not only increases catch that would otherwise be eaten by other fish species or lost, but also bigger income for fry gatherers.

An improved method of prawn-fry gathering is by placing several (5-20) bamboo torches (sulo) along seashores or near river mouths at night. Prawn fry is attracted by low-intensity moving lights. Fry catching can now be done during the night by using the fry sweeper.

Another improved method of catching prawn fry is with the installation of a series of bundled (tied) coastal grasses (dried or fresh) tied on long lines or rows of strings (plastic twine or No. 4 nylon rope). Place several sulo along the beaches or near river mouth and install several lines with bundled grasses tied to the lines at 40-50 cm distance of at least 20-30 m long. The rows or lines should be facing the sea. At night, the prawn fry are attracted by the sulo and, at the same time, cling to the substrates. Clinging to the materials (or bundled grasses of 5.08-7.62 cm diameter and 30.48 cm long) is an instinct of prawn fry for them to seek food source and as their shelter and sanctuary. Gathering of the fry is best done by using rectangular hand nets. Place the hand nets below the grass bundles, lift the grass line and shake the substrates so that the clinging fry will drop at the hand net. Fry gathering under this method can be done at dawn or daytime.


Prawn fry catching using the sulo and grass.

Prawn fry that are caught are placed in well-ventilated containers like pails, drums or wooden vats and kept in cool areas. Earthern jars or pots are used in bringing them to buying or concessionaire centers. Counting can be done by scooping the fry in the water.

Studies conducted in Western Batangas and Lubang Island (Occidental Mindoro) showed that higher catch by two to eight times is attained by using the improved method, using sulo and substrates versus the traditional ones.

Economics of production (prawn)

Assumptions


Stocking density

less than 50,000/10,000 sq m


Water management

tidal or pump


Aeration

no aeration


Fry source

wild


Feed use

natural supplementary


Dike construction

earthen


Crops/year

1-2


Harvest method

total harvest


Survival rate

60% or less


Production/cycle (kg.)

500 or less

Economics of production


Capital investment (per ha)




a. Pond development cost

P 30,000-50,000



b. Working capital

P 10,000-48,000


Total production cost per cycle

P 64,254.64



a. Direct cost

P 50,987.50



b. Indirect costs

P 13,167.14


Cost/kg output

1a 47.60


Net return per year

P 195,490.71


Return-on investment

1.09

An extensive system (stocks subsist on natural food grown with or without fertilization and pond water is changed through tidal exchange) of prawn culture requires a stocking density of less than 50,000/10,000 sq m and an investment requirement of P40,000-P98,000/10,000 sq m. With a survival rate of 60 percent, maximum annual production is approximately 1,000 kg. Annual production cost is P126,509.28 while net return is P195,490.71. Return on investment is 1.09 (Greenfields, Vol. 7, No. 1, January 1987).