The culture of giant freshwater prawn, Macrobrachium rosenbergii, had been suffering setbacks due to insufficient supply of quality post-larvae. As early as early 80’s, the municipality of Calumpit In Bulacan pioneered a hatchery but failed to produce post-larvae. Calumpit, is known for the giant freshwater prawn popularly known as “ulang”. In fact, the species is proudly engraved in the municipality’s emblem.
Recently, the giant freshwater prawn which thrives in the rivers of Pampanga and Bulacan was identified by the National Fisheries Research and Development Institute as Macrobrachium rosenbergii rosenbergii. It grows comparably to the Thailand strain, Macrobrachium rosenbergii dacqueti. The local strain differs with the Thailand strain only in color. The Thailand strain is known for its bluish color while the local strain is transparent. Juveniles of these two strains are available in Pampanga and Bustos River during dry season.
Tilapia, on the other hand, remains the Region’s primary aquaculture crop. Region III is undisputedly the country’s number one producer of tilapia. To further maximize the utilization of tilapia ponds In the region, the Bureau of Fisheries and Aquatic Resources-Regional Office No. Ill conducted a Techno-Demo Project on the Polyculture of Tilapia and Ulang in Lahar-Affected areas. Initial results prove to be promising. Survival in ponds reaches as high as 70%.
1. Drain and tun dry.
Drain and dry the pond completely. Dry for about a week or more, depending upon the weather, until the bottom cracks or harden sufficiently to support a man on his feet without sinking more than 1 cm.
2. Cultivate and level pond bottom.
Till or cultivate the pond bottom as soon as it is drained. Do this by stirring or cultivating with a shovel, rake, or rotavator. Level the pond bottom after it is cultivated. Leveling makes the pond bottom slope gradually from its farthest end down towards the drainage structures- the deepest portion of the pond.
3. Repair gates, screens and dikes.
Check all gates and pipes for broken slabs and other parts. Repair screens to prevent predators and pests from entering the pond system. Clean to remove debris, which may cause clogging. Check all dikes for leakages and seepages. All dikes must be watertight.
4. Pest and predator control.
Pests and predators can be eliminated through applying hydrated lime (250 kg/ha) and ammonium sulfate (50 kg/ha) If the pond cannot be totally drained. Hydrated lime increases the pH level of pond water. Ammonium sulfate will be applied 10 minutes after hydrated lime. Hydrated lime and ammonium sulfate should be both applied in dissolved form. This process will release ammonia (NH3) gas which further suffocate and kill unwanted species. Predators can be avoided by proper leveling of the pond bottom, avoiding shallow areas. Always keep banks and dikes clean to prevent snakes from harboring in the ponds which is also a threat to the species to be cultured.
Condition Soil by Leaching and Liming
1. Leaching (Washing). Wash or flush the pond bottom to reduce acidity. This process is effective in slightly acidic soil. Pond bottom must be sloping (at least 2%) towards the drain gate.
2. Liming. Apply lime in fishponds primarily as a soil conditioner. Liming corrects soli acidity. Broadcast or spread the needed lime over the drained pond bottom. Mix the lime thoroughly with soil to attain maximum effectiveness. Lime is applied at 1000kg/ha.
The use of chicken manure is discouraged due to possible presence of antibiotics. Instead, the use of probiotics and inorganic fertilizer is recommended.
1. Platform Method. Apply inorganic fertilizers in fishponds using the platform method. The platform is a table like structure about 75 m2 positioned with its surface horizontal beneath the water surface. Position the platform 15- 20 cm below the water surface. Do not place this in corners, or in areas shielded from the wind.
2. Teabag Method. Put the inorganic fertilizers by placing them in gunnysacks suspended in the water to enable the fertilizer to dissolve gradually thus, providing a continuous supply of nutrients for the plankton. This method is used for the side dressing or weekly fertilization. Do not apply fertilizers during inclement weather conditions. Fertilizers are not effective without sunlight.
Installation of Artificial shelters. Artificial shelters made from bundled bamboo twigs or suspended nets attached with sinkers are installed in ponds with a distance of at least 2 meters by two meters. These shelters serve as refuge during molting when they become vulnerable to attacks from non-molting uiang.
Installation of feeding trays for ulang juvenile. It is recommended to use feeding trays for ulang fry/juvenile which are being fed during night time. Feeding trays measuring 0.5 x 0.5 meters made from fine mesh net and bamboo, weighed down by sinkers are also recommended.
Stocking of Fingerlings and Post-Larvae
The best time for stocking fingerlings in the pond is late afternoon or early morning. Before the fingerlings are released, ensure even temperature between the water in the plastic bags and the pond where these are to be stocked, introduce water gradually from the pond to the plastic bags until the temperature is almost the same.
Ulang post-larvae, preferably PL 15, are stocked one month ahead of tilapia fingerlings at the rate of 3 PL per square meter while tilapia fingerlings, preferably size 22 (0.5 grams) are stocked at 3 pieces per square meter.
To stock, bring the plastic bag of fingerling to the pond preferably near the gate, which is, supposed to be the deepest part of the pond: Bring down each bag to the pond and tilt toward one end to allow the pond water to flow gently into the bag. Allow the fingerlings to swim out of the bag voluntarily.
Prepared By: Wllfredo M. Cruz, OlC-Center Chief, Research Outreach Station for Freshwater Development Looc, Castillejos, Zambales