giant freshwater prawnMacrobrachium rosenbergii is an indigenous species in the Philippines. It is locally known as ulang, udang, kising-kising, and pahe. Giant freshwater prawn has impressive growth performance and is able to survive and grow in turbid conditions. This species breed in saline water then move upstream from their spawning ground towards rivers, mountains streams and other bodies of water where they grow to a maximum size of more than 1 pound per piece. Ulang can be cultured in ponds, tanks, cages and rice paddies. In coastal areas, it can also be cultured in slightly saline environment, they can grow very well in 5 to 8 ppt. Ulang is a nocturnal animal. They are very active and feed very well at night. In ponds, they feed in shallow areas near the dike.

Culture System

Extensive – the stocking density is 1-3 pcs/sqm, stocks depend mainly on natural food produced through the use of organic and inorganic fertilizers and also on indigenous feeds.

Semi-intensive – the stocking density is 4-7 pcs/sqm, with combination of fertilizers and commercial feeds. To maintain good water quality, flushing/exchange of water must be done regularly depending on water quality appearance.

Intensive – the stocking density is 8-15 pcs/sqm, intensive feeding is needed, frequent water exchange is highly recommended, and with the use of aeration using paddle wheel to ensure enough supply of dissolved oxygen. Water quality parameters should be monitored regularly.

Site Selection

Water Supply – the site must be accessible to adequate water supply and free from contamination and pollution. Provide each compartment with an individual water inlet and drainage outlet.

Soil Characteristics – clay, clay loam, and sandy loam soils are best for fishpond projects. Deposits of organic matter of about 16% are best for fishponds. Avoid sandy, rocky or stony soils because these do not retain water in the pond.

Pond Compartments – area of grow-out ponds ranges from 1,000 to 100,000 sqm per compartment, smaller compartments are easier to manage however it requires higher cost for development.

Drainage – take into consideration easy drainage to facilitate harvest and proper cleaning of the pond bottom when constructing the pond.

Other factors to consider:

* Choose a flat terrain for easier excavation and leveling.
* Avoid exposing the fishpond to strong winds which generate wave action that destroys the sides of the dikes.
* Construct a diversion canal along the perimeter dike for runoff water during heavy downpour as protection from flood.
* Steep dike is preferred to prevent escape of stocks.

Fishpond Management

Pond Preparation

1. Total draining of fishpond – to eliminate old stocks, predators and unwanted species such as catfish, mudfish, biya, ayungin.

2. Pond poisoning – it is recommended to poison the pond, to be sure that all predators and unwanted species are eliminated. If ponds cannot be drained fully, poison is applied by spraying/ broadcasting it all over the pond bottom with at least 3 to 5 cm of water. Recommended poisons are tobacco dust, rotenone (tubli) at 25 kg per hectare or a combination of lime and 21-0-0 (5:1), mixed at 3g per liter. Use of chemical pesticides are not advised as it will have a residual effect on the pond and will also destroy soil quality.

3. Pond washing – pond washing is done to eliminate the effect of poison by letting filtered water come in and out of pond.

4. Leveling/ harrowing of pond bottom – the bottom of the pond is leveled to remove excess mud and dirt. It also facilitates harvesting especially during seining.

5. Sun drying of pond bottom – for old ponds, it is recommended to expose the pond bottom to sunlight and allow the soil to crack. Toxic gases evaporate and eliminates faster in a sun dried pond bottom.

6. Application of lime – if the pond becomes acidic, application of lime is recommended. The recommended rate is 100g/ sqm or 1,000kg /hectare. Soil samples can be submitted to the BSWM for analysis to determine acidity.

7. Screening of water inlet and outlet – before filling – in of water, fine mesh screen is installed in the water inlet to avoid entrance of unwanted species and at the water outlet to prevent of escape fish after stocking.

8. Installation of shelters – artificial shelters such as PVC pipes or recycled mineral bottles are placed in the nursery/ grow-out ponds as their hiding place during molting when their shells are soft as ulang are highly cannibalistic. Shelters should be a meter long and bound together (waist size) by GI wire or plastic cord. Arrange the shelters in the pond (20-30 pcs/ 1,000 sqm).

9. Filling in of water – pond is ready to be filled up with water to the favorable depth of 1.0 – 1.5 meters after screen is installed in the water inlets and outlets.

10. Basal fertilization – growth of natural food (plankton) in the pond is produced through basal fertilization. Organic fertilizer (chicken manure) is applied through broadcast method all over the pond at the rate of 1,000 – 2,000 kg/ha. In combination to chicken manure, inorganic fertilizer, 16-20-0 (Ammonium phosphate) is also applied at the rate of 100-200 kg/ha by hanging or platform method. This recommended rate may be increased or reduced depending on the amount of natural food already present in the pond. Basal fertilization should be done one week before stocking. Presence of natural food can be determined through change in color of water into green or yellow green. Over-fertilization should be avoided as it will cause plankton bloom which could result to oxygen depletion. Ammonium phosphate will do if chicken manure is not available.

11. Installation of hapa nets – install a 2x2x1m hapa net (5mm mesh size) one day prior to stocking of prawn PL. Situate the hapa net near the water inlet or at the deepest part of the pond. Fasten the net at stakes driven to the pond bottom. Place 2 to 4 coconut fronds inside the hapa to serve as shade and surface attachment for the PL. One unit of hapa can accommodate 2000 PL, survival rate is higher when stocking density per hapa is lower.

Transfer of post – larvae – contact the source of PL at least one week prior to purchase or transport , it is best to count the post larvae two days prior to hauling to lessen or avoid mortality.

Stocking of post larvae – it is best to stock PL 18 or bigger. However, it is not advisable to mix different age groups in one pond. Acclimatize the post larvae by letting the plastic bag container float on the pond surface for at least 15-20 minutes before releasing them in the hapa to prevent thermal shock that will cause mortality. When the difference in temperature between the bag and the pond is less than 5oC, the seeds can be released. Open the bag and carefully let pond water mix with the water bag. Continue the process until ulang starts to swim out of the bag. Only then that seeds are poured out to complete the stocking. Feeding of PL in the hapa is done five times a day. Commercial feeds with high protein content and right granule size is used. It might be desirable to pulverize feeds with big granule size. After a week in the hapa and observing normal feeding and other behaviors, lower the hapa to allow escape of PL into the pond.

Routinary Pond Activities

* Water level should be maintained at the average depth of 1 to 1.5 meter at all times. When the water is shallow, the prawns love to stay near shore and prone to predators like birds and snakes. Keeping the water deep at all times is therefore essential for the success of the project.

It is advisable to freshen water during the earlier months and change water (30% only) twice a month on the 3rd month and weekly on the last month.

* Weeding – regular cleaning of dikes is important to minimize lost of stocks due to preying by terrestrial animals. Dikes with thick vegetation are attractive to birds, snakes, frogs, lizards, rats, ducks and chicken. Fish predators such as mudfish and catfish can migrate over weedy dikes during cool and misty nights. It is also advisable to install scare crows or other similar devices to drive predatory birds away.

Desirable Ranges of Water Quality

a. pH level – 7.5 – 8.5
b. Hardness – 50 – 100 ppm
c. Temperature – 29 – 31oC
d. D.O – 5ppm
e. Ammonia – 0.1 – 0.2 mg/li
f. Alkalinity – 25 – 100 mg/li

Feeds and Feeding – M. rosenbergii are omnivorous. They can feed anything like zooplankton, algae, small mollusks and crustaceans and animal and vegetable organic materials. Ulang can be fed with commercial shrimp feed, tilapia feeds (sinking) as well as indigenous feeds such as kuhol, trash fish, boiled chicken and pig entrails, cow hide, cassava and vegetable and fruits refuse.

If at the early growing months of ulang, the amount of food given is insufficient, growth performance will significantly decline. Any attempt to recover from the loss will be futile even if greater amount of food is given in the latter part of culture.

Feeding Rate

Month Type Of Feed Feeding Rate Ideal weight of Stocks
1 – 15 Natural Food/ Com. Feeds    
16 – 31 Starter 2 10% of BW 2g
32 – 47 Starter 2 8% 4g
48 – 63 Starter 2 – 3 8% 6g
64 – 79 Starter 3 6% 10g
80 – 95 Grower 3 6% 12g
96 –  111 Grower 4 4% 15g
112 – 125 Grower 4 4% of BW 20g
126 – 139 Grower 4 2% of BW 24 – 30g
140 – 153 Grower 4 2% of BW 30 – 35g
154 – 167 Grower 4 2% of BW 35 – 40 g
168 – 180 Grower 4 2% of BW 40 – 50g

Feeding Schedule and Composition is as follows:

8 am – 25% – vegetable, fruits (squash, papaya, coconut, carrots etc)
2 pm – 30% – protein rich food (cooked kuhol, cow hide, chicken/pig entrails, biala, trash fish)
7 pm – 45% – commercial feeds

Determining Average Body Weight (ABW), Daily Feed Ration (DFR) & Feed Conversion Ratio (FCR)

1. Average Body Weight (ABW)

ABW (g)= Total weight of prawn randomly sampled/ No. of prawn sampled

2. Daily Feed Ration – this is the amount of feeds given daily

DFR = ABW x stocking density x feeding rate x survival rate

3. Total Feed Ration (TFR) – is the total amount of feeds given for the whole culture period

TFR = Daily Feed Ration x Feeding Duration

4. Feed Conversion Ratio (FCR)

FCR = Amount of feeds given during the culture period/ weight gain of prawn (kg)

Ex. Computation of daily feed ration (DFR) for 1,000 pcs PL.

1. ABW = 500g/ 40 pcs = 12.5g
2. DFR = 12.5g x 1,000 pcs x 6% x 70% = 367.5 g or 0.37 kg feeds daily

Side Dressing (regular fertilization) – there are two kinds of fertilizer available for use:

1. Inorganic fertilizers – this includes urea and 16-20-0 rate of application is 25kg/ ha/ wk through hanging method.
2. Organic fertilizers – most common is chicken manure. Application rate is 20 bags/ ha/ wk.

Methods of Harvesting

Selective harvesting – this is done after 5 months by partial harvesting, using seine nets. The seine net should be kept intact on the pond bottom to avoid escape of the prawn.

Total harvesting – seine first before the total draining the pond. Manual collection by hand is done with the remaining stocks in the pond bottom.

Record Keeping

Among the important data to be recorded are: daily pond activities, operating cost which includes pond inputs, quantity and cost (fertilizers, fingerlings, pesticides etc) production data, stocking, recovery and daily water parameters, ABW. Causes of failure and success can be traced from the records.

Source: DA- BFAR (Tuguegarao City)
Image credit: flickr

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