A new and better technology to culture shrimps is being used by many enterprising shrimp farmers nowadays. Green water technology is a technique that cultures shrimps in water that is abundant in phytoplankton i.e. Chlorella, turning the water green hence, its name.
In this system, tilapia is also grown in the reservoir or net cages/ pens in the ponds. The green water produced from tilapia helps control the growth of luminous bacteria that is bad for the growth of the shrimps.
The green water technology consists of: pond preparation, water culture/fertilization, stocking and stock sampling, feeding management, water management and aeration, and harvest and post-harvest handling.
Pond preparation
To prepare the pond, it should be dried and drained of water for three weeks until the soil at the bottom is cracked. The muck or the black soil at the bottom of the pond should be scraped off. Then the ponds are flooded with water and dried for another week. Hydrated lime at a rate of 2 tons per hectare is applied before the final flushing and sun drying.
When the pond is clean and dry, double hapa nets (10x10x1.5 meters) should be installed at the center of the pond. Bamboo catwalks from the dikes to the pens should be installed to facilitate easy feeding and monitoring of fish.
Water culture/fertilization
After installing the pens, the ponds should be filled with seawater to a maximum depth of 1.0-1.2 meters and the gates should be sealed. The water depth should be maintained by installing a depth gauge. To make sure that the water is free from predators and other possible competitors, teaseed powder (20 ppm) should be applied. Fine mesh screens should be installed at each outlet of the flume to prevent predators from entering the pond during pumping.
Stocking and stock sampling
To check the growth and condition of the shrimps, the stock should be sampled after 30 days from culture and every 10 days thereafter. For tilapia, stock sampling should be done monthly.
Feeding management
For shrimps, they should be fed right after stocking. Shrimp feeds are broadcasted around the pond with a portion of the feeding ration left in the feeding trays. Four trays measuring 0.25 square meter should be installed to monitor the amount of feeds consumed everyday. During the first 30 days, blind feeding is practiced. About 200 grams of feed per 10,000 postlarvae is given. One to three hours after feeding, the trays are lifted and the amount of feed consumed is estimated. From 40 days of culture, the shrimps are fed five times a day, i.e., 6:00 AM. 10:00 A.M., 2:00 P.M., 5:00 P.M. and 10:00 P.M. at 20%, 10%, 10%, 35%, and 25%, respectively of the total feeding ration.
Tilapia are fed 5% of the body weight. They are fed twice a day at 8:00AM and 2:00 PM and the ration is adjusted based on the average body weight of the fish every sampling period.
Water management and aeration
After 30 days of culture, 10-20% of the water in the pond is drained and replaced with water from the reservoir ponds. It should be noted that the water from the reservoir ponds should be allowed to stay for at least 4-5 days before they are used to replenish the water in the shrimp rearing ponds.
The ideal amount of dissolved oxygen is maintained by using six paddlewheel aerators. In the first 60 days, only four aerators are alternately operated for 24 hours. Another aerator is installed in each tilapia pen to increase the circulation of water and phytoplankton in and out of the pens.
Harvest and Postharvest handling
Shrimps are harvested when they weigh at least 30 grams. Harvesting is done by draining the water and collecting the shrimps using a harvest net installed at the pond gate. The collected shrimps are placed in water with crushed ice to maintain their quality. The shrimps are then sorted according to size and placed in boxes with crushed ice to be shipped to shrimp processing plants where they are packed for export purposes.
Source: “Green Water Technology” 2003 by Mr. Valeriano L. Corre, Jr. of the University of the Philippines in the Visayas, Miag-ao, Ilo-ilo
Article by Junelyn S. de la Rosa- bar.gov.ph, January-March 2004 Volume 6 No. 1
Photo: nis.gsmfc.org
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