It was more than a decade ago when Northern Mindanao’s prawn industry was almost crippled by Vibriosis, a luminous bacterial disease that caused sudden drops in the region’s shrimp production. The destruction caused by this event greatly affected the region’s shrimp producers prompting some intensive farms to close down, while extensive farms which contribute 88% of the region’s shrimps also suffered huge monetary losses.
In Region 10, Misamis Occidental alone has devoted 1,790 hectares of its total brackishwater fishpond area to prawn farming. Of this area, 95% are comprised of extensive farms which are characterized by low stocking densities of about 5 pcs /sq meter and below. These extensive farms are greatly preferred in this region since it is relatively cheaper to maintain but almost always produces high quality shrimp products because of less disease occurrences and problems. Likewise, extensive farming is more environment-friendly since it utilizes naturally available food organisms thus limiting the input of feeds and chemical supplements.
At present, prawn growers are using tilapia to increase the bloom of microalgae in greenwater ponds, which in turn, enhances the growth and survival of the cultured species, Several instances have shown that tilapia-treated ponds have more stable algal population, low luminous bacteria count and had lesser bacterial attacks.
These findings prompted the Bureau of Fisheries and Aquatic Resources in Region 10 to conduct a comprehensive study that will ultimately establish the role of tilapia in prawn culture as an agent for greenwater enhancement and in controlling Vibriosis.
Beneficial tilapia
Gigi Albor and Perlito Vallejos of BFAR region 10 conducted their study in Bonifacio, Misamis Occidental. The researchers stocked three ponds with 5 pc shrimp /sq meter without tilapia while another three ponds were stocked with the same density but with 5,000 pieces of tilapia in net cages. Prior to stocking , the researchers prepared the ponds by drying, liming, and pest eradication. Likewise the researchers fertilized the pond water with 2 bags/hectare of urea to ensure high plankton bloom. Growth, survival rates and profitability were computed and analysed at the end of the study.
Results showed that tilapia indeed contributes greatly to the survival of prawns. The survival rates of prawns in the three ponds with tilapia were relatively higher at 23.63%, 38.12% and 51.02% than those without at 5.7% , 11.05% and 7.97% . With these rates, the tilapia-treated ponds also had higher return of investment (ROI) rates at 126% , 181% and 251% respectively,as compare to the three ponds treated without tilapia that had ROIs of less than 50%
Likewise, researchers found that the water transparencies in ponds treated with tilapia are more stable than the untreated ponds, demonstrating that tilapia culture improved the growth and stability of certain microalgae which then inhibited the growth of pathogenic microbes that would otherwise have been fatal to the prawns.
Source: BAR TODAY, January- March issue 2002 by Thea Kristina M. Pabuayon
“greenwater treatment in enhancing the production of tiger prawn (Penaeus monodon fabricus) in extensive ponds” by Gigi albor and Perlito Vallejos, BFAR region 10 Cagayan De Oro city 2001