“The hatchery production of giant freshwater prawn (locally known as ulang) can be done by small-scale fishfarmers. Fishfarmers can utilize plastic drums (cut into half) as larval rearing tanks,” AQD scientist Dr. Maria Lourdes Aralar pointed out during the Farmers’ Forum on 11 July at AQD’s Tigbauan Main Station in Iloilo, Philippines. The plastic drum costs around Php 700 per piece and a drum can be converted into two 50-liter capacity larval rearing tanks. The stocking density for larval rearing is 50-100 larvae per liter and for nursery is 1,000 postlarvae per square meter. With a total hatchery area of 150 square meters, a farmer can have a net income of about Php 400,000 per run (estimated run per year is 4) with a postlarvae survival rate of 70% at 15 days.
Prawn grow-out culture also looks promising since fishfarmers can earn a net income of at least Php 100,000 per year for a total farm area of 5,000 square meters with 70% survival rate. The postlarvae are grown for four to five months with a stocking density of 10-15 pieces per square meter. The average harvest size of ulang is 25-35 grams.
The giant freshwater prawn exhibits aggressive behavior that may prevent culture in very high stocking densities. The provision of additional substrates to increase surface area improves production by reducing mortalities from cannibalism as well as increasing natural food production which can also be utilized by the prawns. The substrates may also provide shelter for moulting prawns which make them less vulnerable to aggression by other non-moulting prawns.
For the past two decades, the culture of giant freshwater prawn spread quickly as an alternative to shrimp culture due to the decline of the shrimp industry. From 1993-2002, the world production of giant freshwater prawn increased from 17,000 to 195,000 tons. In 2008, the Philippines made it to the top 15 producers of this species.
Dr. Aralar presented the prawn update during the Farmers’ forum on 11 July 2012 at AQD’s Iloilo station.