Cage culture of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) at different stocking densities in a shallow eutrophic lake Maria Lourdes A Cuvin-Aralar, Alma G Lazartigue & Emiliano VAralar Southeast Asian Fisheries Development Center, Aquaculture Department (SEAFDEC/AQD), Binangonan Freshwater Station, Binangonan, Rizal, Philippines Correspondence: M L A Cuvin-Aralar, Southeast Asian Fisheries Development Center, Aquaculture Department (SEAFDEC/AQD), Binangonan Freshwater Station, Binangonan,1940 Rizal, Philippines. E-mail: mlcaralar@aqd.seafdec.org.ph Abstract Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stock- ing densities: 10, 20, 30 and 40 shrimp m  2 . Another set of shrimp was stocked in concrete tanks as refer- ence samples at 30 shrimp m  2 . Signi¢cant di¡er- ences were observed among stocking densities throughout the 95-day culture. The ¢nal weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m  2 and reference tanks were observed respectively. There were no signi¢cant di¡er- ences in survival throughout the culture period, ran- ging between 69% and 77%. Daily growth rates (range: 0.11^0.24 g day  1 ) and speci¢c growth rates (range: 3.54^4.34%) also di¡ered signi¢cantly among stocking densities, both increasing with decreasing stocking density.The feed conversion ratio in the cages did not di¡er among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest fol- lowed the equation y 5 81.06x  0.54 ( R 2 50.938) and that of stocking density and production (in g m  2 ) is y 5 58.01 x  0.46 ( R 2 50.834). Keywords: Litopenaeus vannamei , freshwater, cage culture, stocking density, Laguna de Bay, Philippines Introduction The Paci¢c white shrimp Litopenaeus vannamei was recently introduced as a species in the Philippines. A few years ago, the National Fisheries Research and Development Institute (NFRDI) imported high health broodstock from accredited producers of Speci¢c Pathogen Free/Speci¢c Pathogen Resistant (SPF/ SPR) stocks for research purposes. It was only in Jan- uary 2007 that the government ban on the culture of this species was lifted in this country, backed by data obtained from the experimental trials and after a ser- ies of public consultations and hearings. The culture of this introduced species is rapidly expanding in the Philippines, primarily because of its short culture period due to its fast growth. Shrimp is traditionally cultured in coastal or estuarine environments. Recently, with the success of China and the US in the inland culture of shrimp, interest in their culture in low-salinity environments has grown. The species of choice for inland shrimp culture is the Paci¢c white shrimp L. vannamei be- cause it is a euryhaline species that can be found in 1^40 g L  1 salinity waters (Davis, Samochoa & Boyd 2004). A number of studies have looked into the ionic concentrations of low-salinity waters as a factor a¡ecting the growth and survival of L. vannamei in culture. Modi¢cations of the freshwater environment to di¡erent ionic concentrations of potassium and magnesium in 4 g L  1 salinity have been conducted (Davis, Saoud, McGraw & Rouse 2002; Davis, Boyd & Rouse 2005). These studies have shown that the sur- vival and growth of L. vannamei postlarvae are signif- icantly improved by the supplementation of potassium and magnesium in the culture waters. Successful acclimation of L. vannamei to 0.25 g L  1 has been carried out (Tomasso, Atwood & Browdy 2004). Aquaculture Research, 2009, 40, 181^187 doi: 10.1111/j.1365-2109.2008.02081.x r 2008 The Authors Journal Compilation r 2008 Blackwell Publishing Ltd 181