Effect of densities and culture systems on growth, survival, yield, and economic return of freshwater prawn, Macrobrachium rosenbergii, farming in the rice field in the Mekong Delta, Vietnam

Postlarvae of Macrobrachium rosenbergii (de Man 1879) were stocked at 2, 4, and 6 postlarvae (PL)/m² into rice fields under two culture systems, the integrated and the rotational prawn-rice system. Prawn was fed pellet feed twice daily. The growth of Macrobrachium rosenbergii decreased at higher stocking densities. Prawns in the rotational system grew faster than those in the integrated system. The yields ranged from 286±32 to 516±51, 412±17, to 584±41 kg/ha in the integrated and the rotational prawn-rice system, respectively. The yield at density of 2 PL/m² was significantly lowest (P <0.05) and was highest in the treatment. with 6 PL/m². However, at higher density, the investment cost significantly increased (P <0.05), while profit significantly decreased (P <0.05). At a density of 2 PL/m², cost benefit ratio and profit was the highest (P <0.05). The integrated rice-prawn system gives lower profits than the rotational system.