Improving the productivity of the rice-shrimp system in the south-west coastal region of Bangladesh.

Abstract

The production of wet-season rice (mid-August to mid-December) followed by dry-season (mid-December to mid-August) shrimp (Penaeus monodon) is a common farming system in the south-western coastal region of Bangladesh. Experiments were conducted in the farmers' fields during the rice- and shrimp-growing seasons of 2004, 2005 and 2006, with the aim of improving the total farm productivity of the rice-shrimp system through technological intervention. During the wet season of 2004, yield responses of different high-yielding (BR23, BRRI dhan 40 and 41, HR1 and 14) and traditional (Horkoz) rice varieties were evaluated for their responses to the prevailing salinity-influenced environment and integrated with: (i) GIFT (genetically improved farmed tilapia) strain of Nile tilapia (Oreochromis niloticus) alone; (ii) GIFT and giant freshwater prawn (Macrobrachium rosenbergii) at a 1:1 ratio; and (iii) prawn alone at a stocking density of 10,000/ha. In the 2005 rice season, the previous season's best-yielding rice varieties (BR23, BRRI dhan 40 and 41) were cultivated, integrated with a similar aquaculture species combination but at a reduced stocking density of 5000/ha. In the dry seasons of 2005 and 2006, the production of black tiger shrimp (P. monodon) was evaluated for three stocking patterns: (i) single stocking (5/m²); (ii) double stocking (3/m² followed by 2/m²); and (iii) double stocking (2/m² followed by 3/m²). Among the rice varieties, BR23 and BRRI dhan 40 performed best, with similar yields averaging about 5 t/ha. The reduced density of 5000/ha actually gave better fish and prawn yields, resulting in additional average production of 258 kg of GIFT and 71 kg of prawn/ha. The net return from GIFT alone was Tk10,858/ha and that from prawn was marginal or negative. Single and double stocking of shrimp did not show any significant differences in body weight, survival rate and yield, with the values ranging from 20 to 24 g, 26 to 35% and 289 to 380 kg/ha, respectively. There were considerable variations in survival and production within each treatment, particularly because of higher shrimp mortality in the replicate ponds that had comparatively shallower water depth during the culture period. Single stocking resulted in average net returns as high as Tk67,500/ha and was considered more suitable in rotation with rice.