WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2016 25 TOP AND BOTTOM. Variable cost, total return and gross margin of different treatments in 2012 and 2013 including labor cost. developed with consideration of crop rotation and suitable species compositions. A randomized complete block design was followed for distribution of treatments and replications within the experimental area. In control ponds, water depth was 50 cm and multiple stocking and selective harvesting continued throughout the year. In monoculture and polyculture treatments, pond water depth was 70-100 cm and production was divided into three crop cycles each year to allow for crop rotation in response to annual changes in salinity. In the control, ponds were stocked with Penaeus monodon, Metapenaeus monoceros, Chelon subviridis, Rhinomugil corsula and Oreochromis mossambicus at stocking densities of 2, 4, 0.25, 0.25 and 0.25/ m2, respectively, followed by stocking of Penaeus monodon in each month until September at 0.5/m2. Selective harvesting was carried out from April until the end of November. At the end of August, table-size Labeo rohita, Catla catla, Cyprinus carpio and Cirrhinus mrigala were stocked at 0.25/m2 for each species. In rotational monoculture in 2012, the first cycle was Penaeus monodon stocked at 3/m2 followed by monosex Nile tilapia Oreochromis niloticus at 4/m2 and Macrobrachium rosenbergii at 3/ m2. Based on observations of disease outbreaks and shrimp prices in local markets in 2013, the dry season was subdivided into two short cycles of shrimp with the goal of harvesting small shrimp by growing at relatively high density. So, Penaeus monodon were stocked at 5/m2 for 70 days in the first and second cycles followed by monosex Nile tilapia at 5/m2 from August to November. The rotational polyculture treatment was intended to keep a backup crop if shrimp disease occurred, thus reducing economic losses and also producing fish for local consumption. In 2013, ponds were stocked with Penaeus monodon at 3/m2 and monosex Nile tilapia at 2/m2 for 100 days followed by monosex Nile tilapia at 3/m2 and Mystus gulio at 2/m2 for 90 days. In the third cycle, Macrobrachium rosenbergii with Mystus gulio were stocked at Traditional aquaculture in Bangladesh is a century-old practice of growing shrimp and fish in coastal areas of the country. Favorable agroecology, very low investment and strong international market demand influenced quick expansion of shrimp monoculture in the coastal region. Although it became one of the key economic activities in coastal districts, it has been accompanied by positive and negative impacts. On one hand, it created a wide range of livelihood opportunities and on the other, it limited various ecological functions. In recent years, disease outbreaks have been recognized as the biggest obstacle to the development of shrimp aquaculture in Bangladesh, causing massive economic losses. In this context, collaborative field-based research is needed to evaluate ways to improve the saline aquaculture systems of Bangladesh. The CGIAR Research Program on Water and Food collaborated with farmers and conducted field-based research in high-salinity areas of southwestern Bangladesh between 2012 and 2013 to seek ways to make coastal brackishwater aquatic agricultural systems more productive, profitable, diversified and resilient. Experiments were designed, considering changes in saline regimes, to explore options to improve existing brackishwater aquaculture systems, with a focus on rotational monoculture and polyculture aquaculture farming systems to allow for crop rotation and risk reduction. The Experiments The study was carried out in the southern part of polder 3, one of the major shrimp farming areas, categorized as a highsalinity area. Three treatments — farmers’ existing practice (control), monoculture and polyculture — each with four replications were tested in 2012 and 2013. The control treatment was based on farmers’ current management practices, developed through three consultation meetings with more than 50 shrimp farmers in the southern part of polder 3. Monoculture and polyculture treatments were Improving the Productivity, Diversification and Resilience of Saline Aquaculture Systems in Coastal Southern Bangladesh K.A. Kabir, S.B. Saha, M. Karim, C.A. Meisner and M. Phillips (CONTINUED ON PAGE 26)
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