26 MARCH 2016 • WORLD AQUACULTURE • WWW.WAS.ORG 2/m2 for each. Like the monoculture treatment in 2013, the dry season was subdivided into two short cycles of shrimp where Penaeus monodon were stocked at 5/m2 for 70 days in the first and second cycles followed by monosex Nile tilapia at 3/m2. This was followed by Labeo rohita at 0.25/m2, Clarius bactracus at 1/m2 and Heteropneutes fossilis at 1/m2 from August to the end of November. No supplementary feeding was provided in control treatments. Partial supplementary feeding was given to shrimp and fish in both rotational monoculture and polyculture treatments. Data analysis was conducted using IBM SPSS Statistics 19. Local grass, bitter gourd, cucumber and the medicinal plant, neem Azadirachta indica, were planted on the gher dikes. Results System productivity. The experimental results from 2012 and 2013 clearly show that the annual yield from brackishwater aquaculture systems can be increased significantly by adopting improved management practices. Shifting from production focused on year-round shrimp culture to a season-specific annual production system increased fish production and furthermore, shrimp produced only in the dry season was greater than the annual production from control ponds (Table 1a and 1b). Together, with freshwater prawn in 2012 and shrimp alone in 2013, fish production was significantly greater than that of control ponds and total fish production was also significantly greater in both years than fish produced in control ponds. Suitable species combinations. Shrimp-tilapia in the dry season and carp-catfish (singh-magur) in the wet season resulted in significantly greater yields than other combinations. Farmers also ranked them higher during participatory evaluation following harvest. Cost-benefit analysis. Profitability was significantly greater with improved practices (i.e. monoculture and polyculture) than that using the farmers’ traditional practice (control) in 2012 and 2013. Profitability of the polyculture treatment was significantly greater than the monoculture treatment in 2012 (Fig. 1) and there was no significant difference in 2013. TABLE 1a. Shrimp and fish yields (kg/ha) of aquaculture crops by treatment in 2012. Culture patterns Cycle-1 Cycle-2 Cycle-3 Total annual yield Shrimp Tilapia Tilapia Tengra Prawn Tengra Shrimp Fish Farmers’ practice *210 728 Monoculture 198 - 2367 - 364 - 556 2367 Polyculture 173 1163 1520 352 232 287 404 3322 TABLE 1b. Shrimp and fish yields (kg/ha) of aquaculture crops by treatment in 2013. Culture patterns Cycle-1 Cycle-2 Cycle-3 Total annual yield Shrimp Tilapia Shrimp Tilapia Magur+singh Tilapia/rohu Shrimp Fish Farmers’ practice 390 659 Monoculture 566 - 292 - - *3308 857 3308 Polyculture 374 1744 193 778 558 **480 567 3560 FIGURE 1. Growing vegetables on pond dikes.
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