2.1 Study area and pond facilities The experiment was carried out at Fulpur, Tarakanda, Gafforgaon, and Nandail Upazilla under the Mymensingh district from January to June through a participatory approach. The sites were selected considering the potential of prawn polyculture with carps.
2.2 Experimental ponds The experiment was conducted in 12 perennial farm ponds. The culture system was assigned to four treatments in four Upazila having three replications each.
2.3 Pond preparation Unwanted fish were removed by netting followed by using rotenone @ 35 gdec.-1 . After three days of using rotenone, lime was applied @ 1 kgdec-1. After three days of liming, the ponds were filled with deep tube-well water to maintain required water depth. After three days of watering, all the ponds were fertilized with cow dung, urea, and TSP @ 6 kgdec-1, 100 gdec-1, and 200 gdec-1, respectively.
2.4 Juveniles and Fingerlings Stocking The experimental ponds were stocked with uniform-sized, overwintered juveniles of Macrobrachium rosenbergii and fingerlings of Labeo rohita, Catla catla, Hypophthalmichthys molitrix, and Ctenopharyngodon idella for all treatments. The stocking density of M. rosenbergii, L. rohita, C. catla, H. molitrix, and C. idella was maintained in all the treatments at 40, 4, 4, 10, and 2 dec-1 , respectively.
3.2 Production of prawn and carps The production of prawn and carps differed significantly throughout different treatments (Table 2). The total production of giant freshwater prawn in Fulpur, Tarakanda, Goffargaon, and Nandail was 638.38, 629.66, 592.23, and 558.59 kgha-1 , respectively, and finfish production was 1702.52, 1634.59, 1900.93, and 1917.49 kgha-1 , in that order. The significantly highest prawn production was found in Fulpur upazilla (638.38 kgha-1) and the lowest was in Nandail upazilla (558.29 kgha-1), while the total production of carps was the highest in Nandail upazilla (1917.49 kgha-1) and lowest in Tarakanda (1634.59 kgha-1). Mondal et al. (2005) reported average prawn yields of 481.50, 433.50, 402.25, dec-1 for calcareous supplement.
2.6 Water quality monitoring The water quality parameters such as water temperature, water transparency, depth, dissolved oxygen, and pH were recorded fortnightly between 8 and 10 a.m. All parameters were recorded using a commercial kit box (HACH FF-1, USA). Secchidisk was used to assess water transparency.
2.8 Survival rate The survival rate of the total stocked prawn and fish were calculated as total catch of fish at harvest divided by initial release of fish and converted to percentage.
2.9 Statistical Analysis The results are presented here as mean± standard error. Oneway analysis of variance (ANOVA) has been tested, and Tukey’s honestly significance difference (HSD) process has been applied for comparing different treatments at the 95% confidence level.