Study area and duration: The experiment was carried out at Dumurpota of Asasuni upazila in Satkhira district during the period from June 05, 2005 to December 05, 2005.
Experimental Ponds: A total of six ghers were taken for the study. Three of these ghers were stocked with all-male prawn and carp (AM1, AM2 and AM3) and the remaining three others were stocked with mixed sex prawn and carps (MS1, MS2 and MS3). Water area of AM1, AM2 and AM3 ghers was 0.49, 0.40 and 0.30 ha, respectively while that of MS1, MS2 and MS3 was 0.30, 0.45 and 0.61 ha, respectively.
Liming and fertilization: During gher preparation, liming was done after 7-10 days of ploughing with CaO at the rate of 125 kg ha-1. Cowdung, urea and TSP were applied at the rate of 500, 30 and 25kg ha-1, respectively. After fish stocking, cowdung, urea and TSP were applied once a month at the rate of 125, 15 and 10 kg ha-1, respectively.
Nursing of prawn PL: Prawn fry (PL 20) were collected from the local suppliers and stocked in all the rearing ponds at the stocking rate of 50,000 individuals ha-1. The rearing period was 45 days. After one and half month of rearing, male prawns were sorted out from the rearing ponds and stocked in the all-male ghers. The male prawns were sorted by observing their head. The head of male prawn was larger than that of the female.
Stocking: In both the culture systems, prawns PL were stocked at 10,000 individuals ha-1 and C. catla and L. rohita fingerlings were stocked each at a rate of 650 individuals ha-1 in all the ghers. The average initial weights of M. rosenbergii, L. rohita and C. catla stocked in AM1, AM2 and AM3 ghers were 7.33, 54.83 and 54.50 g respectively, whereas those in MS1, MS2 and MS3 ghers were 7.33, 55.07 and 54.17g, res.
Feeding: Feeding of post larvae (PL) was carried out from the following day of stocking in both the treatments. In the rearing ponds, rice bran and wheat flour were supplied at a rate of 7-10 kg ha-1 day-1. Subsequently, rice bran and wheat flour were supplied at 8-12 kg ha-1 day-1 for the first month followed by chopped snail meat only supplied at 25-37 kg ha-1 day-1 until harvesting.
Monitoring of water quality parameters: The five major water quality parameters (water temperature, water depth, dissolved oxygen, pH and salinity) of the experimental ghers were recorded fortnightly at 10-12 A.M. All the parameters were recorded by using a HACH water testing kit box (Model: FF-3, USA).
Growth and production monitoring: The growth (in terms of gain in weight) of prawn and carps were recorded fortnightly through random sampling. Weight of prawn was measured with a simple balance. The growth rate of prawn was calculated using the formula of Mahmud et al. (1993): Growth rate (g day-1) = W2 – W1/ T2 – T1. Where, W2 =Weight at time T2; W1 = Weight at time T1; T2 = Date of last sampling; T1 = Date of previous sampling