MD. ABDUL ALIM
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh
Prawn, Catla, Mola, Pond ecology, Production of fishes
Fisheries Field Laboratory, Bangladesh Agricultural University, Mymensingh
Farming System
Fish, Carp fish, Prawn
Study area and pond facilities: A 70-days experiment was conducted during 01 July to 10 September 2011 at the Fisheries Field Laboratory, Bangladesh Agricultural University, Mymensingh. Nine rectangular earthen ponds (all ponds are of 140 m2 each) and an average depth of 1.2 m each were used. Ponds were equal in size, depth, basin confirmation, bottom types and contour. The ponds were well exposed to sunlight, not interconnected by inlet and outlet and the main sources of water were rainfall and water supply from a deep tube well using a flexible plastic pipe whenever needed. The embankments were well protected and covered with grass. Surroundings of all ponds were fenced by 1 m high nylon net to prevent the entry of snakes and other predators, and escape of prawn. The water depth was maintained to a maximum of 1m. Experimental Design: The trial was conducted in a completely randomized design into three different treatments with three replications each. Stocking density of prawn (Macrobrachium rosenbergii) was same in treatments T2 and T3. The differences of three treatments were in the stocking density of mola. This is due to maintenance of same total biomass among treatments. In treatment T1, only mola was stocked at the rate of 272 dm-1. In treatment T2 the stocking density of mola was 83 dm-1 and in treatment T3, stocking density was 60 dm-1. In treatment T3, catla was added at the rate of 6 dm-1 to obtain same biomass. Feed for prawn was supplied in all treatments. Pre-stocking management: Pond Preparation All unwanted fishes were eradicated by drying the pond. Pond dikes were repaired using the excavated bottom soils. Ponds were manually cleaned of aquatic vegetation before starting the experiment. The weeds of embankment were also cleaned manually. Unwanted fishes and other aquatic organisms were eradicated. Lime was applied at 250 kg ha-1 (5 days after drying). The next day after liming, the ponds were filled with water from adjacent deep tube well. All ponds were fertilized with urea and triple super phosphate (TSP) at the rates of 50 kg ha-1 and dissolved in plastic buckets 10 to 12 hours before application. Then, urea and TSP were mixed together and applied into the ponds by spreading methods, equaling 70% of the pond surface area. After fertilization, the ponds were left 10 days to allow plankton development in water column. Surroundings of all ponds were fenced by 1 m height nylon net to prevent the entry of snakes and other predators, and escape of prawn from the ponds. Collection of prawn Juveniles: The PL of Prawn (Macrobrachium rosenbergii) was purchased from a commercial hatchery in Shomvugonj village of Mymensingh district. These PL and fry were brought to Fisheries Field Laboratory, Bangladesh Agricultural University, Mymensingh campus in plastic bags equipped with aerators. The fingerlings of catla and mola were collected from the ponds of Fisheries Field Laboratory, Bangladesh Agricultural University, Mymensingh district. Stocking: The juveniles of freshwater prawn (2.30), mola (1.50g) fry and catla (20.83g) fingerling were stocked according to the experimental design. The initial length and weight of each species were taken before stocking. Post stocking management: Diet formulation and preparation Feeds were prepared by using local pellet machine with following ingredients: Fish meal 15%, Mustard oil cake 20%, Soybean meal 20%, Rice bran 20%, Maize flour 20%, Molasses 4%, Vitamin-mineral premix 1%. Feeding: Formulated feeds were applied at 10% body weight at 1st month (up to 30 days) and reduced to 7% at 2nd month and were reduced to 3% up to the end of the experiment. Feed was distributed evenly over the ponds surface twice daily at 07:00 A.M. and 18:00 P.M. Individual weights of minimum 10% of initially stocked prawn in numbers were recorded monthly to estimate the biomass and adjust the feeding rate. The prawns were sampled using a seine net. Water quality monitoring: Throughout the experimental period, the water quality parameters were recorded weekly and monthly. Water quality measurement and sample collection were made between 07:00 to 10:00 A.M. on each sampling day. Transparency (cm), water temperature (oC), pH and dissolved oxygen (mgl-1) were measured every week at sunrise (07:00 A.M.) and sunset. Ammonia-nitrogen (mgl-1), Nitrate-nitrogen (mgl-1), Phosphate-phosphorous (mgl-1), Chlorophyll a (mgl-1) were measured monthly at Water Quality and Pond Dynamics Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh. Qualitative and quantitative study of plankton: From each 50 ml preserved sample, 1 ml sub-sample was examined using a Sedge wick-Rafter (S-R) cell and a binocular microscope (Swift, M-4000) with phase contrast facilities. The Sedge wick-Rafter counting cell is a special type of slide having a counting chamber which is 50 mm long, 20 mm wide and 1 mm deep; the volume of the chamber is 1 ml. The counting chamber is equally divided into 1000 fields, each having a volume of 0.001 ml. One ml sub-sample from each sample was transferred to the cell and then all planktonic organisms present in 10 squares of the cell chosen randomly were identified and counted. Taxa were identified to genus level. Sampling of fishes: Monthly sampling was done by using a seine net to observe the growth of prawn, mola and catla and to adjust the feeding rate. Small and rather inadequate sample 10-15 prawns were taken to make some rough assessment of growth trends, even knowing that such samples might not present the actual growth situation. Growth of prawn in each sampling was measured by using a digital electronic balance (Denver-XP-3000; precision=0.1 gm). General pond conditions and prawn health condition were monitored regularly during the culture period. The sampled prawns were handled very carefully as the species are very susceptible to handling stress. Harvesting: Fishes were completely harvested on 10 September after 70 days of rearing. Primarily, the partial harvesting of fishes was performed by repeated netting, using a seine net. Final harvesting was done by de-watering the ponds using pump. During harvesting all fishes of each pond were collected and weighed individually to assess the survival rate and pond production. Statistical analysis: For the statistical analysis of the data, a one-way ANOVA (Analysis of Variance) was done by using the SPSS (Statistical Package for Social Science) version-11.5. Significance was assigned at the 0.05% level.
MS Thesis, Examination Roll No. 11 FM. JJ-22 M, Registration No. 33697, Session: 2006-2007, Semester: January-June 2012; Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh
Thesis