M. S. R. Khan
Department of Marine Bioresources Science, Chittagong Veterinary and Animal Sciences University, Chittagong 4225
M. M. Khan*
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh
N. Akter
Department of Fisheries Management Bangladesh Agricultural University, Mymensingh-2202, Bangladesh
M. A. Wahab
Department of Fisheries Management Bangladesh Agricultural University, Mymensingh-2202, Bangladesh
Chitralada, GIFT tilapia, Strain, Freshwater prawn, Polyculture
Fisheries Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh
Animal Health and Management
Experimental design and site The experiment was conducted in a completely randomized design into 3 treatments with 3 replications of each in 9 earthen ponds (80 m2 each) at the Fisheries Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh for a period of 120 days from mid April to mid August 2009. Only prawn, prawn with GIFT and Prawn with Chitralada were stocked as treatment T1, T2 and T3, respectively. Stocking density of prawn was 30,000 h-1 and tilapia as 10,000 h-1 in all treatments. The ponds were fenced by fine meshed synthetic net to protect rodents and escaping of prawn. The water depth was maintained around 1 m, and two palm leaves were used as shelter of prawn juveniles in each pond. Pond Preparation and stocking All undesirable fishes were completely eradicated by drying of the ponds and aquatic weeds were removed manually. Lime (CaCO3) was applied at a rate of 250 kg ha-1 and fertilized 3 days after liming with urea and triple super phosphate (TSP) each at a rate of 25 kg ha-1 after three days of liming. The juvenile of M. rosenbergii (0.715 g) were collected from Bangladesh Fisheries Research Institute, Mymensingh. Prawn juveniles were brought to the experimental site using plastic tanks equipped with aerators. The fry of Chitralada (0.90 g) were collected from a local hatchery at Kasinathpur, Pabna district and GIFT fry (0.89 g) were collected from local hatchery Agro-3 at Mymensingh district. In order to ensure the same age, fry of the same hatching date was collected and was transported to the experimental site through well-oxygenated air tight plastic bag. Post stocking management Floating feed for tilapia was provided 5 minutes before giving the sinking feed for prawn. Both were fed with pelleted feed containing 28% crude protein, daily at a rate of 10% of body weight for 1st month, 8% for 2nd month, 6% for the 3rd month and 5% of body weight for rest of the cultured period. Half of the required ration for a day was supplied in the morning and rest half in the evening. Feed requirement were calculated and adjusted after each sampling of prawn once in a month. Water quality monitoring The transparency of water was measured by a Secchi disc of 20 cm diameter. Water temperature and dissolved oxygen was recorded by digital dissolved oxygen (DO) meter (YSI MODEL 58). pH was measured by a direct reading pH meter (HACH) at the pond site. Plastic bottles with stopper having a volume of 250 ml each and marked with pond number were used for collection of water samples. Water samples were collected by using a sampler designed in a manner that it was representative to all layers of the water column (vertical haul of the tube sampler covering about 1 m depth). Then the samples were transferred to the laboratory and 100 mL of water from each bottle was filtered through a glass microfibre filter paper (Whatman GF/C) with the help of an electric air pump for nutrient and chlorophyll-α analyses. Total alkalinity was determined using the titrimetric method. Chlorophyll-α was determined using a spectrophotometer (Milton Roy Spectronic, Model 1001 plus, Rochester, NY, USA) after acetone extraction (Boyd, 1982). Nutrient analyses were performed using a HACH kit (model DR 2010, HACH, Loveland, CO, USA a direct reading spectrophotometer). Total alkalinity was determined by acid titration following Stirling (1985). For plankton samples, ten litres of water was sampled monthly from five different locations of each pond and filtered through a 25 mm meshed plankton net. Each filtered sample was transferred to a measuring cylinder and made up to a standard volume of 50 mL with distilled water and buffered formalin (10%), and preserved in a sealed plastic bottle until analysis. Plankton was counted using a Sedgewick Rafter counting cell (S-R cell) under a binocular microscope (Olympus, M-4000D, Tokyo, Japan) following Stirling (1985). The quantitative estimation of plankton was done using the following (Stirling, 1985) equation:
N= (A ×1000 × C)/ (V× F × L) Where, N= Number of plankton cells or units per liter of water, A=Total number of plankton counted, C= Volume of final concentrate of the sample in ml, V= Area of field (mm2), F= Number of fields counted, L= Volume of original water in liter.
Tilapia and freshwater prawn was sampled monthly using seine net to assess their growth and health condition. At least 10 prawns from each pond were taken to make assessment of growth trends and to readjust feeding rate. Length and weight of prawn and sampled fish were measured using a measuring scale and digital electronic balance (OHAUS, MODEL No. CT-1200-S). Prawn and tilapia were handled carefully to avoid stress during sampling. Final harvesting of prawn and tilapia fish At 120th day of stocking, water was pumped out from the ponds and all prawns and tilapias were harvested, weighed by an electronic balance and measured by a measuring scale. Weight gain per fish was calculated by deducting the average initial weight from the average final weight. The net production of each species was calculated by deducting stocked biomass from gross production (harvested biomass). Specific growth rate (SGR) was estimated as: SGR = [Ln (final weight)-Ln (initial weight)] X 100 / culture period (days). Survival rate of prawn and fish was calculated by the following formula: Survival (%) = (No. of harvested individual/ No. of stocked individual) × 100. Statistical analysis For the statistical analysis, significant variation among the means of the treatments were compared and determined through descriptive one-way analysis of variance (ANOVA) using the SPSS (Statistical Package for Social Science, version-16.0) and post-hoc analysis was done by Duncan Test. Independent two tailed t-test was performed to analyze the growth and production performance of tilapia. Significance was assigned at 0.05% level.
J. Bangladesh Agril. Univ. 14(1): 127–134, 2016 ISSN 1810-3030
Journal