M. Begum
Bangladesh Fisheries Research Institute, Mymensingh 2201
M.A. Wahab
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh
M.S. Haq
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh
M.Y.Hossain
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh
M.M. Ali
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh
!so-nitrogenous fertilizer, Water quality, Fish production, Catla, Mrigal, Rohu
Bangladesh Agricultural University, Mymensingh
Animal Health and Management
The experiment was conducted for a period of 4 months from July to October'99 at the Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh. Nine earthen ponds with an area of 100m2 each and average maximum depth of 1.5 m were used for this study. Ponds were rain fed and well exposed to sunlight. Experimental design: The experimental ponds were randomly divided into three treatment groups for three levels of iso-nitrogenous fertilizers, viz., urea plus triple super phosphate (UT), cow manure (CM) and poultry-manure (PM) with three replications for each. The rate of urea and triple super phosphate for the treatment UT was fixed to the standard inorganic fertilization rate of 125 kg and 100 kg/ha per application, respectively, in Bangladesh aquaculture conditions. As the UT, i.e., 125 kg urea plus 100 kg triple super phosphate contains 56 kg N, the loading rates of CM and PM were calculated equivalent to 56 kg N as 7000 kg and 3500 kg/ha, respectively. The iso-nitrogenous fertilization rates were calculated on the basis of nitrogen content in respective fertilizers and manures. The total nitrogen content in poultry manure, cow manure and urea, used during the course of experiment, was analyzed (on oven dry basis) as 1.6%, 0.8% and 45%, respectively. Pond preparation, stocking and fertilization: Before starting the experiment, ponds were drained om, renovated and made free of any unwanted aquatic organisms. Lime (CaO) was applied at the rate of 250 kg/ha and left over for 5 days to sundry. After 5 days of liming, the ponds were filled up with underground water and fertilized with respective fertilizer at selective dosages. Seven days after fertilization, each pond was stocked with rohu (Labeo rohita), catla (Catla catla) and mrigal (Cirrhinus mrigala) at the rate of 10000 fingerlings/ha with the ratio of 1:1: 1. During the entire period of the experiment, fertilizers were applied twice in a month, while both CM and PM were applied into the ponds as slurry on wet basis and UT was diluted with water and sprayed over the pond water. Monitoring of water quality: Physicochemical parameters, viz.., temperature, transparency, dissolved oxygen (DO), pH, ammonia-nitrogen (NH4-N), nitrite-nitrogen (N02-N), nitrate-nitrogen (N03- N), phosphate-phosphorus (P04-P) and chlorophyH-a of each pond water were monitored at ten days interval between 09.00-10.00 hours. Temperature was measured by digital thermometer (precision = ±0.1°C) and DO by a digital DO meter (YSI model 58). Transparency was measured by a Secchi disc and pH by a digital pH meter. Analysis of NH4-N, N02-N, N03-N was done by using a HACH kit (model DREL 2000). Phosphate-phosphorus concentrations were determined by a spectrophotometer (Milton Roy Spectronic, model 1001 plus). Chlorophyll-a was determined spectrophotometrically at 664 nm and 750 nm of absorbance after acetone extraction. Plankton enumeration: Quantitative and qualitative samples of phytoplankton and zooplankton were taken fortnightly throughout the experimental period. To enumerate plankton population, 10 samples (5 liters of water in each sample) of water were collected from different areas and depths from each pond and were filtered through a fine mesh (25,u) plankton net. Then the filtered samples were taken in a measuring cylinder carefully and made up to a standard volume of 100 ml with distilled water. Samples were then preserved in small sealed plastic bottles containing 5% buffered formalin. Plankton were enumerated using a Sedgewick-Rafter counting cell (S-R cell). A 1ml sample was transferred to the counting chamber of the S-R cell (providing 10000 fields) and left to stand for 15 minutes to allow the plankton to settle. Using a binocular microscope (Swift M-4000), all cells/colony-forming units occurring in randomly selected 10 fields of the S-R cell were counted. Fish sampling and harvesting: Fish of each species (n> 10) from each pond we:re caught at each fortnight sampling day using a cast net. To determine growth gain, total length (em) and weight (g) of each fish were measured using a centimeter scale and an electronic balance (Ohaus model CT1 200). At the end of the experiment, the pond water was pumped out and all fish we:re harvested, measured and weighed. Weight gain per fish was calculated by deducting the average initial weight from the average final weight. Specific growth rate (SGR; %body weight/day) was estimated. Data analysis: For statistical analysis of data, a one-way ANOVA was carried out using STATGRAPHICS Version-7 statistical package for the PC.
Bangladesh J. Fish. Res., 8(1 ), 2004: 35-44
Journal