Momtaz Begum
BFRI, Brackish Water Station, Paikgacha, Khulna - 9280, Bangladesh
Md. Yeamin Hossain
Laboratory of Aquatic Resource Science, Faculty of Fisheries, Kagoshima University, 4-50-20 Shirmoarata, Kagoshima, Japan; Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi -6205, Bangladesh
Md. Abdul Wahab
Zoarder Faruque Ahmed
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh, Bangladesh
Md. Jahangir Alam
BFRI, Brackish Water Station, Paikgacha, Khulna - 9280, Bangladesh
Md. Mahfuzur Rahman Shah
BFRI, Brackish Water Station, Paikgacha, Khulna - 9280, Bangladesh
Saleha Jasmine
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi -6205, Bangladesh
Fertilizers, Iso-nutrients, Phytoplankton, Zooplankton, Earthen ponds, Bangladesh
Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh
Crop-Soil-Water Management
Ponds description and design of experiment: The experiment was carried out for a period of eight weeks in six earthen ponds situated at the Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh, Bangladesh. Rectangular shaped ponds, of 100 m2 each, with average depths of about 1.5 m, well exposed to sunlight and free from aquatic vegetation were used. The pond were initially dried out, pond bottom was ploughed and kept exposed to sunlight for three days. Then ponds were further treated with lime at the rate of 250 kg ha-1 and filled-up with underground water up to a depth of 1 m. The commonly used fertilizer combinations of cow manure, urea and TSP at the rate 5000, 125 and 100 kg ha-1, respectively, was applied for treatment-1 (T-1). This combination contained approximately 102 kg N and 65 kg P. Another combination of poultry-manure, urea and TSP at the rate of 2000, 125 and 100 kg ha-1, respectively, was used for treatment-2 (T-2) and the application rate of poultry manure was adjusted to make the nutrient (N and P) content of fertilizer combination in T-2 similar to that in T-1. The nutrient contents of manure and inorganic fertilizers (Das and Jana, 1996) were used to calculate the amount of cow and poultry manure in making up a similar rate nutrient application. Experimental ponds were randomly selected for two fertilizer treatments with three replicates for each. Fertilization of ponds was started on the 5th day after liming and filling of the ponds and the same applications repeated fortnightly for the entire period of the study.
Plankton analysis
Collection of plankton samples: Sampling for plankton was done on a weekly basis from each of the experimental ponds using a column sampler. Two litre water samples were taken from different points and depths using the flexible and uniform plastic tube sampler (diameter 8 cm) and the samples properly labeled in plastic jars.
Preservation of plankton sample: The samples were fixed with 2 mL of Lugol’s iodine (1:1000) for sedimentation and preservation of the plankton, pending laboratory analysis followed by settling for 2 to 3 days. The supernatant from the sedimentation was then carefully siphoned out and the volume made up to 50 mL. The concentrated samples were then preserved into small, properly labeled and sealed plastic bottles for microscopy counts.
Enumeration and identification of plankton: The concentrated preserved plankton samples were analysed on a Sedgewick-Rafter counting cell (SR-cell) under a compound binocular microscope (SWIFT M 4000-D). From each sample, 1 mL sub-sample was transferred to the cell and all planktonic organisms 10 randomly selected squares of the cell enumerated. The plankton abundance in the original volume was then computed:
| Where, |
| N |
= |
Number of plankton cells or units per liter of original; |
| A |
= |
Total number of plankton counted; |
| C |
= |
Volume of final concentrate of the samples in mL; |
| V |
= |
Volume of a field in cubic mm; |
| F |
= |
Number of fields countednd |
| L |
= |
Volume of original water in liter. |
This was repeated for all the pond samples and the plankton density in each pond expressed as the means of the pond samples in Number of plankton cells per liter of water (No.s/L). The plankters were further identified up to genus level following the standard methods.
Statistical analysis: Data were analyzed for one-way ANOVA and any differences at 5% level of significance were noted using the statistical package, Statgraphics Version 7. Graphs were done using Microsoft Excel ®, 2002.
Pakistan Journal of Biological Sciences, 10: 1221-1228; ISSN 1028-8880
Journal