Zannatul FERDOUSHİ, Farhana HAQUE, Saleha KHAN, Mahfuzul HAQUE

The effects of two aquatic floating macrophytes (Lemna and Azolla) as biofilters of nitrogen and phosphate in fish ponds

Effects of different fish–edible floating aquatic macrophytes on water quality in aquaculture ponds through biofiltration of organic pollutants were studied for a period of four months from July to November 2001. Lemna sp. and Azolla sp. were used in treatment 1 and treatment 2, respectively. And treatment 3 remained as control. The stocking density of Rohu (Labeo rohita), Catla (Catla catla), Mrigal (Cirrhina mrigala), Thai sharpunti (Puntius gonionotus) and feeding regimes (rice bran and mustard oil) and fertilization rate were the same in all treatments. The values of dissolved oxygen, temperature, nitratenitrogen, phosphate-phosphorus, chlorophyll-a, alkalinity and plankton abundance varied among the treatments. It was observed that the lowest concentration of PO4-P (0.01 mg/L) and chlorophyll-a (26.99 μg/L) were found in treatment 1 and treatment 2 followed by treatment 3. This was probably due to the utilization of nutrients by the experimental aquatic macrophytes. Lowest concentration of NO3-N was found in treatment 2 during July, but the fortnightly average values of NO3-N were mostly found lower in treatment 1 followed by treatment 2 and treatment 3. The phytoplankton was composed of Euglenophyceae, Cyanophyceae, Bacillariophyceae and Chlorophyceae. Throughout the experimental period the dominant genus were Euglena, Anabeana and Microcystis. These macrophytes also appeared as a nutrient filter for absorption of nitrogen and phosphorus and removed the excessive amount of nutrients from the water body in treatments 1 and 2 and the aquatic environment remained in sustainable conditions.

Anahtar Kelimeler:

biyolojik kontrol, balık havuzu, su kalitesi, yerleşim sıklığı, filtrasyon, Azolla, Lemna, balık beslenmesi, balıkçılık, azot, fosfor

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