ABUNDANCE AND SEASONAL VARIATION OF PLANKTONIC COMMUNITY STRUCTURE IN THE RAMSAGAR LAKE, DINAJPUR, BANGLADESH

Abstract

An experiment was conducted on Abundance and seasonal variation of plankton community structure in the Ramsagar Lake, Dinajpur, Bangladesh for a period of one year (January 2017 to December 2017). After two months pre-sampling three sampling sites were selected on the basis availability of plankton. Samples were collected monthly from three sites with three replication for each. Water quality parameters namely, temperature, p H , dissolved oxygen and transparency were measured at monthly intervals. All water quality parameters showed significant difference (P<0.05) among different seasons. During the study period the air temperature of water range found from 18.23 to 35.820C among the seasons. Air temperature highest mean value found in Autumn (33.33±3.99) and lower in the winter (24.45±3.99). The water temperature ranged varied 20.03 to 34.89 0C. Water temperature mean value was found higher in Autumn (31.66±1.89) and lower in the Spring (22.23±2.17) season. Water transparency range was varied from 28.50 to 54.43 cm in the experimental lake. The highest mean value of transparency was found in the Autumn season (47.52±4.37) cm and the lowest value was in Spring (36.91±6.53) cm. The dissolved oxygen concentrations under various treatments were found to fluctuate from 5.25 to 8.67 mg/l. The highest mean value of dissolved oxygen concentration was found in winter season (8.01±0.42) and the lowest value was observed in spring season (6.98±1.06). The pH values ranged varied from 6.25 to 8.00. An average ranged p H was found during the study period. The highest mean value of pH was found in spring season (7.51±0.27) and the lowest value of pH was found in Autumn (6.85±0.25). All parameters are suitable for growth and reproduction of fish and the fish culture. The qualitative and quantitative study of plankton was carried out at the laboratory of Fisheries Management, Faculty of Fisheries, HSTU by using microscope. A diversity of plankton was found in Ramsagar lake. In total 4 groups and 31 genera of phytoplankton were observed in the lake among them Chlorophyceae was the dominant group of phytoplankton. 15 genera of Chlorophyceae, 8 genera of Bacillariophyceae, 7 genera of Cyanophyceae and one genera of Euglenophyceae were found during the study period. Phytoplankton abundance showed significant difference (P<0.05) among different seasons. The highest phytoplankton was observed in summer season and the lowest observed in winter. In terms of month the highest phytoplankton was observed in June-July and the lowest observed in December- January. On the other hand 4 groups and 7 genera of zooplankton were found during the study period. Among the genera of Rotifera, 2 genera of Copepoda, one genera of Cladocera and one genera of crustacean were found. Rotifera was the dominant group among the zooplankton. Seasonal variation of total zooplankton was found in the study. Zooplankton abundance showed significant difference (P<0.05) among different seasons. Considering all the facts the total plankton production was found highest in summer season and the mean values were (9.78±1.70) and lowest in winter season and the mean values were (8.09±1.62). Seasonal variation of plankton abundance was found throughout the year. It might be suggest that Ramsagar is a water resource with a diversity of plankton which is an important primary producer and important for fish production. While more and more research will be needed. This research gives guideline to the researcher for future study of Ramsagar lake.