Research Article
Md. Jahangir Sarker, Farhana B
Abstract
The present study was conducted to quantify the water quality parameters and plankton concentrations of the Meghna river estuary during the spawning season of Hilsa (Tenualosa ilisa) and also to establish knowledge about the habitat. Hilsa (Tenualosa ilisha) is one of the flagship anadromous fish species of Bangladesh that migrate downstream for spawning purposes only through the Ganges-Meghna river system route. The study period constitutes two spawning seasons of Hilsa (Tenualosa ilisha) (June 2014 and February, March 2015). The water quality parameters and plankton concentrations were measured and analyzed by standard methods. A total of 50 genera of plankton identified from the water body belonging to the group Bacillariophyceae, Cyanophyceae, Chlorophyceae, Dinophyceae, Coscinodiscophyceae, Copepoda, Rotifera, Cladoceran, Protozoa, Crustacean larvae and Meroplankton. The phytoplankton density was varied from 2.93×103 to 7.94×103 cells/L and zooplankton density of 1.15×103 cells/L to 1.8×103 cells/L. The plankton concentrations were strongly correlated with the fluctuations of water quality. The water temperature and phytoplankton density was positively correlated (r = 0.75), on the other hand, negative correlation was found between phyplankton and transparency (r = - 0.84). Bacillariophyceae was the most dominant group contributing 78% of phytoplankton and among zooplankton, Copepoda contributes 36%. Shannon-Weiner species diversity index (Hʹ) used as an indicator of water quality. It ranged from 2.07 to 2.74 (phytoplankton) and 1.82 to 2.38 (zooplankton). The mean value of phytoplankton was 2.42 ± 0.19 and zooplankton was 2.14 ± 0.16 and it was within the range of 1 to 3, so the water body is moderately polluted. The phytoplankton cell density is a good indicator to determine the trophic status of a particular water body. The mean cell density of phytoplankton was 5372 cells/L and could be classified as oligotrophic. Oligotrophic water body characters lack nutrients which resulted in the lowest density of plankton. Based on plankton density it can be concluded that during spawning season, plankton profile is low which might be hindered Hilsa to migrate this spawning ground.