Hilsa (Tenualosa ilisha) is one of the flagship diadromous fish species of Bangladesh that migrate only through the Ganges-Meghna river system route. The biological profile of plankton from the Padma, Meghna and Tetulia reference river sites during 2011 spawning season of hilsa showed that in total of 58 taxa of plankton were present. Of which, 19 taxa (32.76%) were of phytoplankton and 39 taxa (67.24%) of zooplankton. Phytoplankton group belonged to Cyanophyceae (6 taxa), Chlorophyceae (7 taxa) and Bacillariophyceae (6 taxa) while zooplankton including Protozoa (10 taxa), Rotifera (19 taxa), Copepoda (4 taxa), Cladocera (5 taxa) and Ostracoda (1 taxon). The average abundance of plankton was recorded as 194.05 ± 82.58 indiv/l. The highest abundance of total plankton (692 indiv/l) was observed in Godagari, Rajshahi (Station 3) and was lowest (4.00 indiv/l) in Charghat, Rajshahi (Station 2). The highest abundance (49 indiv/l) of total zooplankton was observed in Godagari and lowest (1 indiv/l) in Charghat with mean value of 19.46 ± 4.12 indiv/l. The highest species richness (SR = 45) was observed in Daulotkhan, Vhola (Station 9) and the lowest (SR = 3) in Charghat (Station 2), with mean value of 17.10±4.408. Shannon-Weiner species diversity index (Hʹ) ranged from 3.334 in Daulotkhan (Station 9) to 1.5 in Charghat, (Station 2) with mean value of 2.717 ± 0.147. Based on the plankton profile it may be concluded that the biological quality of hilsa migratory river was not alike throughout the route which may restrict the migration up to up steam and spontaneous spawning of hilsa.

Some physico-chemical parameters of Chandbill Baor, a natural oxbow lake of Meherpur district were studied from September 2006 to August 2007. Air temperature of the study area varied from 18.10 to 32.10°C ( x ± SE : 27.73 ± 1.22°C). The Water temperature (17.10 to 32.10°C; x ± SE: 28.24 ± 1.32°C), Secchi disc depth (8.89 to 53.34 cm; x ± SE : 26.19 ± 4.29 cm), water depth (132.08 to 307.34 cm; x ± SE : 183.93 ± 13.88 cm); total alkalinity (51.3 to 85.5 mg/l; x ± SE : 68.4 ± 3.64 mg/l), total hardness (85.5 to 188.10 mg/l; x ± SE : 125.81 ± 9.38 mg/l), dissolved oxygen (5.0 to 12.0 mg/l; x ± SE: 8.42 ± 0.62 mg/l), free CO2 (5.0 to 30.0 mg/l; x ± SE : 14.58 ± 2.64 mg/l), pH (8.0 to 10; x ± SE : 8.54 ± 0.19), ammonianitrogen (0.3 to 0.7 mg/l; x ± SE: 0.46 ± 0.04 mg/l) in the 'Baor' water were found to be suitable for survival of aquatic fauna. Nitrite-nitrogen was absent in the 'Baor' throughout the year. Positive correlations were observed in between air and water temperature (r = 0.978); free CO2 and Secchi depth (r = 0.839), free CO2 and water depth (r = 0.714); water depth and Secchi depth (r = 0.903); total hardness and total alkalinity (r = 0.861) and pH with DO (r = 0.661). However, inverse relations were observed among ammonia-nitrogen with water depth (r = −0.727); ammonia-nitrogen with Secchi disc depth (r = −0.840); dissolved oxygen with free CO2 (r = −0.636); pH with Secchi disc depth (r = −0.581) and pH with free CO2 (r = −0.825). The productivity of the lake was found to be medium and could be improved to higher level. Alkaline pH (8.54 ± 0.19) was supposed to be helpful for proper growth and development of fishes and aquatic organisms. This is the first limnological report from a natural 'Baor' (Oxbow lake) of Meherpur district, Bangladesh.

This study deals with the zooperiphyton communities of Dhanmondi lake, Dhaka, Bangladesh using bamboo, mehegoni and rain tree sticks as substrates along with some physicochemical features of the lake water. It was revealed that zooperiphyton communities constitute protozoa, rotifera, copepoda, cladocera, ostracoda, conchostraca, insect larvae, oligochaeta, nematoda and mollusca. Rotifera (41%), protozoa (31%) and ostracoda (14%) were the dominant groups of zooperiphyton. Among protozoans, Epistylis sp. (52%) and Arcella sp. (20%); among rotifera, Rotaria neptunia (32.88%), Anuraeopsis fissa (17%) and Brachionus angularis (12%); among copepoda, naupleus (52%) and Cyclops sp. (32%); among cladoceran, Chydorus sp. (28%); among ostracods, Cypris sp. (100%); among molluscs, Bellamya sp. (75%) and Brotia sp. (22%) were found to be the most dominant species. The average number of zooperiphyton was 43023.55 ± 5891.34 individual m-2 recorded from all substrates. During the study period, the physicochemical features of water of Dhanmondi lake were found to be suitable for aquatic biota. It can help in enhancing the productivity as well as sustain the aesthetic value of the lake.Bangladesh J. Zool. 41(1): 61-71, 2013