The present study provides a characterization of water quality and plankton samples in earthen fish pond in Rajshahi, Bangladesh. Sampling was done over a period of six months, running from October, 2004 through March, 2005. All the water quality parameters were within the optimal ranges for plankton productivity. Temperatures varied from 19.75 to 27.25 degrees C; transparency, 24.75-29.50 cm; pH, 6.62-7.85; Dissolved Oxygen (DO), 3.87-5.85 mg L(-1); free CO2 5.25-7.25 mg L(-1) and bicarbonate (HCO3) alkalinity, 81.25-147.5 mg L(-1). Analyses of plankton samples recorded a total of 5 classes phytoplankton viz.; Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae and 2 classes of zooplankton; Crustacea and Rotifera. The phytoplankton population was comprised of 17 genera belonging to Cyanophyceae (5 classes, 34.47%), Bacillariophyceae (3, 13.87%), Cyanophyceae (3, 34.48%), Euglenophyceae (3, 10.68%) and 1 to Dinophyceae (6.50%). The zooplankton population consisted of 10 genera belonging to Rotifera (4, 40.13%) and Crustacea (6, 59.87%). Phytoplankton and zooplankton abundance varied from 60800 to 239400 units/l and 7620 to 12160 units/l, respectively. It is concluded that the phytoplankton groups provide the main support for earthen pond aquaculture in the pond compared to zooplankton classes. The information provides for more research to compare water quality and pond plankton characteristics in earthen aquaculture systems with and without fish stocking. Further studies on the seasonal changes of water quality parameters and its effects on plankton production in the fish ponds and all year extended monitoring is recommended in future studies.

Length frequency based population dynamics of the small indigenous cyprinid fish, Amblypharyngodon mola from the Kaptai lake (an artificial water reservoir), Bangladesh were studied using the computer based FiSAT program. Growth parameters La and K were found to be 104.65 mm and 0.95 year-1 respectively. The annual rate of natural mortality (M), fishing mortality (F) and total mortality (Z) were found to be 1.22, 2.04 and 3.26 respectively. Exploitation rate (E) was 0.63, while maximum yield per-recruit (Emax) was estimated as 0.678. The suitable selection pattern (L50) was found to be 51.09 mm. The yield per recruit and biomass per recruit determined as a function of Lc/La and M/K were estimated as 0.49 and 1.28 respectively. The Wetherall plot provided estimates of La and Z/K were 103.38 mm and 3.31 respectively. Growth performance index (?? = 4.017) was found to be suitable. Virtual population analysis (VPA) showed that the maximum number of A. mola was caught between the total length of 75 to 93 mm with values of F exceeding to 2.04 year-1. The estimated mean biomass was found to be 2.81 metric tons. The fish was recruited in the fishery during March to October with maximum in July. DOI: http://dx.doi.org/10.3329/cujbs.v4i1.13398 The Chittagong Univ. J. B. Sci.,Vol. 4(1&2):141-151, 2009