This experiment was carried out to evaluate the effect of an organophosphate pesticide, sumithion on water and sediment quality and benthic invertebrates in aquaculture ponds for 120 days. Three treatments were tried in duplicate: no sumithion (control), weekly application of 1.0mg/L sumithion (Low dose treatment) and 2.0mg/L sumithion (High dose treatment). Among the different water quality parameters, transparency, NO3–N and PO4–P concentrations were significantly (p<0.05) decreased in sumithion high dose and low dose, compared to control. The pH, organic matter (%), available phosphorus (mg/L) and total nitrogen (%) of bottom-sediment also did not vary significantly (p<0.05) among the treatments. Seven genera of benthic invertebrates belonging to Chironomidae, Oligochaeta and Mollusca were identified over the experimental period. The abundances of benthic invertebrates (number perm2) were significantly (p<0.05) decreased in both groups treated with summation, compared to control without pesticide. The findings suggest that sumithion had adverse effect on abundance of benthic invertebrates that might have also negative impact on culture animals in aquaculture ponds

Performance of hybrid red tilapia (Mutant, Oreochromis niloticus×Oreochromis mossambicus) and GIFT tilapia strain (Oreochromis niloticus) in C/N-CP prawn (Macrobrachium rosenbergii) farming system was evaluated at the farmers' pond at Bailor union under Trishal upazilla of Mymensingh district, Bangladesh. The on-farm trial had two treatments: TR and TG (named according to the tilapia strains) with three replications. Six rectangular ponds of varying sizes (400–880m2) were used for this experiment. Hybrid red and GIFT tilapia stains were stocked with prawn at the stocking densities of 1 tilapia fingerlings (either red or GIFT strain) and 3 prawn juveniles m-2 in both treatments. Bamboo side shoot were posted vertically as periphyton substrate. This resulted in an additional substrate surface area of 1067m2 for periphyton development equaling 147% of the pond surface area. Considering the body weight of freshwater prawn only, feeding rates were 10% of body weight at the beginning of the study (up to 30days), and feeding application was gradually reduced to 3% in the last month assuming 80% survival. The abundance of total benthos and periphyton as well as total periphytic biomass were significantly higher (P<0.05) in TR than TG treatment and they were also differed significantly (P<0.05) among different months with a decreasing trends (exception to some extent) over the experimental period. The individual harvesting weight, individual weight gain, specific growth rate, Food Conversion Ratio (FCR), survival (%), gross and net yields of prawn were similar in two treatments. In contrast, the GIFT tilapia strain showed a higher (P<0.05) individual harvesting weight, individual weight gain, specific growth rate ((SGR, % bw d-1), survival, gross and net yields (1935 and 1825kgha-1, respectively) combined gross and net yields (2952 and 2784kgha-1, respectively), and economic return (3755 US$ with BCR 0.82) than the hybrid Red tilapia

Cyanobacteria are major bloom-forming organisms in freshwater ecosystems and many strains are known to produce toxins. Toxin production requires an investment in energy and resources. As light is one of the most important factors for cyanobacterial growth, any changes in light climate might affect cyanobacterial toxin production as well as their growth and physiology. To evaluate the effects of light on the growth and physiological parameters of both toxic and non-toxic strains of Microcystis aeruginosa and Anabaena circinalis, cultures were grown at a range of light intensities (10, 25, 50, 100, 150 and 200 µmol m⁻² s⁻¹). The study revealed that the toxic strains of both species (CS558 for M. aeruginosa and CS537 and CS541 for A. circinalis) showed growth (µ) saturation at a higher light intensity compared to the non-toxic strains (CS338 for M. aeruginosa and CS534 for A. circinalis). Both species showed differences in chlorophyll a, carotenoid, allophycocyanin (APC) and phycoerythrin (PE) content between strains. There were also differences in dark respiration (R_d), light saturated oxygen evolution rates (P_max) and efficiency of light harvesting (α) between strains. All other physiological parameters showed no statistically significant differences between strains. This study suggest that the different strains respond differently to different light habitats. Thus, changes in light availability may affect bloom intensity of toxic and nontoxic strains of cyanobacteria by changing the dominance and succession patterns.