The present study was conducted to evaluate the sensitivity of the Vibrio fischeri bioluminescence inhibition test (Microtox ® assay), and the standard acute Daphnia magna test; using 3 heavy metals, 3 organic pesticides, and their mixtures. In Daphnia tests, either at 24h or 30 min exposure times, the pattern of toxicity order for heavy metals was Cu ˃ Cd ˃ Pb. Chlorpyrifos-methyl was the highest toxic at 24h, while Triazophos was the highest toxic at 30 min exposure times.

The abundance and diversity of zooplankton has been studied in relation to some environmental variables in El-Rayah El-Behery (one of the main irrigating canals of Nile Delta). Eight physical and chemical parameters were investigated for water quality assessment during the period from autumn to winter 2014.The results indicate that, there was negative correlation between temperature, pH and zooplankton. Rotifers have high positive correlation with nutrient and EC, while Protozoa was positively affected by DO. Sixty one species of zooplankton had been identified during the present survey (42 Rotifera, 9 Protozoa, 7 Cladocera and 3 Copepoda).The highest number of species and diversity index (S= 56 and 2.8) were recorded at B1 and B5, while the lowest value was recorded at B6 (S= 40). Rotifers formed a main component of zooplankton, which indicates eutrophic state of El-Rayah El-Behery. Prolides sp. was the main rotifer species during the present study. It was recorded at all sampling stations and was found in all seasons. Vorticella campanula was the most abundant protozoan; it contributed about 42.1% of the total Protozoa populations and flourished in summer. Bosmina longirostris was the most dominant species of cladocera and was represented by about 58.9% of total Cladocera. The highest bulk of total copepods was represented by Nauplius larvae, which recorded about 74.8% of total copepods. There was a sharp increasing in total zooplankton during spring with an average of 1348750 Ind/m³ and a marked decrease during summer with an average number of 635750 Ind/m³.

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