Heavy metals (HM) can cause many different problems for aquatics organisms. Cladocerans are of the most important primary consumer of aquatic ecosystems and play a significant role in secondary production and transfer of energy and substances along the food chain. HM absorption by planktonic species can not only lead to the destruction of the planktonic population but also results in bioaccumulation of HM along food chain and finaly harm human as a top consumer. In this study the impact of two different heavy metals such as Pb and Cd concentration on the growth and morphometric characteristics of two Cladocerans species; Daphnia magna and Ceriodaphniaquadrangula was investigated. The examinations were carried out as a complete random plan for 21 days at 24?c. Cladocerans were fed by Scenedesmusquadricauda . In order to investigate D. magna same treatment from two nutritional levels including 2×10 5 and 6×10 5 cell/ml and the four concentrations 0, 15, 48.6 and 150 µgPb /L and four concentrations 0,1.2,3.7 and 6.2 µg Cd /L were checked with 3 replications. In connection to C. quadrangula the impact of two nutritional levels including 2×10 5 and 6×10 5 cell/ml and the four concentrations 0, 15, 37.4 and 100 µgPb/L and four concentrations 0,0.6,1.8 and 4.3 µgCd /L were checked with 3 replications. The results indicated that the toxicity of metals was different according to concentrations of the metal type.Different concentrations of lead and Cadmium had significance impact on the amount of density ,special growth and the doubling time. The highest density ,the maximum growth rate and the shortest population doublings time of D. magna respectrely were 144 individuals/250ml, 0.16 day -1 and 4.3 day and the highest density , the maximum growth rate and the shortest population doublings time of C. quadrangula respectrely were 400 individuals/150ml, 0.16 day -1 and 4.4 day. With increasing the concentrations of lead and cadmium, length and width of the body in both species decreased significantly .The result indicated that the maximum length of body, width of body and length of spine width of D. magna respectrely were 1767.2, 1425 and 841.6 Micron. In C. quadrangula the maximum length and width of body respectrely were 800 and 525.6 Micron. Keywords: Daphnia magna , Ceriodaphniaquadrangula , Heavy metal, Cyclomorphosis, Growth
