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¹ Banaras Hindu University, Zoology Department, Mahila Mahavidyalaya, Varanasi-221005, India DOI : 10.4194/1303-2712-v18_10_07 Viewed : 4470 - Downloaded : 4937 The aim of the present study was to examine comparative effects of different concentrations of heavy metals such as cadmium (Cd), cobalt (Co), lead (Pb) and mercury (Hg) on catfish oocyte maturation and ovulation. Post-vitellogenic oocytes of the catfish H. fossilis were incubated with heavy metals at concentrations of 0.1, 1.0, 10 and 50ng/ml. Translucent follicles without germinal vesicle and opaque follicles with GV were scored after 4, 8, 16, and 24 hr of incubation. Percentage GV breakdown (GVBD) was calculated as an index of oocyte maturation. The results of present investigation suggested that the effect of heavy metals on oocyte maturation and ovulation was in the order of Pb > Hg >Cd>Co. Pb and Hg showed significant increases (P<0.05) in GVBD and ovulation at all concentrations during 4 and 8hr of the incubation. However, there was a dose –dependent decrease at 16 and 24hr. Cd and Co showed decline in GVBD and ovulation at 16 and 24 hr of the incubation. However, mercury and lead showed a stimulatory effect on ovulation at 16 and 24 hr compared to control (P<0.05). Thus, these results suggest that catfish oocytes are differentially influenced by heavy metals and are resistant to them at certain levels. Keywords : Heavy metals, catfish, ovary, oocyte maturation, ovulation