Malachite green (MG) is still being used as an antiparasitic and antifungal agent in aquaculture. This is due to the fact that many farmer owners are not aware of the potential genotoxic and carcinogenic properties of MG. One hundred fish samples were collected from different fish farms at El- Fayoum governorate (Egypt), and the incidence of Malachite green (MG) residue was determined by using an enzyme-linked Immunosorbant assay (ELISA). The data obtained in the present work proved that 59 samples of fish out of 100 (59%) showed the presence of malachite green residues in Oreochromis niloticus and Mugil ephalus samples with an incidence of 28 (56%) and 31 (62%). The mean values of malachite green levels in the examined Oreochromis niloticus and Mugil cephalus samples were 1.603 ±0.165 ppb and 1.244 ±0.114 ppb. Heat treatment has high effect on malachite green residues, as mean values before and after frying were 2.49±0.234 and 0.94±0.277, for roasting 2.49±0.234 and 1.62±0.245 and for microwaving 2.49±0.234 and 0.62±0.233 respectively, with reduction percent for frying, roasting and microwaving were 62.25 %, 34.94 % and 75.1 % respectively. The results revealed that, freezing had trivial effect on malachite green residues, as reduction percent after freezing for three months was 0.8 %. Statistical analysis by using One-Way ANOVA test revealed that there are highly significant differences (p<0.01) between different mean values and different reduction percent recovered from frying, roasting and microwaving. Comparing the results of malachite green residues in examined Oreochromis niloticus and Mugil cephalus samples with Commission Regulation (EU, 2004) for maximum residues limits, it was clear that 16 (16%) of examined samples were more than
MRLs which is 2 µg/kg