The LC50 of two anaesthetic agents, clove essence and MS222, on the cultivated fish species, Acipenser persicus, Oncorhynchus mykiss, Cyprinus curpio were estimated. 640 samples of above mentioned species were used exposing anaesthetic agents for 2 minutes.LC50 of clove essence and MS222 for sturgeon estimated 297 and 291 ppm, for common carp was 271 and 272 ppm; and for rainbow trout Was 199 and 207 pmm, respectively. Significant difference was found only between LC50 of MS222 in rainbow trout with LC50 of both agents in two other species. Also, the results showed that there is no significant difference on poisoning of two applied drugs in all above mentioned species; with comparing different species, rainbow trout had lower tolerance to both anesthetics
