Flow-through toxicity tests were conducted on common freshwater fishes: rainbow trout (Oncorhynchus mykiss), three-spined stickleback (Gasterosteus aculeatus), roach (Rutilus rutilus), perch (Perca fluviatilis) and dace (Leuciscus leuciscus), to estimate their sensitivity to acute toxicity of nickel. The 96-hour median lethal concentration (96-hour LC50) values obtained from the tests ranged from 19.3 to 61.2 mg Ni/l. According to nickel sensitivity, the species tested may be arranged in the following sensitivity order: rainbow trout > three-spined stickleback > perch = roach > dace. Obtained data could be successfully applied in solving theoretical and practical goals of aquatic toxicology.