With increasing consumption and applications of chromium in metallurgy, electroplating, tanning process and stainless steel industry, chromium contamination has become a global environmental problem. In general, Cr(Ⅵ) has higher permeability across the cell membrane than Cr(Ⅲ) and hence is considered more toxic than Cr(Ⅲ). Oxidative stress could be induced following reactive oxygen species (ROS) normally produced in fish under Cr(Ⅵ) exposure due to its variable valences. Furthermore, the intermediates of Cr, e.g. Cr(Ⅴ) and Cr(Ⅳ), produced by cellular reduction processes can bind with DNA and result in mutagenic effects. These combined effects will threaten the growth, development and population structure of different fish species. In this paper, we reviewed published results on the toxic effects of Cr(Ⅵ) in fish at levels of molecules, tissues, organs and individuals. The mechanisms of toxicity and detoxification of Cr(Ⅵ) in various aspects were discussed. In addition, we also put forward perspectives on the toxicity of chromium in aquatic organisms.