Avoidance response of rainbow trout Oncorhynchus mykiss to hexavalent chromium solutions.

Laboratory tests were conducted on one-year-old rainbow trout Oncorhynchus mykiss to evaluate their ability to detect and avoid hexavalent chromium (Cr(6+)). Test fish were given a choice to discriminate between clean water and Cr(6+) solutions of six sublethal concentrations ranging from 0.0015 to 0.3 mg Cr/L in a counter-current flow, steep gradient chamber. The intensity of avoidance response reached a significant level at test concentrations of 0.003 mg Cr/L and higher, and was directly proportional to the Cr(6+) concentration logarithm. Avoidance threshold was estimated through regression analysis and to be 0.0017 mg Cr/L. This result is approximately sixfold lower than maximum-permitted concentration of 0.01 mg Cr/L accepted as the Lithuanian water-quality guideline for the protection of aquatic life.