The objective of the present study was to analyze the effect of chronic cadmium (Cd) exposure at two alkalinity levels (63 and 92 mg l(-1) CaCO(3)) on the antipredatory behavior of juvenile silver catfish (Rhamdia quelen) exposed to conspecific skin extract and predator odor. At an alkalinity of 63 mg l(-1) CaCO(3), 30 days of exposure to either 4.5 or 8.0 microg l(-1) Cd impaired the catfish's antipredatory response to alarm cues. However, silver catfish exposed to 4.5 microg l(-1) Cd at an alkalinity of 92 mg l(-1) CaCO(3) responded to skin extract and predator odor. In catfish exposed to 8.0 microg l(-1) Cd at the same alkalinity, only the number of feeding bites decreased, and this occurred only for specimens exposed to predator odor. Our results show that higher alkalinity protected against the deleterious effects of Cd on alarm cue detection but only in the larvae exposed to the lowest waterborne Cd level.