Since gallium is a metal ion used in semiconductor industry, the toxicological effects were previously evaluated in mammals but the ecotoxicological impacts remain unknown. In term of ecotoxicological risk assessment, the median lethal concentration (LC50 for 96 h of gallium to carp (Cyprinus carpio L.) and the oxidative response of carp phagocytes after the fish were exposed to sublethal levels of gallium were determined. The LC50 of gallium on C. carpio at 96 h was estimated as 96.25 +/- 14.3 mg/L. To determine the effect in vivo of gallium on the phagocyte response, fish were exposed for 96 h to 5 or 50 mg Ga(3+)/L. Carp maintained for 48 or 96 h in water containing 50 mg/L gallium had a significant fall in phagocyte oxidative burst activity in comparison with controls, as well as decreased leukocyte number in blood and increased cytotoxicity. To determine the effect in vitro of gallium on the phagocyte response, isolated phagocytes were exposed for 5 or 15 min to 50 nM, 500 nM, or 5, 50, 100, or 200 microM of Ga(3+). The oxidative burst was increased after in vitro incubation of phagocytes with 50 or 500 nM gallium for 15 min or with 500 nM gallium for 5 min. Moreover, for 50, 100, or 200 microM gallium, the oxidative burst activity of carp phagocytes was significantly decreased. Results indicate that the lethal toxicity of gallium for carp of gallium is not as high as for other metal ions. However, gallium was immunosuppressive for carp at the highest concentrations used (from 50 microM) in vivo and in vitro. At low concentrations, it could be an immunostimulant as observed in vitro.