Freshwater swamp shrimp (Macrobrachium nipponense) were obtained from the local commercial suppliers. Shrimp were transported to a glass aquarium in our laboratory which was equipped with a water-cycling device; dechlorinated tap water (with a pH of 7.4 ~ 8.1, dissolved oxygen (DO) of 7.0 ~ 7.7 mg/L, and hardness of 38 ~ 45 mg CaCO3 /L) was used during the entire experiment. The temperature was maintained at 24.0 ± 0.5°C, with a 12-h light and 12-h dark photoperiod. Shrimp were acclimated for two weeks and fed an aquarium shrimp mixture every day. Shrimp (0.42 ± 0.17 cm in fork length) were used for acute toxicity tests in the initial experiments. Gallium sulfate (III) and antimony chloride (III) were purchased from Alfa Aesar (Ward Hill, MA, USA). Indium chloride (III), copper sulfate (II), and cadmium chloride (II) were purchased from Sigma (St. Louis, MO, USA). All metal compounds had a purity of 99% or greater. Stock solutions were prepared in deionized water (1000 mg/L test chemical in 0.1% nitric acid).
Laboratory static renewal tests were conducted to determine the median lethal concentration (LC50) for M. nipponense. Ten animals of similar size were randomly sampled and placed in 10-L glass beakers. After 24 h of acclimatization, the M. nipponense were exposed to different concentrations of gallium (0, 0.3, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mg/L), antimony (0, 0.5, 1.0, 2.0, 4.0, 8.0, 12.0, 14.0, and 16.0 mg/L), indium (0, 0.5, 1.0, 2.0, 4.0, 8.0, 12.0, 14.0, and 16.0 mg/L), cadmium (0, 0.002, 0.005, 0.01, 0.05, 0.1, 0.2, 0.4, and 0.6 mg/L), and copper (0, 0.002, 0.005, 0.01, 0.05, 0.1, 0.2, 0.4, and 0.6 mg/L) for 96 h or more. The control and each treated group were run in duplicate. During the experiment, dead animals were removed, with mortality recorded after 24, 48, and 96 h. The LC50 of every test chemical with 95% confidence limits were calculated for M. nipponense using a Basic program from the probit analysis described by Finney[29].