Rainbow (Salmo gairdneri) and steelhead (Salmogairdneri) trout and fathead minnows (Pimephales promelas) were exposed to silver for 96 h in replicated flow‐through tests. Rainbow trout, fathead minnows and Daphnia magna were exposed to silver in replicated static acute tests. Steelhead trout embryo‐larval stages were tested in a flow‐through system for 60 d, and D. magna were exposed through complete life cycles in replicated static‐renewal tests. All silver concentrations were measured values. No differences were seen between flow‐through and static LC50 values. Rainbow trout 96‐h flow‐through LC50 values were 8.6 and 9.7 μg/L silver; static values were 10.9 and 8.5 μg/L. The 96‐h LC50 for steelhead trout in the flow‐through test was 9.2 μg/L. Fathead minnow 96‐h flow‐through LC50 values were 5.6 and 7.4 μg/L silver; static values were 9.4 and 9.7 μg/L. The absence of food in static tests with D. magna caused silver to be about 10 times more toxic; the 48‐h static mean EC50 value for D. magna without food was 0.9 μg/L, compared to 12.5 μg/L in the test with food. The early‐life‐stage test with steelhead trout, from newly fertilized eggs to post‐swimup juveniles, showed complete mortality at 1.3 μg/L and significant reduction in fish survival at 0.5 μg/L silver. Mean weight and length at end of test were greatly reduced at 1.1 μg/L, and were significantly different from controls at 0.1 μg/L. The mean 21‐d EC50 value for the D. magna test with food was 3.5 μg/L. The 21‐d lowest significant (α = 0.05) effect on survival occurred at 4.1 μg/L. The mean silver concentration at which there was a significant decrease in total Daphnia young/female/day after 21 d, compared to the control was 10.5 μg/L silver.

Flow‐through and static tests were conducted with fathead minnows, rainbow trout and Daphnia magna to determine their relative sensitivities to measured concentrations of the insecticide endosulfan and to compare responses of fish in replicated static and flow‐through exposure procedures. Fathead minnow 96‐h static LC50 values were 1.3, 0.8 and 1.3 μg/L endosulfan. The 96‐h LC50 values for fatheads in flow‐through tests were 1.7 and 1.0 μg/L. Rainbow trout 96‐h static LC50 values were 1.7 and 1.6 μg/L. The 96‐h LC50 values for rainbows in flow‐through tests were 0.3 and 0.4 μg/L. Acute 48‐h static EC50 values for D. magna were 343 and 271 μg/L endosulfan. These results suggest that differences in species sensitivity can be as great as three orders of magnitude.

Rainbow (Salmo gairdneri) and steelhead (Salmogairdneri) trout and fathead minnows (Pimephales promelas) were exposed to silver for 96 h in replicated flow‐through tests. Rainbow trout, fathead minnows and Daphnia magna were exposed to silver in replicated static acute tests. Steelhead trout embryo‐larval stages were tested in a flow‐through system for 60 d, and D. magna were exposed through complete life cycles in replicated static‐renewal tests. All silver concentrations were measured values. No differences were seen between flow‐through and static LC50 values. Rainbow trout 96‐h flow‐through LC50 values were 8.6 and 9.7 μg/L silver; static values were 10.9 and 8.5 μg/L. The 96‐h LC50 for steelhead trout in the flow‐through test was 9.2 μg/L. Fathead minnow 96‐h flow‐through LC50 values were 5.6 and 7.4 μg/L silver; static values were 9.4 and 9.7 μg/L. The absence of food in static tests with D. magna caused silver to be about 10 times more toxic; the 48‐h static mean EC50 value for D. magna without food was 0.9 μg/L, compared to 12.5 μg/L in the test with food. The early‐life‐stage test with steelhead trout, from newly fertilized eggs to post‐swimup juveniles, showed complete mortality at 1.3 μg/L and significant reduction in fish survival at 0.5 μg/L silver. Mean weight and length at end of test were greatly reduced at 1.1 μg/L, and were significantly different from controls at 0.1 μg/L. The mean 21‐d EC50 value for the D. magna test with food was 3.5 μg/L. The 21‐d lowest significant (α = 0.05) effect on survival occurred at 4.1 μg/L. The mean silver concentration at which there was a significant decrease in total Daphnia young/female/day after 21 d, compared to the control was 10.5 μg/L silver.

Flow‐through and static tests were conducted with fathead minnows, rainbow trout and Daphnia magna to determine their relative sensitivities to measured concentrations of the insecticide endosulfan and to compare responses of fish in replicated static and flow‐through exposure procedures. Fathead minnow 96‐h static LC50 values were 1.3, 0.8 and 1.3 μg/L endosulfan. The 96‐h LC50 values for fatheads in flow‐through tests were 1.7 and 1.0 μg/L. Rainbow trout 96‐h static LC50 values were 1.7 and 1.6 μg/L. The 96‐h LC50 values for rainbows in flow‐through tests were 0.3 and 0.4 μg/L. Acute 48‐h static EC50 values for D. magna were 343 and 271 μg/L endosulfan. These results suggest that differences in species sensitivity can be as great as three orders of magnitude.