The exposure-related effects of a commercially prepared spray-dried powder (SDP) formulation of Pseudomonas fluorescens, strain CL145A, were evaluated on coldwater, coolwater, and warmwater fish endemic to the Great Lakes and Upper Mississippi River Basins. Nine species of young-of-the-year fish were exposed to SDP for 24 hours by using continuous-flow, serial-dilution exposure systems at temperatures of 12 degrees Celsius (°C; 2 species; Oncorhynchus mykiss [rainbow trout] and Salvelinus fontinalis [brook trout]), 17 °C (3 species; Perca flavescens [yellow perch], Sander vitreus [walleye], and Acipenser fulvescens [lake sturgeon]), or 22 °C (4 species; Micropterus salmoides [largemouth bass], Micropterus dolomieu [smallmouth bass], Lepomis macrochirus [bluegill sunfish], and Ictalurus punctatus [channel catfish]).

Treatments, which were nominal target concentrations of SDP (as active ingredient) of 50, 100, 200, and 300 milligrams per liter (mg/L), were continuously applied for 24 hours by the addition of a test article stock solution into the main water inflow of each exposure system's dilution box. The SDP-treated water was then serially diluted through a series of dilution cells before delivery to the test chambers. The exposure concentrations measured were 61.5 to 81.4 percent of the target concentration. After exposure, fish were monitored for 22 days to assess exposure-related latent effects.

Analyses of test animal condition factors and survival revealed that a 24-hour continuous dose of SDP affected all species. Calculated concentrations of SDP that would be lethal to 50 percent of the test animals (LC₅₀) for the coldwater species were 19.2 and 104.6 mg/L for rainbow and brook trout, respectively. The LC₅₀'s for the coolwater species were 185.4, 176.9 and 8.9 mg/L for yellow perch, walleye, and lake sturgeon, respectively. The LC₅₀'s for the warmwater species were 173.6, 139.4, and 63.1 for the largemouth bass, smallmouth bass, and channel catfish, respectively. A reliable LC₅₀ for bluegill sunfish could not be calculated because mortality in the SDP-treated groups did not exceed 20 percent.

Further investigations to evaluate the SDP-exposure related effects on freshwater fish at the maximum approved open-water label concentration and exposure duration (100 mg/L for 8 hours) and using the expected lentic application technique (static application) are warranted. The variation in tolerance to P. fluorescens, strain CL145A, exposure observed in this study indicates that fish species community composition should be considered before SDP is applied in open-water environments.