Experimental studies of rainbow trout populations exposed to field applications of Roundup herbicide.

This paper reports the effects of Roundup herbicide (MON 02139) on rainbow trout viability and behavior in several field experiments at the University of British Columbia Research Forest. Laboratory and field 96-hr LC50 values were similar: 54.8 and 52.0 mg/L. Avoidance-preference data indicated that fish would avoid lethal levels of Roundup. Operational application of Roundup at the recommended field dose of (2.2 kg a.e./ha), as well as 10x and 100x field dose resulted in no mortality to rainbow trout in field streams. Results indicate that operational spraying with this herbicide for weed control should not be detrimental to rainbow trout populations. Improper use or accidental spills of Roundup could be avoided by rainbow trout and should not be lethal if diluted in a moderately-flowing stream.