Rotenone Toxicity to Rainbow Trout and Several Mountain Stream Insects

Abstract

The piscicide rotenone has been used for over 70 years to eradicate unwanted fish, but controversy exists regarding its impacts on nontarget organisms, particularly aquatic invertebrates. We evaluated the toxicity of synergized Nusyn‐Noxfish and nonsynergized CFT Legumine rotenone formulations in 4‐ and 8‐h exposures to rainbow trout Oncorhynchus mykiss and six species of mountain stream caddisflies, mayflies, and stoneflies. We then compared these results with historical treatment data and aquatic invertebrate collections surrounding rotenone treatments in the 1990s that were designed to restore Paiute cutthroat trout O. clarkii seleniris to the Silver King Creek basin in Alpine County, California. The toxicity of rotenone was greatest to the trout; the synergist piperonyl butoxide appeared to have no effect on the toxicity of rotenone to the trout but did increase the toxicity to the invertebrates. The mean 8‐h concentrations (as rotenone) lethal to 50% of the rainbow trout were 5.3 μg/L for CFT Legumine and 6.2 μg/L for Nusyn‐Noxfish; the mean values for invertebrates ranged from 34 to 174 μg/L for CFT Legumine and from 13 to 74 μg/L for Nusyn‐Noxfish. These findings corresponded to that observed in Silver King Creek, where three annual treatments of 16–23 μg/L for 6–18 h were successful in extirpating rainbow trout hybrids but caused little change in aquatic insect assemblages. To lessen the impacts of rotenone treatment in mountain streams, project planners should (1) use the lowest rotenone concentration and duration needed to accomplish the treatment objective (we suggest 25–50 μg/L for <8 h) and (2) avoid using formulations containing the synergist piperonyl butoxide.

Piscicides and Invertebrates: After 70 Years, Does Anyone Really Know?

“…Thus, scientists and managers must consider effects on invertebrates and the consequences on a case-by-case basis. However, recent work suggests that impacts to invertebrate assemblages can be reduced and mortality to target fish species maintained at lower concentrations than have generally been used in the past (Finlayson et al 2010). To further reduce impacts and enhance recolonization, we recommend the following actions: (1) chemical treatments of larger drainages should stage treatments with intermediate barriers and allow time between treatments for dispersal and recolonization of invertebrates to avoid potential for cumulative impacts; (2) headwater and tributary fishless stream reaches should not be treated so they can serve as refuges for invertebrates; and (3) piscicides should be neutralized downstream of the project area to protect downstream colonization sources.…”

“…Finlayson et al (2010) suggest a mean rotenone concentration of 25-50 ppb for < 8 h should result in complete mortality to salmonids and limited mortality to invertebrates in streams. This rotenone dosage is less than that commonly used in fish removal projects (Table 3).…”

“…For both piscicides, interpretation of the effects on invertebrate assemblages were often contradictory, with some studies reporting few treatment effects on invertebrates (e.g., rotenone -M' Gonigle and Smith 1938;Brown and Ball 1943;Ball and Hayne 1952;Zilliox and Pfeiffer 1960;Cook and Moore 1969;Houf and Campbell 1977;Finlayson et al 2010;antimycinWalker et al 1964;Houf and Campbell 1977;Walker 2003;Moore et al 2005;Hamilton et al 2009) and other studies reporting substantial treatment impacts to invertebrates (e.g., rotenone -Davidson 1930;Cutkomp 1943;Zischkale 1952;Das and McIntosh 1961;Binns 1967;Hamilton et al 2009;antimycin-Jacobi and Deagan 1977;Minckley and Mihalick 1981;Dinger and Marks 2007). The causes of these differences are intriguing and not entirely clear, but to us they appeared due to three factors: (1) piscicide concentration, duration, and treatment breadth; (2) aquatic invertebrate study objectives and sampling intensity; and (3) natural variation in toxicity among species and species groups.…”

Analysis of active rotenone concentration during treatment of the Rondegat River, Cape Floristic Region, South Africa

“…Complete inactivation would have required the neutralisation station to run for longer than 48 h. In the case of the Rondegat River, the presence of active rotenone more than 24 h after the treatment had been terminated is of no concern, as the river runs into Clanwilliam Dam which would have diluted the rotenone to negligible concentrations. Furthermore, the 37.5 μg l −1 rotenone concentration was within the range recommended for eradiating sensitive species and to minimise impacts to non-target aquatic invertebrates (Finlayson et al 2009). Effective neutralisation will, however, be critical for rotenone operations where this is not the case and where there may be impacts on non-target downstream biota such as aquatic invertebrates and amphibians.…”

“…Besides having a strong piscicidal effect, in the aquatic environment rotenone poses a risk to a variety of gill-respiring organisms including tadpoles and macroinvertebrates (Blakely et al 2005;Finlayson et al 2009;Billman et al 2011). Rotenone is a very unstable compound and degrades by a variety of mechanisms including hydrolysis (t ½ -values vary from 2.0 d at pH 9 to 12.6 d at pH 5 [Thomas 1983]), photolysis (t ½  1.4 h [Spare 1982] to 8.2 h [Draper 2002]), and is metabolised by bacteria (Spare 1982), fish (Gingerich andRach 1985) and mammals (Eiseman 1984).…”