Environmental Engineering Reference
In-Depth Information
water (McClay 2000). Some liquid rotenone formulations have generated public
opposition due to the toxicity or smell of hydrocarbon components of the formu-
lations. However, a recent European product (CFT legumine) is reportedly less
noxious (CDFG 2007). Fish species sensitivity to rotenone varies considerably but
fi sh are generally more sensitive than aquatic invertebrates, although signifi cant
invertebrate mortality or drift usually accompanies rotenone applications, given
the relatively high concentration applied to ensure satisfactory mixing and rapid
fi sh kills. Importantly, birds and mammals are relatively insensitive to rotenone
and its use in the USA for nearly a century to eradicate nuisance fi sh from water
bodies, including public water supply reservoirs, without signifi cant ecological
or public health concerns testifi es to its relative safety in this regard (Ling 2003).
A recent development is rotenone-impregnated baits for the control of grass carp
and common carp (Fajt 1996). These baits have demonstrated some promise in
fi sh control under experimental conditions but have sometimes been problematic
in fi eld applications causing signifi cant collateral mortality of non-target species
(Gehrke 2003).
Antimycin-A (Fintrol
®
)
The popularity of antimycin for fi sh control peaked in the 1970s, approaching
that of rotenone, but it has since declined signifi cantly due to cost and availability
(Finlayson
et al
. 2002). US fi sheries agencies used 94.7 t of rotenone in the 10-year
period from 1988-1997, compared with only 50 kg of antimycin in the period
1991-2000. It is registered for use for fi sh control only in the USA and marketed
as Fintrol®. It is highly toxic to scaled fi sh, less toxic to scaleless fi sh such as catfi sh,
and relatively non-toxic to other aquatic life. The differential sensitivity of scaled
and non-scaled fi shes means that most of the antimycin use in the USA is by cat-
fi sh farmers to selectively remove nuisance scaled fi sh species from their ponds
(Finlayson
et al
. 2002). Antimycin baits have been experimentally tested on com-
mon carp and doses of around 1 mg/kg of fi sh are lethal but they have not been
widely applied for fi sh control.
Natural saponins
Saponins are a diverse group of compounds mainly derived from plants. Two
products—teaseed cake and mahua oil cake—have been widely used in Asian
countries, primarily for the renovation of aquaculture ponds, either to remove
fi sh prior to stocking or to eradicate fi nfi sh from shrimp ponds. Toxicity is much
greater to fi nfi sh than to other aquatic organisms such as shrimps, and is enhanced
at higher temperatures and salinities. Both teased cake and mahua oil cake are rela-
tively impure horticultural by-products whose saponin content is variable. Pure
saponin is toxic to fi sh at concentrations of around 0.5-1.0 mg/L but effective
applications of the cake products are typically 25-100-fold greater. Saponins are
not currently registered with any national pesticide regulatory authorities for inva-
sive fi sh control.
