Comparative Freshwater Fish Toxicity Testing of Antimycin A

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Researchers are investigating the influence of Antimycin A on Asian carp and non-target fishes by measuring the effects of a novel species-specific bait formulation.

Antimycin A structure

Figure 1. Chemical structure of Antimycin A. Antimycin A is a nine-membered bis-lactone having methyl substituents at the 2- and 6-positions, an n-hexyl substituent at the 8-position, an acyloxy substituent at the 7-position and an aroylamido substituent at the 3-position. 

(PubMed PMID: 30371825)

The Science Issue and Relevance: The use of a piscicide in ecosystems is a reasonable method to remove invasive species bighead carp (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix) from a water body, similar to the use of a lampricide against sea lamprey. The commercially unavailable Fintrol®, formerly used to remove scaled fish from catfish ponds, has an active ingredient Antimycin A (Fig. 1) that is produced by Streptomyces bacteria. Investigating the influence of this active ingredient on Asian carp and non-target fishes directly relates to measuring the effects of a novel species-specific toxic bait formulation containing Antimycin A. Our hypothesis is that cellular toxicity to Asian carp will be expressed in a concentration- and species-dependent manner, reflecting a similar whole-body response.

Antimycin A binding site

Figure 2. Location of molecular binding site of Antimycin A within a mitochondrion (arrow)

(Image Courtesy of Molecular Expressions)

Methodology for Addressing the Issue: Because Antimycin A is insoluble in water, experiments must first be performed to determine whether the solvent (also known as the vehicle) necessary for dissolving the chemical can itself cause cellular toxicity. This testing of potential vehicles is necessary prior to making various dilutions of the Antimycin A in the vehicle selected that will be used for fish blood cell exposure, then ultimately in bait formulations. Antimycin A targets the cytochrome B subunit Qi of complex III of the electron transport chain, with our biological endpoint being mitochondrial membrane potential, or mitochondrial function (Fig. 2). Comparative amino acid sequence differences within the relevant protein subunits of target species, like Asian carp (bighead-, silver- and grass carp [Ctenopharyngodon idella]), and non-targets, including bluegill sunfish (Lepomis marcrochirus), fathead minnow (Pimephales promelas), channel catfish (Ictalurus punctatus), and common carp (Cyprinus carpio), show that there are a number of variants that could respond differentially to treatment. The Antimycin A in the selected vehicle will be delivered to the various fish species’ blood cells. Mitochondrial membrane potential will be measured with flow cytometry (Fig. 3) and differences in damage level among the fish species will be assessed.

 

Antimycin A solvent vehicles

(Public domain.)

Future Steps: USGS WARC scientists will continue to collaborate with USGS CERC in testing this active ingredient and other potential chemicals against cellular targets in Asian carp, including black carp (Mylopharyngodon piceus) to advance management options for controlling invasive Asian carp species in aquatic ecosystems of concern. The information will be used by partner state- and DOI agencies to help guide their management options.