Field Evaluation of Microparticles

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With this study, we will validate the use of microparticles to selectively deliver a control agent to feral bigheaded carps. Prior controlled studies conducted in ponds at the Columbia Environmental Research Center (CERC) in Columbia, Missouri indicated that microparticles could be used to deliver antimycin to bigheaded carps while not impacting non-target species like Largemouth Bass and Grass Carp. 

We conducted the first field trials with an inert microparticle at the Big Muddy National Wildlife Refuge near Arrow Rock, Missouri. This initial field trial indicated that 97.5% of bigheaded carp consume enough microparticle to achieve a lethal dose, while 10 of the 13 other species captured would not have consumed a lethal dose. In this field trial, we expose fishes within an isolated backwater to antimycin-latent microparticle to validate the specificity of the microparticle. This validation will focus on the species impacted by the microparticles as well as the percent of each of these species killed. This trial will be conducted in an isolated backwater to the Wabash River near Lafayette, Indiana using antimycin-latent microparticle. Fish populations in the backwater will be determined prior to the application of microparticles. After the species assessment has been performed, fish will be conditioned to the algal feeding attractant developed at CERC for at least 10 days. Microparticles will be delivered during a single feeding in combination with the algal feeding stimulant once fish have been found to habituate to the algal feeding attractant. As much of the remaining microparticle will be removed as possible from the study site 24 h after application.   Fish mortality will be monitored for the next 96 h. After the 96 h monitoring period, we will seine the study site to capture non-impacted fishes. All fish will be euthanized, identified to species, measured and counted. All fish will then be incinerated.



Bigheaded carps, Silver Carp and Bighead Carp, threaten local economies and aquatic ecosystems across the United States. Established populations exist throughout much of Mississippi River and many of its’ tributaries. Since their accidental release more than 30 years ago, their range in the U.S has expanded and they currently threaten to invade the Laurentian Great Lakes through the Illinois River and the Chicago Area Waterway System. The Illinois River has one of the largest populations of Silver Carp in the world and may comprise up to 95% of the fish biomass in certain areas (MIRCA 2002).

Significant efforts are currently underway to to remove adults bigheaded carps in establish an Integrative Pest Management (IPM) strategy to decrease populations of bigheaded carps at the perceived invasion front. One important component of an IPM is the use of chemicals that can impact adult, juveniles and larva alike. Unfortunately, there are only four USEPA approved piscicides: niclosamide, 3-trifluoromethyl-4-nitrophenol, rotenone, and antimycin-A. Niclosamide and TFM are approved as lampricides, but may not present a viable option as a control tool for bigheaded carps. Antimycin-A and rotenone are non-selective toxicants that are used for reclamation efforts when an entire body of water must be restored and restocked with fish. Unfortunately, both antimycin A and rotenone are not selective. Fishery resource managers have indicated that a lethal control tool selective to bigheaded carps is highly desirable.

Increasing the selectivity of either rotenone or antimycin A is ideal since both are already registered piscicides with the USEPA. Selectivity of rotenone and antimycin A to bigheaded carps could be achieved by exploiting their filter-feeding behavior by delivering the piscicide orally via microparticle. Unfortunately, rotenone is modified into non-toxic chemicals in the digestive system and would be generally useless as an oral toxicant. Whereas, antimycin A maintains toxicity in the gut and is absorbed across the gut membrane making it an ideal candidate control chemical for inclusion into the microparticle. A previous study has demonstrated that antimycin A is more toxic than rotenone when orally delivered of (Rach et al 2009).

Using technologies developed for the pharmaceutical and agricultural industries, it is now possible to manufacture an encapsulated microparticle capable of delivering antimycin A to bigheaded carps. Using spray atomization, we formulated a microparticle that consists of talc, sorbitan, palmitate, and beeswax capable of delivering 4 mg antimycin-A per 100 mg of particle. In controlled laboratory studies, we found 100%, 20%, and 0% mortalities for bigheaded carps, Bluegill, and Largemouth Bass, respectively in tanks where antimycin A-latent microparticles were applied. In duplicated controlled pond trials we killed more than 50% mortality of the bigheaded carp, while no Largemouth Bass or Grass Carp mortality was found.


Even though we are confident that our microparticle is capable of delivering antimycin A to bigheaded carps, two questions still remain: 1) will native planktivorous fishes readily consume the particles and 2) will feral bigheaded carps eat a lethal amount? To begin to answer these two questions, we conducted a field study with an microparticle containing a marker, yttrium, rather than antimycin at an isolated backwater that contained bigheaded carps and native fishes. Results from this study suggest 97.5% of the bigheaded carps would have consumed the microparticle, while only 35.6% of native fishes did. Our next step is to validate these findings with using antimycin A-latent microparticle with a feral population of bigheaded carps. The goal of this project is to determine which species are impacted by the use of antimycin A-latent microparticles.  

USGS scientist making microparticles for use in the field.

USGS scientist making microparticles for use in the field.

(Credit: Justine Nelson, Upper Midwest Environmental Science Center. Public domain.)



1. Identify which species are killed microparticles.

2. Determine how quickly fish die from microparticles.