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One of the hallmarks of invasive species is their propensity to spread. Removing an invasive species after establishment is virtually impossible, and so considerable effort is invested in preventing the range expansion of invaders. Silver carp (Hypophthalmichthys molitrix) were discovered in the Mississippi River in 1981 and have spread throughout the basin. Despite their propensity to expand, the 'leading edge' in the Illinois River has stalled south of Chicago and has remained stable for a decade. Studies have indicated that contaminants in the Chicago Area Waterway System (CAWS) may be contributing to the lack of upstream movement, but this hypothesis has not been tested. This study used a laboratory setting to quantify the role of contaminants in deterring upstream movement of silver carp within the CAWS. For this, water was collected from the CAWS near the upstream edge of the distribution and transported to a fish culture facility. Silver carp and one native species were exposed to CAWS water, and activity, behavior, avoidance, and metabolic rates were quantified. Results showed that silver carp experience an elevated metabolic cost in CAWS water, along with reductions in swimming behavior. Together, results indicate a role for components of CAWS water at deterring range expansion., (© 2024. Amy Schneider, AJ Ensbaugh, Cory Suski. Parts of this work were authored by US Federal Government authors and are not under copyright protection in the US; foreign copyright protection may apply.)

Background: Freshwater ecosystems are some of the most affected by biological invasions due, in part, to the introduction of invasive carp worldwide. Where carp have become established, management programs often seek to limit further range expansion into new areas by reducing their movement through interconnected rivers and waterways. Lock and dams are important locations for non-physical deterrents, such as carbon dioxide (CO 2 ), to reduce unwanted fish passage without disrupting human use. The purpose of this study was to evaluate the behavioral responses of common carp (Cyprinus carpio) to non-physical deterrents within a navigation structure on the Fox River, Wisconsin. Acoustic telemetry combined with hidden Markov models (HMMs) was used to analyze variation in carp responses to treatments. Outcomes may inform CO 2 effectiveness at preventing invasive carp movement through movement pinch-points., Methods: Carbon dioxide (CO 2 ) was recently registered as a pesticide in the United States for use as a deterrent to invasive carp movement. As a part of a multi-component study to test a large-scale CO 2 delivery system within a navigation lock, we characterized the influence of elevated CO 2 and forced water circulation in the lock chamber on carp movements and behavior. Through time-to-event analyses, we described the responses of acoustic-tagged carp to experimental treatments including (1) CO 2 injection in water with forced water circulation, (2) forced water circulation without CO 2 and (3) no forced water circulation or CO 2 . We then used hidden Markov models (HMMs) to define fine-scale carp movement and evaluate the relationships between carp behavioral states and CO 2 concentration, forced water circulation, and temperature., Results: Forced water circulation with and without CO 2 injection were effective at expelling carp from the lock chamber relative to null treatments where no stimulus was applied. A portion of carp exposed to forced water circulation with CO 2 transitioned from an exploratory to an encamped behavioral state with shorter step-lengths and a unimodal distribution in turning angles, resulting in some carp remaining in the lock chamber. Whereas carp exposed to forced water circulation only remained primarily in an exploratory behavioral state, resulting in all carp exiting the lock chamber., Conclusion: Our findings illustrate the potential of forced water circulation, alone, as a non-physical deterrent and the efficacy of CO 2 injection with forced water circulation in expelling carp from a navigation lock. Results demonstrate how acoustic telemetry and HMMs in an experimental context can describe fish behavior and inform management strategies., (© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Objective: The ability to effectively treat parasitic infestations of fish is of high importance for fish culture facilities. However, tools or approved therapies for treating infestations on fish are limited. This paper summarizes results from four separate clinical field studies that evaluated the efficacy of hydrogen peroxide (H 2 O 2 ; 35% PEROX-AID) for reducing Gyrodactylus spp. infestation density., Methods: Three species of Gyrodactylus were studied (G. salmonis, hosts: Brook Trout Salvelinus fontinalis and Lake Trout S. namaycush; G. freemani, host: Yellow Perch Perca flavescens; G. hoffmani, host: Fathead Minnow Pimephales promelas) before and after the application of immersion H 2 O 2 therapy., Result: Parasite density was significantly reduced for each parasite × host combination to which H 2 O 2 therapy was applied. Two clinical field studies in salmonids were found to demonstrate substantial effectiveness that enabled 35% PEROX-AID approval., Conclusion: Further assessments of Gyrodactylus spp. could expand the use of H 2 O 2 for controlling these parasites in aquaculture. Specifically, H 2 O 2 was effective at all levels tested (50 or 75 mg H 2 O 2 /L for 60 min for the Yellow Perch and Fathead Minnow clinical field studies; 100 or 150 mg H 2 O 2 /L for 30 min regardless of salt pre-treatment for the Brook Trout study; and 100 mg H 2 O 2 /L for 30 min or 50 mg H 2 O 2 /L for 60 min for the Lake Trout study)., (Published 2023. This article is a U.S. Government work and is in the public domain in the USA.)

Carbon dioxide (CO 2 ) has been approved by the US Environmental Protection Agency as a new aquatic pesticide to control invasive Asian carps and other aquatic nuisance species in the United States. However, limited CO 2 toxicity data could make it challenging for resource managers to characterize the potential risk to nontarget species during CO 2 applications. The present study quantified the toxicity of CO 2 to 2 native riverine fishes, bluegill (Lepomis macrochirus) and fathead minnow (Pimephales promelas), using 12-h continuous flow-through CO 2 exposure at 5, 15, and 25 °C water temperatures. Resulting survival indicated that bluegill (median lethal concentration [LC50] range 91-140 mg/L CO 2 ) were more sensitive to CO 2 than fathead minnow (LC50 range 235-306 mg/L CO 2 ) across all water temperatures. Bluegill were also more sensitive to CO 2 at 5 °C (LC50 91 mg/L CO 2 , 95% CI 85-96 mg/L CO 2 ) than at 25 °C (LC50 140 mg/L CO 2 , 95% CI 135-146 mg/L CO 2 ). Fathead minnow showed an opposite response and were less sensitive at 5 °C (LC50 306 mg/L CO 2 , 95% CI 286-327 mg/L CO 2 ) relative to 25 °C (LC50 235 mg/L CO 2 , 95% CI 224-246 mg/L CO 2 ). Our results show that CO 2 toxicity can differ by species and water temperature. Data from the present study may inform decisions related to the use of CO 2 as a control tool. Environ Toxicol Chem 2020;39:2247-2255. Published 2020. This article is a U.S. government work and is in the public domain in the USA., (Published 2020. This article is a U.S. government work and is in the public domain in the USA.)