Movement and behavioral states of common carp (Cyprinus carpio) in response to a behavioral deterrent in a navigational lock.

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 (CO2), 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 CO2 effectiveness at preventing invasive carp movement through movement pinch-points. METHODS: Carbon dioxide (CO2) 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 CO2 delivery system within a navigation lock, we characterized the influence of elevated CO2 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) CO2 injection in water with forced water circulation, (2) forced water circulation without CO2 and (3) no forced water circulation or CO2. We then used hidden Markov models (HMMs) to define fine-scale carp movement and evaluate the relationships between carp behavioral states and CO2 concentration, forced water circulation, and temperature. RESULTS: Forced water circulation with and without CO2 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 CO2 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 CO2 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.

Efficacy of hydrogen peroxide to reduce Gyrodactylus species infestation density on four fish species.

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 (H2 O2 ; 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 H2 O2 therapy. RESULT: Parasite density was significantly reduced for each parasite × host combination to which H2 O2 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 H2 O2 for controlling these parasites in aquaculture. Specifically, H2 O2 was effective at all levels tested (50 or 75 mg H2 O2 /L for 60 min for the Yellow Perch and Fathead Minnow clinical field studies; 100 or 150 mg H2 O2 /L for 30 min regardless of salt pre-treatment for the Brook Trout study; and 100 mg H2 O2 /L for 30 min or 50 mg H2 O2 /L for 60 min for the Lake Trout study).

Toxicity of Carbon Dioxide to Freshwater Fishes: Implications for Aquatic Invasive Species Management.

Carbon dioxide (CO2 ) 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 CO2 toxicity data could make it challenging for resource managers to characterize the potential risk to nontarget species during CO2 applications. The present study quantified the toxicity of CO2 to 2 native riverine fishes, bluegill (Lepomis macrochirus) and fathead minnow (Pimephales promelas), using 12-h continuous flow-through CO2 exposure at 5, 15, and 25 °C water temperatures. Resulting survival indicated that bluegill (median lethal concentration [LC50] range 91-140 mg/L CO2 ) were more sensitive to CO2 than fathead minnow (LC50 range 235-306 mg/L CO2 ) across all water temperatures. Bluegill were also more sensitive to CO2 at 5 °C (LC50 91 mg/L CO2 , 95% CI 85-96 mg/L CO2 ) than at 25 °C (LC50 140 mg/L CO2 , 95% CI 135-146 mg/L CO2 ). Fathead minnow showed an opposite response and were less sensitive at 5 °C (LC50 306 mg/L CO2 , 95% CI 286-327 mg/L CO2 ) relative to 25 °C (LC50 235 mg/L CO2 , 95% CI 224-246 mg/L CO2 ). Our results show that CO2 toxicity can differ by species and water temperature. Data from the present study may inform decisions related to the use of CO2 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.