Efficacy of Chloramine‐T to Control Mortality in Freshwater‐Reared Salmonids Diagnosed with Bacterial Gill Disease

Bowker, James D.; Carty, Daniel; Telles, Larry; David, Bob; Oviedo, D.

doi:10.1577/a06-042.1

Cited by 13 publications

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“…Hypochlorite ions that form *Corresponding author: jim bowker@fws.gov Received March 16, 2015;accepted May 10, 2015 when CLT is dissolved in water (Booth and McDonald 1988) are strong oxidizers that can quickly destroy cellular material and disrupt essential cell processes (Powell and Clark 2003). Chloramine-T has been shown to effectively control the mortality associated with bacterial gill disease (BGD) in salmonids 525 (from 1980;Speare and Ferguson 1989;Bullock et al 1991; Thorburn and Moccia 1993;Ostland et al 1995;Bowker and Erdahl 1998;Bowker et al 2008b) and with external columnaris in Largemouth Bass Micropterus salmoides and Bluegill Lepomis macrochirus (Bowker et al 2013). The toxicity of CLT to fishes has also been investigated (Bills et al 1988;Powell et al 1995Perry 1996, 1998;Sanchez et al 1996Sanchez et al , 1997King and Farrell 2002;Powell and Harris 2004;Gaikowski et al 2008Gaikowski et al , 2009Bowker et al 2011), with results indicating an adequate margin of safety when it is used according to established treatment protocols.…”

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“…As part of the effort to obtain FDA approval of the use of CLT in U.S. aquaculture, researchers at the U.S. Fish and Wildlife Service (FWS) Aquatic Animal Drug Approval Partnership program conducted CLT efficacy (EFF) studies on Rainbow Trout Oncorhynchus mykiss, Apache Trout O. apache, and Chum Salmon O. keta (Bowker et al 2008b), and target animal safety (TAS) studies on Rainbow Trout (Bowker et al 2011). Though all CLT doses administered in these studies were analytically verified and found to be within FDA-acceptable limits (i.e., target dose ± 25%), all had been administered in standing-bath treatment conditions.…”

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Considerations for Consistently Applying Flow‐Through Chloramine‐T Treatments to Hatchery Raceways

et al. 2015

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Chloramine‐T (CLT) was recently approved for use in the United States by the U.S. Food and Drug Administration (FDA) to control mortality in selected freshwater‐reared finfishes diagnosed with bacterial gill disease or external columnaris disease. In support of this approval, we conducted a study to determine if a target dose of 12 mg/L CLT could be delivered for 60 min via a “charged,” flow‐through treatment protocol. The study was conducted in two production‐size, linear‐design, plug flow raceways devoid of fish. Each raceway was dosed twice, resulting in four replicate trials (N = 4). During each trial, CLT was added under static conditions to establish a target concentration of 12 mg/L. Inflow water was then resumed, and additional CLT stock solution was metered into the raceway for the 60‐min treatment period. Water samples were collected from a matrix of 27 sampling locations (3 positions along raceway length × 3 positions across raceway width × 3 depths) for colorimetric determination of CLT concentrations at 0 min (after charging but before resuming water inflow), 30 min, and 60 min. Chloramine‐T doses delivered (data from all sampling locations and times pooled) did not vary from trial to trial. Median CLT doses delivered were almost always less than 12 mg/L; however, all had corresponding 95% confidence intervals within 9–15 mg/L. Overall, the results of our study demonstrated that the treatment method can be used to deliver a target dose of CLT for 60 min in production‐size raceways in a manner that was found acceptable to the FDA.

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Considerations for Consistently Applying Flow‐Through Chloramine‐T Treatments to Hatchery Raceways

et al. 2015

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“…Chloramine-T (C 7 H 7 ClNNaO 2 S·3H 2 O) is a biocide used worldwide as a disinfectant and antiseptic. Although CLT has been used for years under authorization of publically held Investigational New Animal Drug (INAD) exemptions and has been shown to effectively control mortality associated with BGD in freshwater-reared salmonids (From 1980;Speare and Ferguson 1989;Bullock et al 1991;Thorburn and Moccia 1993;Ostland et al 1995;Bowker and Erdahl 1998;Bowker et al 2008) and columnaris in a variety of freshwater finfish, it is not yet approved by the U.S. Food and Drug Administration (FDA) for use on fish.…”

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Controlling Mortality Caused by External Columnaris in Largemouth Bass and Bluegill with Chloramine‐T or Hydrogen Peroxide

et al. 2013

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Columnaris (causative agent, Flavobacterium columnare) is a widespread fish disease of concern among fish culturists in the USA. If left untreated, an entire population of fish may become infected, and morbidity and mortality may reach high levels. In virtually all instances, columnaris outbreaks require intervention to prevent significant losses. A number of sanitizing agents, most notably chloramine‐T (CLT) and hydrogen peroxide (HP), have been used to control mortality associated with a variety of bacterial pathogens causing external infections. However, the majority of trials conducted to demonstrate the effectiveness of these chemicals, thereby gaining U.S. Food and Drug Administration approval for their use in treating fish infected with columnaris, have been conducted on salmonids. Accordingly, we conducted seven experiments to evaluate the effectiveness of CLT or HP to control mortality associated with external columnaris in Florida Largemouth Bass Micropterus salmoides floridanus and Bluegill Lepomis macrochirus. Treatment with CLT or HP significantly reduced cumulative mortality in five of the seven experiments. Cumulative mortality was strongly correlated to pretreatment mortality in treated and control tanks in the five Largemouth Bass experiments, suggesting that intervention at later stages of columnaris progression may result in less favorable outcomes. Odds ratios calculated for individual experiments indicated varying degrees of success in controlling mortality; however, meta‐analysis of all experiments indicated treatment with either CLT or HP significantly increased probability of survival, regardless of fish species or test article. These results demonstrate that both chemicals can be effective in controlling mortality associated with external columnaris in Largemouth Bass and Bluegills and that timely treatment of fish will likely result in lower overall mortality.

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“…Consequently, efforts have been underway for many years to obtain a NADA for CLT for use in U.S. aquaculture to control mortality in freshwater-reared finfish caused by bacterial gill disease (BGD; causative agent, Flavobacterium branchiophilum) and other external flavobacterial infections. Chloramine-T effectively controls BGD-related mortality in salmonids (From 1980;Speare and Ferguson 1989a;Bullock et al 1991; Thorburn and Moccia 1993;Ostland et al 1995;Bowker and Erdahl 1998;Bowker et al 2008). The toxicity of CLT to fishes has also been investigated (Bills et al 1988;Powell et al 1994Powell et al , 1995Perry 1996, 1998;Sanchez et al 1996Sanchez et al , 1997King and Farrell 2002;Powell and Harris 2004); however, these studies were not designed to meet current FDA TAS testing requirements (USFDA Center for Veterinary Medicine 1989Medicine , 1999.…”

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“…For salmonids, the proposed CLT treatment regimen is to administer the drug at 12-20 mg/L in a static or flow-through bath for 60 min/d on three alternate or consecutive days (Bowker et al 2008). To evaluate the safety of this proposed treatment regimen, we conducted eight TAS experiments with CLT on a representative salmonid, rainbow trout Oncorhynchus mykiss.…”

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Chloramine‐T Margin‐of‐Safety Estimates for Fry, Fingerling, and Juvenile Rainbow Trout

et al. 2011

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Chloramine-T (CLT) is a candidate for approval for use in U.S. aquaculture to control mortality in freshwaterreared salmonids caused by bacterial gill disease (causative agent, Flavobacterium branchiophilum). The proposed treatment regimen is to administer CLT at 12-20 mg/L in a static or flow-through bath for 60 min/d on three alternate or consecutive days. To estimate a CLT margin of safety, defined as the highest dosing regimen above the proposed maximum therapeutic regimen at which no adverse effects are observed, we conducted seven experiments with fry, fingerling, and juvenile rainbow trout Oncorhynchus mykiss that examined mortality and an eighth experiment that examined mortality, gross pathology, and histopathology after CLT exposure. In each experiment, triplicate groups of fish were exposed to a range of CLT concentrations representing 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 5× the highest proposed dose (20 mg/L) for 3× the proposed treatment duration (60 min) on three alternate or consecutive days at 8 • C or 14 • C. The survival of fry and fingerlings was unaffected by exposure to CLT concentrations as high as 100 and 60 mg/L, respectively (survival = 97.3-100%). Although the survival of juvenile fish was unaffected by exposure to 20 mg/L, exposure to higher CLT concentrations significantly reduced survival (≤10.0% at 100 mg/L). Across experiments, 92% of all mortalities occurred within 20 h of the first exposure to CLT. The histopathological changes of most concern were associated with gill tissues, but these were evident only in moribund fish exposed to doses of 60 mg/L or higher. Based on analysis of the survival data, the margin-of-safety estimates were approximately 100 mg/L for rainbow trout fry, at least 60 mg/L for fingerlings, and 50-60 mg/L for juveniles. Tissue responses to CLT at these concentrations were minor and did not warrant decreasing these estimates.

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Efficacy of Chloramine‐T to Control Mortality in Freshwater‐Reared Salmonids Diagnosed with Bacterial Gill Disease

Cited by 13 publications

References 10 publications

Considerations for Consistently Applying Flow‐Through Chloramine‐T Treatments to Hatchery Raceways

Considerations for Consistently Applying Flow‐Through Chloramine‐T Treatments to Hatchery Raceways

Controlling Mortality Caused by External Columnaris in Largemouth Bass and Bluegill with Chloramine‐T or Hydrogen Peroxide

Chloramine‐T Margin‐of‐Safety Estimates for Fry, Fingerling, and Juvenile Rainbow Trout

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