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

Abstract

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.

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

“…Survival of fingerling Channel Catfish Ictalurus punctatus with columnaris was significantly improved after being treated with HP at 50, 75, or 100 mg/L of water for 60 min/d on three alternate days, but these fish did not exhibit sensitivity to the higher doses (Rach et al 2003). Results from these studies suggest varying sensitivity to CLT and HP and a "Goldilocks paradigm" (i.e., CLT and HP doses that are too low or too high may yield less desirable results than one that is just right for the species or lifestage; Gaikowski et al 1999;Russo et al 2007;Gaikowski et al 2008;Bowker et al 2011).…”

Evaluation of Glutaraldehyde, Chloramine-T, Bronopol, Incimaxx Aquatic® and Hydrogen Peroxide as Biocides against Flavobacterium psychrophilum for Sanitization of Rainbow Trout Eyed Eggs

“…In this work, F. psychrophilum is much more resistant to chloramine-T since 300 ppm were needed to inhibit the bacterial growth and only severe chloramine-T treatments ranging from 400 to 1,200 ppm (for about 1 hr to 5 min, respectively) were bactericidal. Experiments performed to evaluated chloramine-T as possible candidate for approval for use to control mortality in freshwater-reared salmonids caused by bacterial gill disease have been shown that the fry and fingerlings viability was unaffected by exposure to concentrations less than 100 and 60 ppm, respectively [30]. Clearly, rainbow trout eggs are much more resistant to chloramine-T since none of the 20-min treatments of chloramine-T up to 1,200 ppm did reduce significantly the egg viability.…”

Determination of biosafety of the antibiotic oxytetracycline hydrochloride in Pangasianodon hypophthalmus

“…Following the USGS (2007) and FDA (2015) recommendations, a dose of 80 mg OTC kg −1 body wt of fish daily for 10 days was taken as the minimum dose of the drug for the establishment of its safety. So, for safety evaluation, the drug was administered at a maximum 10 times of the minimum treatment dose and three times of the treatment duration following Bowker et al (2011).…”