We conducted a field trial to evaluate the effectiveness of Aquaflor (50% florfenicol) for controlling mortality associated with Streptococcus iniae in freshwater-reared subadult sunshine bass (female white bass Morone chrysops X male striped bass M. saxatilis). Bacterial samples collected from moribund fish representing a reference population were presumptively identified microbiologically and were later confirmed to be S. iniae by biochemical characterization and polymerase chain reaction. The trial comprised a 1-d acclimation period, 10-d treatment period, and 14-d posttreatment period. During the treatment period, Aquaflor-medicated feed was administered to treated tanks (N = 3) at a target dose of 10 mg of florfenicol x kg of fish(-1) x d(-1), and nonmedicated feed was administered to control tanks (N = 3). At the end of the posttreatment period, mean (+/- SD) cumulative mortality in treated tanks (9 +/- 11%) was significantly (P = 0.040) less than that in control tanks (52 +/- 13%). Analysis of medicated feed samples revealed that treated tanks had received an actual dose of 8.3 mg florfenicol x kg fish(-1) x d(-1) (83% of target). No florfenicol was detected in control feed samples. Although the actual florfenicol dose administered to treated tanks was less than the target dose, the trial was accepted by the U.S. Food and Drug Administration Center for Veterinary Medicine as demonstrating the efficacy of Aquaflor to control mortality associated with S. iniae in cultured sunshine bass populations.

Aquaflor (florfenicol, 50% type A medicated article) is a relatively new antibiotic used in U.S. aquaculture and has been widely accepted as a safe and effective therapeutant. Some peer-reviewed studies have suggested that 15 mg florfenicol (FFC)·kg −1 body weight (BW)·d −1 for 10 d controls mortality to a greater extent than 10 mg FFC·kg −1 BW·d −1 for 10 d. This study evaluated the safety of Aquaflor to sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) when administered in feed at 15 (1× the maximum proposed therapeutic dose), 45 (3×), and 75 (5×) mg FFC·kg −1 BW·d −1 for 20 d (2× the currently approved 10-d treatment duration). The medicated feed was top-coated with Aquaflor and fed at 2% BW·d −1 divided equally between the morning and afternoon feedings. Juvenile sunshine bass (13.6 ± 1.6 g [mean ± SD]) were stocked into 100-L flow-through tanks at 20 fish per tank. Diets were randomly assigned to three replicate tanks per treatment; fish in three additional nonstudy tanks were fed control diets and weighed weekly to calculate proper feeding quantities. Throughout the trial, water quality was maintained within ranges suitable for sunshine bass culture, fish behavior appeared normal, and all feed was readily and rapidly consumed. There were no mortalities and fish health evaluations revealed no chronic toxicity patterns. None of the histopathologies distinctive to the use of Aquaflor were observed. In conclusion, there is an adequate margin of safety associated with administering Aquaflor-medicated feed to fingerling sunshine bass at the proposed therapeutic treatment regimen of 15 mg FFC·kg −1 BW·d −1 for 10 d.

Aquaflor is an aquaculture feed premix containing 50% florfenicol and is approved for use in more than 50 countries to control mortality in a variety of cultured fishes caused by diseases associated with infectious bacterial pathogens. As part of an effort to expand the current approval in the United States, we conducted a study to evaluate the safety of Aquaflor to Yellow Perch Perca flavescens when administered in feed at 0× (0 mg/kg), 1× (15 mg/kg), 3× (45 mg/kg), or 5× (75 mg/kg) the proposed maximum therapeutic treatment dose of 15 mg florfenicol·kg fish−1·d−1 for 20 consecutive days, 2× the proposed therapeutic treatment duration of 10 consecutive days. Fingerling Yellow Perch (7.8 ± 1.6 cm and 5.0 ± 3.4 g; mean ± SD) were stocked into flow‐through test tanks at 15 fish per tank, and treatments were randomly assigned to tanks in triplicate. At the end of the 20‐d exposure period, mean cumulative mortality in the 0× and 3× groups (6.7% for both) was greater than that in the 1× and 5× groups (2.2% and 0.0%, respectively); however, differences among the groups were not significant (P = 0.3741). Throughout the study, general fish behavior was characterized as normal, and fish consumed virtually all feed offered. Fish health and histology assessments revealed no signs or lesions associated with toxicity of florfenicol. In conclusion, there is an adequate margin of safety associated with administering Aquaflor‐medicated feed to fingerling Yellow Perch at the proposed therapeutic treatment regimen of 15 mg florfenicol·kg fish−1·d−1 for 10 d.

SLICE (0.2% emamectin benzoate [EB]) is an in‐feed treatment that has been shown to be effective and safe for controlling infestations of several ectoparasitic crustacean copepods and branchiurans in a variety of seawater‐ and freshwater‐reared fishes. Although the safety of EB (in a pre‐SLICE formulation) for use with seawater‐reared Rainbow Trout Oncorhynchus mykiss has been demonstrated, the safety of SLICE for freshwater‐reared Rainbow Trout has not. Consequently, we conducted a trial to evaluate the safety of SLICE for freshwater‐reared Rainbow Trout when administered in feed at a dose of 0 (0×), 50 (1 × the maximum proposed therapeutic dose [1×]), 100 (2×), or 150 (3×) μg of EB·kg of fish body weight (BW)−1·d−1 for 14 d (2 × the proposed 7‐d treatment duration). Medicated feed was prepared by top‐coating commercially available feed with SLICE. Rainbow Trout fingerlings (mean TL ± SD = 7.4 ± 0.7 cm; mean weight ± SD = 4.4 ± 1.2 g) were stocked into 57‐L flow‐through tanks at 20 fish/tank. Diets were randomly assigned to four replicate tanks per treatment; fish in four additional, nontrial tanks were fed control diets and were weighed weekly to calculate the proper feeding quantities. Throughout the trial, water quality was maintained within ranges suitable for Rainbow Trout culture, fish were fed the assigned feeds at 4% BW/d divided equally between three feedings, and fish behavior was characterized as normal. Fish in the 0×, 1×, and 2× exposure groups consumed all of the offered feed at least 92% of the time, whereas fish in the 3× exposure group consumed all of the offered feed 75% of the time. No fish died, and gross and microscopic fish health evaluations revealed no chronic toxicity patterns. Based on these results, we conclude that there is an adequate margin of safety associated with administering SLICE‐medicated feed to fingerling Rainbow Trout at the proposed therapeutic treatment regimen of 50 μg EB·kg fish BW−1·d−1 for 7 d.

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.