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.
Salmincola spp. are ectoparasites of major concern in wild and cultured salmonids. These parasites can cause respiratory distress and facilitate the entry of secondary pathogens. Of particular concern in the United States is S. californiensis, which can infest all Oncorhynchus spp. and is restricted largely to freshwater. Bath treatments with formalin and hydrogen peroxide have traditionally been used to control infestations of some parasitic copepods in cultured salmonids; however, these treatments can be difficult to apply, expensive, and stressful to fish and have not been shown to be effective against S. californiensis. A more effective and efficient treatment method needs to be developed. SLICE (0.2% emamectin benzoate [EB]) is a commercial in-feed treatment that has been shown to be effective for the control of sea lice infestations in seawater-reared farmed salmon and trout. We postulated that EB might also be efficacious for the control of parasitic copepods such as S. californiensis on freshwater-reared salmonids. Four trials were conducted to evaluate the effectiveness of SLICE-medicated feed administered at a target dosage of 50 µg EB·kg fish −1 ·d −1 for seven consecutive days to control infestations of S. californiensis on freshwater-reared rainbow trout. At the end of each trial (after either a 30-or 42-d posttreatment period), copepod prevalence in treated tanks was substantially reduced compared with the pretrial prevalence recorded in the reference populations. Additionally, a significant difference was detected in mean abundance between treated and control groups, with a 79-96% reduction in mean abundance among fish offered the EB-medicated feed. Based on the results of these trials, it was concluded that SLICE was efficacious in reducing infestations of S. californiensis on freshwater-reared rainbow trout.Copepods are the most prevalent of the parasitic crustaceans affecting a wide range of marine and freshwater finfish worldwide (Lester and Hayward 2006). Salmincola spp. are parasitic copepods of major concern in wild and cultured salmonids. It has been reported that the incidence and spread of these parasites can be exacerbated by degraded environmental conditions such as increased water temperature, high organic loading, low dissolved oxygen, and overcrowding (Sutherland and Wittrock 428 CONTROL OF Salmincola ON RAINBOW TROUT
AQUI-S 20E (10% eugenol) has been shown to be an effective fish sedative for freshwater finfish, but to be approved for use in the United States, the U.S. Food and Drug Administration must be provided with data demonstrating the product is safe to treated animals. Accordingly, we evaluated the safety of AQUI-S 20E when used to sedate Rainbow Trout Oncorhynchus mykiss, Yellow Perch Perca flavescens, and Channel Catfish Ictalurus punctatus. After identifying the highest effective concentrations likely to be used by fisheries biologists to sedate each species to handleable, replicate groups of fish were exposed to this intended concentration (1×) or a 50% higher eugenol concentration (1.5×) for periods of time adequate to effectively sedate 80% of fish to handleable (ET80) or for predetermined treatment periods exceeding the ET80. These predetermined treatment doses (40 and 60 mg eugenol/L for Rainbow Trout, 80 and 120 mg eugenol/L for Yellow Perch, and 100 and 150 mg eugenol/L for Channel Catfish), treatment periods (2.25-8.75 min for Rainbow Trout, 4.0-10.5 min for Yellow Perch, and 2.5-12.0 min for Channel Catfish; specific treatment periods depending on doses), and ET80 values were used to establish margins of safety for each species. An adequate margin of safety was defined as treatment periods ≥ 3-4 min longer than the 1× ET80 and ≥ 2-3 min longer than 1.5× ET80 after which fish survival was ≥ 95%. Based on survival, there was an adequate margin of safety associated with overexposing fish to AQUI-S 20E. Given the absence of biologically relevant effects of AQUI-S 20E exposure on tissue histology, there is no evidence to suggest that the survival-based margins of safety should be revised to be more conservative. Our results indicate there is an adequate margin of safety associated with the use of AQUI-S 20E to sedate freshwater fish to handleable.
Aquaflor (florfenicol, 50% with/without) is a potent, broad‐spectrum, antibacterial agent with bacteriostatic properties that are active against a variety of Gram‐positive and Gram‐negative bacteria. This product is approved by the U. S. Food and Drug Administration for use on several fish species to control mortality associated with a variety of diseases, including columnaris (causative agent, Flavobacterium columnare). Two independent experimental trials were separately conducted to evaluate the effectiveness of Aquaflor to control mortality associated with columnaris disease. Aquaflor was administered in feed at a targeted daily florfenicol dosage of 10 mg/kg of body weight for 10 consecutive days. Test species were fingerling Florida Largemouth Bass Micropterus salmoides floridanus and Bluegill Lepomis macrochirus. In each trial, 8 or 10 test tanks (4 or 5 treated, 4 or 5 control) were stocked with either approximately 473 bass (mean length = 6.4 mm; mean weight = 3.3 g) or 100 Bluegills (length = 10.3; weight = 25.2 g). At the end of the 14‐d posttreatment periods, mean cumulative mortality of bass in treated tanks was 5.7% per tank, which was significantly less than that in control tanks (12.0%). Mean cumulative mortality of Bluegills in treated tanks was 19% per tank, which was significantly less than that in control tanks (38%). Analysis of treated feed samples at the start of each trial verified the initial targeted dose of florfenicol was within 11% of the target dose for both bass and Bluegills. Based on these results, we concluded that Aquaflor‐medicated feed homogeneously mixed to provide florfenicol at a daily dose of10 mg/kg of body weight fed for 10 d was effective in controlling mortality in bass and Bluegill fingerlings, exposed to columnaris disease.
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