Search

Objective: The antiparasitic effect of peracetic acid (PAA) was evaluated against an infestation of the protozoan Trichodina spp. in naturally infected juvenile domestic seventh‐generation (F7) Striped Bass Morone saxatilis. Methods: Replicated treatments (n = 3) consisted of 1 and 2 mg/L PAA and a control; treatments were applied every other day for three treatments (30‐min static exposure). Infestation intensity was enumerated 20–24 h after each treatment by counting the number of Trichodina present in a wet mount of excised gill tissue. Result: Neither treatment rate was able to completely eradicate the parasite; however, 2 mg/L PAA resulted in a statistically significant reduction, which equated to 75% reduction of observed parasites. Conclusion: The 2‐mg/L PAA treatment regimen in the present study is proposed as a safe, environmentally friendly, and effective method for reducing the intensity of Trichodina infestations in Striped Bass. Impact statementDefining new treatment regimens for common aquaculture parasites is beneficial to the industry. Emphasis on environmentally friendly chemicals is also good for the industry. Improving animal welfare can be achieved by reducing parasites in fish. [ABSTRACT FROM AUTHOR]

Objective: An experiment was conducted to evaluate the effects of repeated copper sulfate (CuSO4) treatments on the growth and survival of juvenile Walleye Sander vitreus. Methods: Culture tanks were treated with 0 or 0.76 mg/L CuSO4 every other day for five exposures, then were not treated for 14 consecutive days; this regimen was repeated for a total of 10 exposures over the course of 50 days. Copper sulfate treatments had a half‐life of about 60 min. The study was conducted in flow‐through well water at ≈1.5 L/m and 23.8°C. Result: The resulting survival data for CuSO4 treated and nontreated fish was 96% and 85% survival, respectively, and not statically different. There was no difference in weight, with treated weighing 25.3 g compared to 25.2 g for nontreated control fish. Both groups had weight increases of over 400% during the study. Neither group differed in length, with treated fish reaching a mean length of 14.6 cm and nontreated reaching a mean length of 14.5 cm. Conclusion: The results indicate that repeated CuSO4 treatments had no effect on Walleye growth or survival. Impact statementCopper sulfate has a long history of use in aquaculture. While it is no secret that copper toxicity or other deleterious effects can happen, if used appropriately copper sulfate can be one of the most useful chemicals in aquaculture. [ABSTRACT FROM AUTHOR]

The use of copper sulfate pentahydrate (herein, designated CuSO4) for fungus control on fish embryos is extremely effective and economical for farmers in waters with moderate or high alkalinity/hardness; however, fry toxicity in low alkalinity/hardness waters is a concern. The present study determined the acute toxicity of CuSO4 to Largemouth Bass Micropterus salmoides in naturally soft water (42 mg/L alkalinity [as CaCO3], 41 mg/L hardness [as CaCO3]). Median lethal concentration (LC50) values at 24 h were 3.97 mg/L CuSO4 for yolk‐sac fry and 5.24 mg/L CuSO4 for swim‐up fry. Most importantly for farmers, the no observed effect concentration (NOEC; the highest concentration tested to not cause fry mortality) was 0.625 mg/L CuSO4 for both stages of fry. Regarding the safe use of CuSO4 for fungus control on Largemouth Bass embryos, this research was done to demonstrate CuSO4 toxicity to Largemouth Bass fry in soft water. [ABSTRACT FROM AUTHOR]

Flavobacterium covae (columnaris) is a microbial pathogen of the Golden Shiner (Notemigonus crysoleucas), a principal bait species. We investigated the effects of density and water temperature on the survival of fish subjected to a columnaris challenge and whether flow cytometry (FCM) could be a fast and reliable method to distinguish and enumerate F. covae populations from water and fish in experimental tanks. Juvenile Golden Shiners averaging 2.62 (±0.78 S.D.) g (negative for F. covae) were used in simultaneous trials at 22°C and 28°C in two ultra-low flow-through systems: each consisting of four treatments and five replicates per treatment. Treatments were fish stocked at either 600 fish/m3 or 2,400 fish/m3 and either challenged with F. covae or not; survival was observed for 48 h after challenge. Samples of water and fish tissue were obtained for FCM enumerations and validation by qPCR. No significant differences in survival were recorded between density treatments; however, high temperature and columnaris challenge treatments showed significantly higher mortality. Bacterial enumeration (number/mL) by FCM highly correlated with bacterial counts r = 0.81 (p = 0.001) in the water samples. Higher water temperatures may have increased columnaris infections and mortality in Golden Shiners. Flow cytometry is a reliable method of enumerating F. covae from experimental tank water samples. [ABSTRACT FROM AUTHOR]

Columnaris disease generates substantial losses of many freshwater fish species; one is the hybrid striped bass. The ubiquitous aquatic bacterium Flavobacterium columnare can be highly effective in biofilm formation on fish skin and gills. Previous research showed a difference between columnaris disease susceptibility of hybrid striped bass (Morone saxatilis × M. chrysops) and white bass (M. chrysops). To understand these differential susceptibilities and possible mucosal relationship, we assessed total bacterial growth and biofilm formation with mucus derived from each moronid parental species: white bass and striped bass (M. saxatilis). Differential susceptibility was confirmed of the other parent species, the striped bass (M. saxatilis). In addition to intraspecies investigations, individual hybrid striped bass mucosal affects were also studied for deferential responses to bacterial growth and biofilm formation. Species‐ and concentration‐dependent differences were detected in the total growth of the bacteria to host mucus. Our data suggest that bass mucus can significantly affect biofilm formation with the F. columnare isolate tested. There appears to be a correlation between the bacteria's response of growth and biofilms and bass species susceptibility. This study provides insight into our understanding of the host–pathogen interaction between F. columnare and moronids. [ABSTRACT FROM AUTHOR]

Columnaris disease is responsible for substantial losses throughout the production of many freshwater fish species. One of the ways in which the bacterium Flavobacterium columnare is so effective in initiating disease is through the formation of biofilms on fish skin and gills. To further explore the interaction between host factors and bacterial cells, we assayed the ability of vertebrate mucus to enhance F. columnare biofilm development. Different concentrations of catfish, tilapia and pig mucus (5–60 µg/ml) increased biofilm growth at varying degrees among F. columnare isolates. Our data suggest that vertebrate mucus acts as a signalling molecule for the development of F. columnare biofilms; however, there are clear disparities in how individual isolates respond to different mucus fractions to stimulate biofilms. The expression of iron acquisition genes among two genomovar II isolates showed that ferroxidase, TonB receptor and the siderophore synthetase gene were all significantly upregulated among F. columnare biofilms. Interestingly, the siderophore acetyltransferase gene was only shown to be significantly upregulated in one of the genomovar II isolates. This work provides insight into our understanding of the interaction between F. columnare and vertebrate mucus, which likely contributes to the growth of planktonic cells and the transition into biofilms. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare causes substantial losses among cultured finfish species. The Gram-negative bacterium is an opportunistic pathogen that manifests as biofilms on the host's mucosal surfaces as the disease progresses. We previously demonstrated that the dominant mucosal IgM antibody response to F. columnare is to the chaperone protein DnaK that is found in the extracellular fraction. To establish the efficacy of using recombinant protein technology to develop a new vaccine against columnaris disease, we are reporting on two consecutive years of vaccine trials using a recombinant F. columnare DnaK protein (rDnaK). In year one, three groups of channel catfish (n = 300) were immunized by bath immersion with a live attenuated F. columnare isolate, rDnaK or sham immunized. After 6 weeks, an F. columnare laboratory challenge showed a significant increase in survival (>30%) in both the live attenuated and rDnaK vaccines when compared to the non-immunized control. A rDnaK-specific ELISA revealed significant levels of mucosal IgM antibodies in the skin of catfish immunized with rDnaK at 4- and 6-weeks post immunization. In the second year, three groups of channel catfish (n = 300) were bath immunized with rDnaK alone or with rDnaK after a brief osmotic shock or sham immunized. After 6 weeks a laboratory challenge with F. columnare was conducted and showed a significant increase in survival in the rDnaK (> 25%) and in rDnaK with osmotic shock (>35%) groups when compared to the non-immunized control. The rDnaK-specific ELISA demonstrated significant levels of mucosal IgM antibodies in the skin of catfish groups immunized with rDnaK at 4- and 6-weeks post immunization. To further understand the processes which have conferred immune protection in the rDnaK group, we conducted RNA sequencing of skin samples from the non-immunized (n = 6) and rDnaK treated channel catfish at 1-week (n = 6) and 6 weeks (n = 6) post immunization. Significantly altered gene expression was identified and results will be discussed. Work to further enhance the catfish immune response to F. columnare rDnaK is underway as this protein remains a promising candidate for additional optimization and experimental trials in a production setting. [ABSTRACT FROM AUTHOR]

Columnaris disease is an important bacterial disease of commercially grown channel catfish, Ictalurus punctatus. Copper sulphate (CuSO4) has been shown to be therapeutic and prophylactic as a water treatment for columnaris disease. Copper is an essential dietary component in animal feeds and CuSO4 is typically included in base diets; a study was conducted to evaluate whether fish feed supplemented with additional CuSO4 at 0, 40 and 80 mg kg−1 of diet and fed at a daily rate of 3% body weight would affect survival to columnaris disease. Results indicate fish fed the copper-supplemented diet for 2 weeks significantly increased survival following F. columnare challenge. This increase appeared to be dose-dependent. The mean per cent survival (±SEM) for fish fed the base diet (unsupplemented) for 2 weeks and then challenged was 2.0% ± 1.1. Fish fed the base plus 40 mg CuSO4 kg−1 had a mean survival of 22.0% ± 11.0. Fish fed the base plus 80 mg CuSO4 kg−1 had a mean survival of 29.3% ± 13.4. The mean per cent survival for fish fed the base diet for 4 weeks and then challenged was 28.3% ± 9.0. Fish fed the base plus 40 mg CuSO4 kg−1 for 4 weeks had a mean survival of 12.5% ± 6.3. Fish fed the base plus 80 mg CuSO4 kg−1 for 4 weeks had a mean survival of 40.5% ± 8.1. There was a significant effect after 4 weeks with fish fed the base plus 80 mg CuSO4 kg−1 mg not with 40 mg kg−1. [ABSTRACT FROM AUTHOR]

An obstacle to the larval production of sunshine bass (female White BassMorone chrysops× male Striped BassM. saxatilis) is fungal growth on the eggs caused by the water mold,Saprolegniaspp. Copper sulfate (CuSO4) is commonly used for fungus control in troughs at catfish hatcheries, but the effectiveness in other fish-egg hatching systems is unknown. Because sunshine bass eggs begin hatching after 48 h, CuSO4treatments (0, 10, 20, and 40 mg/L) began the afternoon of spawning with a 10-min, aerated, static bath and were repeated the morning and afternoon of day 2; eggs were not treated after hatching began. An in vitro assay was developed for this treatment regimen that indicated maximum fungal inhibition was achieved with 20 mg/L CuSO4. In the effectiveness experiment in McDonald hatching jars (n= 3), fungus was severe in the untreated controls (27.7% survival), but very little fungus was present in treatments receiving 10 mg/L CuSO4(31.4% survival) or higher. The control was not significantly different from the 10-mg/L treatment. The highest survival was at 40 mg/L CuSO4(50.5% survival); however, the survival from the 20-mg/L CuSO4treatment (45.8%) was not significantly different from that in the 40-mg/L treatment and thus allows for a greater margin of safety. Fungus samples were identified asSaprolegnia feraxthrough genetic sequencing. Toxicity experiments on sunshine bass larvae indicated the 24- and 48-h LC50 values were 5.4 and 3.9 mg/L CuSO4, respectively; the no observed effect concentrations were 0.5 and 0.25 mg/L CuSO4, respectively. This study confirms that CuSO4can be an economical and valuable resource in hatchery management for the control of saprolegniasis on sunshine bass eggs in McDonald jars. Received September 25, 2015; accepted January 20, 2016 Published online June 15, 2016 [ABSTRACT FROM PUBLISHER]

Four studies were conducted to compare the effects of copper sulfate (CuSO4), when delivered in either a flow-through or a static system, on the survival of Golden ShinersNotemigonus crysoleucasand Fathead MinnowsPimephales promelasinfected withFlavobacterium columnare. The treatment regimens were administered to fish in well water and were based on the recommended treatment rate (1% of alkalinity). Golden Shiners (experiments 1 and 3) and Fathead Minnows (experiments 2 and 4) were treated separately. In experiments 1 and 2, the treatment rate was 2.0 mg/L CuSO4applied to a flow-through system daily for five consecutive days; control fish were untreated. Study durations were 7 d with the majority of the mortalities occurring in the first 5 d. Survival rates in the flow-through system were 77% and 69% for CuSO4-treated Golden Shiners and Fathead Minnows, respectively. Survival in both species was significantly different from that in their untreated control fish, which was 33% for Golden Shiners and 41% for Fathead Minnows. Static applications of CuSO4were investigated in experiments 3 and 4. Treatment doses were 0, 0.5, 1, 2, and 4 mg/L (approximately 0.0, 0.25, 0.5, 1, and 2 times the recommended rate). Survival of Fathead Minnows in this experiment was 10, 28, 52, 47, and 35% in the 0, 0.5, 1, 2, and 4 mg/L CuSO4treatments, respectively. The corresponding survival of Golden Shiners was 49, 50, 65, 75, and 60% in the 0, 0.5, 1, 2, and 4 mg/L CuSO4treatments, respectively. Received March 28, 2014; accepted August 2, 2014 [ABSTRACT FROM PUBLISHER]

A study was conducted to compare the effects of two chemical therapeutants on channel catfish (CCF)Ictalurus punctatusconcurrently infected withFlavobacterium columnareandIchthyobodo necator. Copper sulfate (CuSO4) and potassium permanganate (KMnO4) were investigated for their ability to reduce the bacterial load, parasite load, and subsequent mortality.Treatment rates of CuSO4or KMnO4were 2.1 mg/L and 3.0 mg/L, respectively, and were applied at 24 h intervals on three consecutive days and control fish were untreated. Fin and gill samples were taken on day 4 (24 h after the final treatment) and day 10 (one week after the final treatment) for quantification of parasite and bacterial load. The survival rate of CuSO4-treated fish (73.0 %) was significantly different from the untreated control fish (41.5%). KMnO4-treated fish was (53.6%) and not significantly different from untreated control or CuSO4-treated fish.I. necatorloads were significantly reduced by both CuSO4and KMnO4,but only CuSO4significantly reduced theF. columnareload. [ABSTRACT FROM PUBLISHER]

I chthyobodo necator is a single-celled biflagellate parasite, which in high density can cause significant mortality in young fish. Copper sulphate ( CuSO4), potassium permanganate ( KMnO4) and peracetic acid ( PAA) were evaluated for effectiveness against ichthyobodosis. Treatments were: untreated control, 2.1 mg L−1CuSO4, 3.0 mg L−1 KMnO4, 1.5 mg L−1 PAA and 3.0 mg L−1 PAA, and were applied to flow-through tanks on three consecutive days. The study was designed to simulate the flow-through systems utilized in the commercial rearing of juvenile channel catfish ( I ctalurus punctatus). Mortality was monitored daily to compare survival rate among treatments. Parasite intensity was assessed pre chemical exposure and 20-24 h after the third application to determine effectiveness of the treatment. An assessment was also done 7 days post application to investigate possible reoccurrence. Copper sulphate, KMnO4 and PAA (3.0 mg L−1) significantly reduced the infestation rate of I . necator. Copper sulphate significantly improved the survival of I . necator infested channel catfish after three flow-through applications compared with the untreated control. The 3.0 mg L−1 PAA resulted in significantly lower survival than the untreated control, the 1.5 mg L−1 PAA and the KMnO4 were not statistically different from the untreated control. [ABSTRACT FROM AUTHOR]

Columnaris disease is one of the most important bacterial diseases affecting Channel Catfish Ictalurus punctatus commercially grown in the USA. This disease can greatly diminish the profitability of aquaculture operations by large-scale mortality events, particularly in the fingerling production phase. Three experiments were conducted to evaluate the susceptibility of Channel Catfish fingerlings to columnaris disease when they were preexposed to copper sulfate (CuSO4). In experiment 1, fish were exposed for 24 h to 0, 1, 2, or 4 mg/L CuSO4 and were challenged immediately with Flavobacterium columnare, the etiological agent of columnaris disease. The resulting survival data indicated that fish preexposed to CuSO4 and then challenged exhibited significantly lower survival than did fish not exposed and then challenged. Experiment 2 was designed as above, except after the 24-h static exposure to CuSO4, fish were subjected to an additional 24 h in flow-through water prior to the challenge with F. columnare. In contrast to experiment 1, fish preexposed to CuSO4 and allowed an additional 24 h in flow-through water had a significantly higher survival rate than fish not exposed and then challenged. Experiment 3 evaluated the longevity of resistance to columnaris disease afforded by preexposure to CuSO4; in this experiment the remaining fish from experiment 2 were challenged 9 d after exposure to CuSO4. The increased survival rate of fish preexposed to CuSO4 was still significantly different, indicating the incurred resistance to F. columnare lasts for at least a week after exposure to CuSO4. [ABSTRACT FROM PUBLISHER]

As a synthetic androgen, 17α-methyltestosterone (17MT) is frequently used to redirect the course of sex differentiation by exposing the undifferentiated gonad to a sufficient dosage. This hormone has been widely accepted as a safe and effective treatment for sex reversal in many fish species, and it is administered to larval tilapia (3–12 d old) for ∼28 consecutive days to produce populations of >90% males. This study assessed the safety of 17MT-treated feed when administered to larval Nile TilapiaOreochromis niloticusat one, three, and five times (i.e., 1×, 3×, and 5×) the proposed dosage of 9 mg 17MT/kg fish daily for 28 consecutive days. Despite elevated total ammonia nitrogen levels measured during the last 5 d of the study, environmental conditions were acceptable for rearing tilapia. Fish fed aggressively regardless of the concentration of 17MT in the feed, behavior was considered normal with no dose-related differences detected, and no mortality was observed in the 3× treatment group. Fish that were treated with five times the proposed therapeutic dosage had significant pathological changes. Based on the results of this study, the 17MT margin of safety extends to at least 3×  (27 mg 17MT/kg fish daily) the proposed dosage of 9 mg 17MT/kg fish daily when administered in feed for 28 d to Nile Tilapia. Received October 8, 2012; accepted December 7, 2012 [ABSTRACT FROM AUTHOR]

The article focuses on a study which examined the effectiveness of bath treatments of formalin and copper sulfate on cultured white bass or Morone chrysops infected by Onchocleidus mimus and Ichthyphthirius multifiliis. The researchers conducted a statistical analysis using one-way analysis of variance (ANOVA) to analyze infection intensity and treatment effect after each exposure. It noes the percentage effectiveness (P. E.) and prevalence of Onchocleidus mimus in gill of white bass.

Commercial products containing peracetic acid ( PAA) are strong disinfectants with a wide spectrum of antimicrobial activity and have been suggested as potential therapeutic agents in aquaculture. The aim of this study was to compare the in vitro reduction of growth on two fish pathogens, Flavobacterium columnare and Saprolegnia parasitica, by seven commercial PAA-containing products. Flavobacterium columnare was exposed to 1, 2, 4, 6, 8 and 10 mg L−1 PAA and S. parasitica was exposed to 0.5, 1, 2, 4, 6, 8 and 10 mg L−1 PAA in petri dishes for 24 h incubation. The reduction of growth was measured in comparison to a PAA-free control. A reduction of the growth was observed for both pathogens with increasing PAA concentration. Hydrogen peroxide ( H2O2) possibly has a role in the effectiveness of the products, since products with lower PAA concentrations had a higher concentration of H2O2. The commercial products with a low concentration of PAA and a low PAA: H2O2-ratio were generally more effective against pathogens. The practical application of the products with low PAA concentration should be prioritized. [ABSTRACT FROM AUTHOR]

Copper sulfate (CuSO4) and potassium permanganate (KMnO4) were evaluated for their effectiveness to curtail mortality and decrease bacterial load in fish tissues and water in channel catfish Ictalurus punctatus infected with Flavobacterium columnare, the causative agent of columnaris. Fish (average size, 16.6 g and 13.7 cm) were obtained from a single culture tank undergoing an epizootic of columnaris and were stocked at a density of 30 fish per tank in each of 12 tanks. The study consisted of three treatments (n = 4 replicates per treatment): an untreated control group, a CuSO4-treated group, and a KMnO4-treated group. Treatment rates were 2.1 mg/L CuSO4 and 3.0 mg/L KMnO4 and were applied on three consecutive days at 24-h intervals. Caudal fin, gill, and liver samples were taken from one fish of each replication 24 h after the last treatment for analysis by quantitative real time PCR. A significant improvement in survival was noted among fish treated with CuSO4 (72.7%) compared with the control fish (38.5%) and the KMnO4-treated fish (52.2%). Survival of the KMnO4-treated fish was not significantly different from the control. Quantitative PCR indicated a significant reduction of bacteria in the water after the first and second treatments of both therapeutants; no difference was detected in fish tissues. Histological analysis of gill samples 24 h after the last treatment indicated that CuSO4-treated fish exhibited significantly less gill damage than untreated controls and there was no difference in KMnO4-treated fish. Copper sulfate therapy significantly improved survival, reduced the number of bacteria in the water, and reduced gill pathologies associated with F. columnare infection in channel catfish. Received August 23, 2011; accepted November 22, 2011 [ABSTRACT FROM AUTHOR]

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. Received September 30, 2010; accepted April 8, 2011 [ABSTRACT FROM AUTHOR]

Columnaris disease, caused by Flavobacterium columnare, severely impacts the production of freshwater finfish species. Therefore, efforts to better understand the biological processes of F. columnare, including the formation of biofilms and their contribution to disease, are ongoing. In this study, we incubated F. columnare cultures with channel catfish mucus and used high-throughput RNA sequencing to evaluate global changes in gene expression. Our data show that mucus activates in vitro biofilm formation. The analysis of F. columnare transcriptomes after the addition of mucus revealed significant differentially expressed genes (DEGs) between the planktonic and biofilm states. DEGs common among all biofilms were enriched for gene ontology groups including signal transduction, ligand binding and cellular homeostasis and are likely necessary for biofilm formation. Iron acquisition systems included TonB-dependent receptor and ferroxidase genes were expressed among all biofilms, while siderophore synthesis genes were only expressed in mucus-stimulated biofilms. The current analysis of F. columnare transcriptomes adds valuable information about the basic biological processes that occur during the planktonic and biofilm states. This work serves as a basis for future studies on understanding how biofilms are established and how they contribute to disease progression. [ABSTRACT FROM AUTHOR]

Flavobacterium covae is one of four Flavobacterium spp. that cause columnaris disease in teleost fish. Here, we report the draft genomes of two isolates, LSU-066-04 and LV-359-01, and their predicted virulence factors.

Hybrid striped bass (HSB) and white bass (WB) were evaluated for their susceptibility to Flavobacterium columnare, the causative agent of columnaris disease, in 3 fundamental studies. In the first experiment, we determined whether columnaris disease could be developed by experimental challenge in HSB. This challenge consisted of 3 levels of F. columnare (10, 30, and 60 ml volumes) determined to be 2.25 × 10(7), 6.75 × 10(7), and 1.35 × 10(8) CFU ml(-1), respectively. Each treatment group exhibited significantly different survival rates: 0, 3.3, and 13.3% in the 60, 30, and 10 ml groups, respectively. In Expt 2, using the 30 ml dose, both HSB and WB had a 0% survival rate, with WB taking significantly longer to reach 100% mortality. In Expt 3, using the 10 ml dose, no HSB survived, whereas 33% of WB survived (p < 0.0001). Compared to controls, HSB treated with 10 ml showed extensive gill damage at 24 h, which could have contributed to the higher mortality observed in HSB; in contrast, WB gills showed noticeably less damage. From these series of experiments, it is clear that HSB are more sensitive to F. columnare, having lower survival and more extensive histological damage compared to WB following challenge.

Ammonia concentrations in water can affect the severity of Flavobacterium columnare infections in fish. Two trials lasting 7 d each were conducted to determine the effect of a single immersion flush treatment of total ammonia nitrogen (TAN; 15 mg/L) on the survival of channel catfish Ictalurus punctatus infected with E columnare; the chemical was added while the water flowed continuously through the tanks. Both trials consisted of four treatments: (1) no ammonia exposure and no bacterial challenge (control), (2) ammonia exposure only, (3) bacterial challenge only, and (4) both ammonia exposure and bacterial challenge. Two hours after exposure to ammonia, the highest un-ionized ammonia level was 0.43 mg/L. The percent un-ionized ammonia is based on TAN, temperature, and pH. Caudal fins from three fish in each treatment were sampled at 24 h posttreatment to be analyzed by quantitative real-time polymerase chain reaction (qPCR). No significant difference in survival (mean +/- SE) was noted between the channel catfish in treatment 1 (95.2 +/- 1.2%) and those in treatment 2 (95.6 +/- 1.0%); however, survival in both treatments 1 and 2 differed significantly from that in treatments 3 (8.5 + 4.5%) and 4 (41.8 +/- 12.7%). Treatment 4 catfish had significantly higher survival than treatment 3 catfish. Quantitative PCR data showed that treatment 4 fish had significantly less F. columnare (7.6 x 10(5)) than did treatment 3 fish (1.2 x 10(7)), and treatment 2 fish (8.5 x 10(3)) had significantly less bacteria than did treatment 1 fish (6.9 x 10(4)), indicating that ammonia limited the F. columnare infection. The highest mean concentration of the bacteria (3.9 x 10(7)) was found on moribund fish. The ammonia concentrations tested did not negatively influence fish survival but interfered with the infection process. An in vitro assay was also conducted to evaluate the direct effects of ammonia on F columnare.

A simple and reproducible microdilution method was developed to test the susceptibility of the bacterium Flavobacterium columnare to antibiotics in vitro. The testing was conducted at 28 degrees C for 44-48 h at two dilutions of Mueller-Hinton broth (DMHB) using a standardized inoculum, a reference isolate of Escherichia coli ATCC25922 as a quality control organism, positive and negative control wells, and standardized custom-made microtiter plates. The E. coli ATCC25922 and F. columnare ATCC23463 (the species type strain) had significantly better growth in DMHB at 1:5 (4 g/L) than at 1:7 (3 g/L). The E. coli ATCC25922 was found to be acceptable as a reference isolate and produced minimum inhibitory concentration (MIC) values similar to those in the range published by the Clinical and Laboratory Standards Institute derived using standard Mueller-Hinton broth. The new method was used to determine the MIC of 23 F. columnare isolates (representing the three genotypes of the species) to enrofloxacin, ampicillin, oxytetracycline, erythromycin, florfenicol, flumequine, ormetoprim/sulfadimethoxine, and oxolinic acid.