Nature of Aeromonas salmonicida Carriage on Asymptomatic Rainbow Trout Maintained in a Culture System with Recirculating Water and Fluidized Sand Biofilters

Abstract

An asymptomatic carrier population of rainbow trout Oncorhynchus mykiss was examined for Aeromonas salmonicida by primary dilution counts on Coomassie Brilliant Blue agar and also by streaking on bacteriological media after a 24–48-h pre-enrichment in tryptic soy broth. The pathogen was detected by primary dilution plate counts in 1 spleen, 15 gill, and 19 mucus samples of the 100 trout examined. Aerornonas samonicida was detected only after 48-h preenrichment in the one spleen that had already tested positive via primary dilution counts. The pathogen was not detected in kidney, liver, and intestinal samples. The occurrence of the pathogen in mucus and gills suggests a predominantly external nature of asymptomatic carriage of A. salmonicida within this population of fish. Repeated examination of fluidized biofilters and tank water showed that A. salmonicida did not become established in the recirculation system.     

Effects of Formalin and Chloramine-T Treatments on Oxygen Consumption of Juvenile Salmonids

Abstract

The effects of formalin and chloramine-T on oxygen consumption of juvenile brook trout Salvelinus fontinalis at low water temperature were studied with a flow-through respirometer. No changes were found in the oxygen consumption of these fish after exposure to formalin at 200 and 400 μL/L or to chloramine-T at 10 μL/L during 1-h flow-through treatments. Additionally, there was no evidence of chemical oxygen demand exerted by formalin at dose levels up to 1,600 μL/L or by chloramine-T at I0 μL/L. When juvenile rainbow trout Oncorhynchus mykiss were treated with formalin at 200 μL/L for 1 h in an aerated tank simulating a static bath treatment, sham-treated control tanks had a significantly greater maximum decline in dissolved oxygen than formal in-treated tanks. These studies suggest that posttreatment mortalities that occur after low-temperature bath treatments with these chemicals are not directly related to oxygen consumption.     

Host factors associated with the detection of Aeromonas salmonicida and Yersinia ruckeri in Ontario, Canada government fish hatcheries

This paper presents an epidemiological investigation of Ontario Ministry of Natural Resources Fish Health Laboratory data from 1981 to 1997, to determine whether fish species and age were associated with lot-level detection of Aeromonas salmonicida and Yersinia ruckeri in hatchery fish. In stepwise logistic regression, the species brook trout and back-cross (lake trout crossed with the hybrid “splake”) were more likely to test A. salmonicida-positive compared to all other species reared in the hatcheries. Similarly, the species brook trout was significantly more likely to test Y. ruckeri-positive compared to all other species. For both pathogens, the 1–5-month age group was associated significantly with detection. These findings suggest that purposive sampling of higher-risk fish lots could increase the likelihood of detecting both study pathogens.     

Infections of Edwardsiella tarda among Brook Trout in Quebec

Abstract

Acute bacterial septicemia is commonly diagnosed in brook trout Salvelinus fontinalis of Quebec, Canada. The agents most commonly isolated include Aeromonas salmonicida (furunculosis), Aeromonas hydrophila (motile aeromonad septicemia), and Pseudomonas species. Septicemia in brook trout caused by the gram-negative bacterium Edwardsiella tarda was diagnosed for the first time in the province of Quebec from two different fish farms producing stock for fee fishing establishments. Affected fish displayed nonspecific lesions associated with bacterial septicemia including hemorrhages on the gills and viscera and exophthalmia. Stress-associated immunosuppression due to an increase in summer water temperatures and lack of precipitation were considered as primary causes of these disease outbreaks.     

Experimental Treatment of Aeromonas salmonicida Infections with Enrofloxacin and Oxolinic Acid: Field Trails

Abstract

The antimicrobials enrofloxacin and oxolinic acid were evaluated under field conditions for treatment of clinical Aeromonas salmonicida infections in salmonids by feeding medicated diets. Treatment of Atlantic salmon Salmo salar with enrofloxacin or oxolinic acid at 5 mg/ kg per day for 5 d was not successful. Monitoring of enrofloxacin-medicated fish revealed low tissue and serum antimicrobial activities. Lack of efficacy in the Atlantic salmon trial may have been due to the low dose, lack of bioavailability of the drug, or lack of acceptance of the medicated ration. Treatment of hybrid brook trout Salvelinus fontinalis × lake trout S. namaycush was successful when enrofloxacin was used at 10 mg/kg per day for 10 d, but not when oxolinic acid was used at 5mg/kg per day for 10 d. Antimicrobial activity in tissues of enrofloxacin-medicated fish was elevated during the 10-d treatment period. No antimicrobial activity could be detected in muscle, skin, or liver of the enrofloxacin-medicated fish at 20 d after the last day of medication.     

Occurrence and Distribution of Aeromonas salmonicida Infections on Swedish Fish Farms, 1951–1987

Abstract

The occurrence of typical and atypical Aeromonas salmonicida infections on Swedish fish farms was surveyed, and the methods for controlling the disease are described here. This review is based on data for a period of 36 years from fish health control studies conducted by the National Veterinary Institute and the Salmon Research Institute. The epizootiology and routes of transmission of the pathogens are described, and policy and methods for disease control are discussed. The distribution of atypical A. salmonicida infections was entirely different from that of typical infections. There was also circumstantial evidence of different routes of transmission for typical and atypical A. salmonicida infections. Although subclinical carriers of atypical A. salmonicida occurred among Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss on fish farms, acute disease outbreaks were most frequent among Arctic char Salvelinus alpinus and brown trout Salmo trutta. On the other hand, acute outbreaks of typical A. salmonicida infections were frequent among Atlantic salmon and rainbow trout.     

Physiological and Immunological Effects of Adjuvanted Aeromonas salmonicida Vaccines on Juvenile Rainbow Trout

Abstract

The effects of injectable vaccines against Aeromonas salmonicida on oxygen consumption, growth, kidney lysozyme activity, and anti-A. salmonicida plasma antibody titers of juvenile rainbow trout Oncorhynchus mykiss were examined. The vaccines were A. salmonicida bacterin only, bacterin adjuvanted with levamisole, bacterin in emulsified oil, microencapsulated bacterin, microencapsulated bacterin with muramyl dipeptide, microencapsulated bacterin with β-1,3-glucan, and microencapsulated bacterin with Vibrio anguillarum lipopolysaccharide (LPS). The greatest and broadest ranges of responses were caused by the microencapsulated bacterin with V. anguillarum LPS. Oxygen consumption rates and specific growth rates were significantly higher over the course of 1 month among fish treated with the LPS vaccine. These fish also maintained a higher anti-A. salmonicida plasma antibody titer and kidney lysozyme activity for a substantially longer period than fish receiving the other treatments.     

Effect of Common Aquaculture Chemicals against Edwardsiella ictaluri and E. tarda

Abstract

Edwardsiellosis is an important bacterial infection of freshwater and marine fishes. Edwardsiella ictaluri causes enteric septicemia of catfish, and E. tarda causes emphysematous putrefactive disease of catfish and fish gangrene in various species; these diseases have considerable economic effects on the aquaculture industry. In addition, E. tarda is an important zoonotic pathogen. Thus, the reduction or elimination of these pathogens from an aquarium or aquaculture facility is imperative. This study examined a variety of commercially available chemicals for their ability to reduce or eliminate E. ictaluri and E. tarda from the aquatic environment. The various concentrations of chemicals were tested in vitro in microcentrifuge tubes with a known concentration of bacteria at room temperature. In this study, ethyl alcohol (30, 50, or 70%), benzyl-4-chlorophenol/phenylphenol (1%), sodium hypochlorite (50, 100, 200, or 50,000 mg/L), n-alkyl dimethyl benzyl ammonium chloride (1:256), povidone iodine (50 or 100 mg/L), glutaraldehyde (2%), and potassium peroxymonosulfate/sodium chloride (1%) were effective disinfectants, as each reduced or eliminated the number of detectable organisms within 1 min of contact time. However, neither Chloramine-T (15 mg/L) nor formalin (250 mg/L) substantially reduced bacterial counts even after 60 min of contact time.     

Effects of a Prophylactic Chloramine-T Treatment on Growth Performance and Condition Indices of Rainbow Trout

Abstract

Chloramine-T has been commonly used as a therapeutic agent for the treatment of bacterial gill disease and related phenomena in the salmonid aquaculture industry, and it is now commonly used as a prophylactic agent to prevent diseases in commercial salmonid hatcheries. Rainbow trout Oncorhynchus mykiss (average weight 98 g) were exposed to chloramine-T at 10 mg/L for 1 h twice weekly (a commonly used regime in the aquaculture industry) for 11 weeks. Fish were fed ad libitum without feed wastage throughout the 11 -week trial. Body weight, specific growth rate, feed conversion index, and appetite were assessed at the end of weeks 3, 6, 9, and 11. Chloramine-T treatment was not associated with either clinical disease or mortality. However, by the end of the trial, growth (based on body weight) of treated fish was significantly suppressed (δ = 7.3%) compared with control fish. Growth suppression was attributed to a significant reduction (δ = 9.3%) of feed conversion efficiency in treated fish. Based on specific growth rates, chloramine-T had an early negative effect on growth. The effect was diminished in later weeks (although not completely lost), which suggests some degree of compensation by the fish to the chemical agent.     

Rearing unit-level factors associated with bacterial gill disease treatment in two Ontario, Canada government salmonid hatcheries

Early-rearing salmonids in Ontario Ministry of Natural Resources (OMNR) fish hatcheries have been consistently affected by bacterial gill disease (BGD) (causative agent: Flavobacterium branchiophilum) for many years. Separate retrospective epidemiological investigations of BGD treatments at two OMNR fish hatcheries (Hatcheries A and B) for the 1999 production year were conducted using on-site hatchery records. Both investigations were carried out at the rearing unit-level, with early-rearing (<9 months of age) “tank-lot” as the unit of analysis to identify unique fish populations over time. Multivariable repeated measures logistic regression models were created for both hatchery datasets, controlling for lot-level and species effects. For Hatchery A, the species brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) were significantly associated with BGD treatment, as well as lower water exchange rate, and higher feeding and mortality percentages during the 2 weeks previous to BGD treatment. At Hatchery B, the species brook trout (S. fontinalis) and splake (Salvelinus namaycush × S. fontinalis) were significantly associated with BGD treatment, as well as lower individual fish weights and treatment for BGD during the previous week. These results emphasize the importance of water quality, feeding rate, fish size and prior mortality on the development of BGD. Significant hatchery and species effects were evident, and future observational research on BGD must account for these factors in their design and analysis.     

Cell-Surface-Associated Properties of Fish Pathogenic Bacteria

Abstract

Pathogenicity assays showed that 33 of 42 potentially pathogenic strains of bacteria tested were virulent to rainbow trout Oncorhynchus mykiss. Regardless of their degree of virulence to fish, strains of motile Aeromonas, A. salmonicida, and Vibrio anguillarum were moderately hydrophobic. Only 46 and 25°10 of the strains were able to hemagglutinate human and trout erythrocytes, respectively. Hydrophobicity and hemagglutination were practically absent in isolates of Yersinia ruckeri. A notable number of the strains positively adhered to salmonid (51%) and nonsalmonid (55%) fish cells. Whereas the treatment of the bacteria with proteinase K or trypsin did not decrease the hydrophobicity of the isolates, within motile Aeromonas and A. salmonicida species, strains with both protease-sensitive and -resistant hemagglutinating and adhesive abilities occurred. The effects of heat and sugars on hemagglutinating and hydrophobic properties varied within all bacterial groups. Although treatment of strains with D-mannose or L-fucose had distinct effects on adhesiveness according to the bacterial species and the cell system used, none of the heat-treated (80°C for 15 min) bacteria lost their capacity to adhere to cultured fish cells. The results showed that there was no direct relationship between any of the cell surface properties analyzed and the degree of virulence of the strains.     

Experimental Infection of Brook Trout with Infectious Hematopoietic Necrosis Virus Types 1 and 2

Abstract

Fry of brook trout Salvelinus fontinalis became infected and diseased after immersion exposure to infectious hematopoietic necrosis virus (IHNV), but a long-lasting IHNV carrier state was not induced. Duplicate groups of 100 fish were immersed for 6 h in baths containing a type 1 (Round Butte, RB) or a type 2 (Rangen, RA) IHNV isolate at a high or low dose. Brook trout mortalities induced by immersion in a bath of the RB or RA IHNV isolate at 10² plaque-forming units (pfu) per milliliter were equivalent (1 and 0%), but fish were more susceptible to infection with RA IHNV. Only the single dead fish in the RB group was infected, but 24% of the RAexposed fish were infected 1 week after exposure. At a dose of 10⁶ pfu/mL, exposure to RB IHNV resulted in a higher mortality (35%) and prevalence of infection (89% of live fish sampled at 1 week postexposure), but no infectious virus was detectable by 5 weeks after exposure. In contrast, RA IHNV exposure at a dose of 10⁴ pfu/mL resulted in only 5% mortality, and live fish killed at 1 week postexposure had a 22% prevalence of infection, but infectious virus was not detectable by week 3. Although brook trout have been previously considered to be resistant to IHNV, this study has shown that brook trout become diseased and die after exposure to a high dose of one type I IHNV isolate and can be infected after immersion exposure to even a low dose of type 1 or type 2 IHNV.     

鲤鱼杀鲑气单胞菌的分离鉴定及耐药性分析

为探究鲤鱼病原菌的生物学特性及耐药状况,从患病鲤鱼中分离到菌株CS126,对其进行形态学观察、生理生化性质测定、16SrDNA序列分析及药敏性测定。结果显示,菌株CS126为革兰氏阴性菌,不产生吲哚、不具有动力性,分解半乳糖、甘露醇,VP试验、赖氨酸脱羧酶、氧化酶阴性,七叶苷阳性。16SrDNA序列长度为1 459bp,GenBank登录号为KJ942580,与GenBank中杀鲑气单胞菌的相似性高达100%,进化树显示与杀鲑气单胞菌杀鲑亚种聚为一分支。这表明菌株CS126为杀鲑气单胞菌杀鲑亚种。该菌株对菌必治、诺氟沙星、氟苯尼考等8种药物高度敏感,但对氨苄西林、氨苄西林/舒巴坦、甲氧卞胺嘧啶和磺胺异恶唑等耐药。本试验结果为鱼类杀鲑气单胞菌的快速鉴定及鱼类疾病诊治提供参考依据。     

Early Life Stage Survival and Susceptibility of Brook Trout,Coho Salmon,Rainbow Trout,and Their Reciprocal Hybrids to Infectious Hematopoietic Necrosis Virus

Abstract

Triploid (heat-shocked) and diploid groups of rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, coho salmon Oncorhynchus kisutch, and reciprocal hybrids were produced, monitored for early life stage survival, and evaluated for susceptibility to infectious hematopoietic necrosis virus (IHNV). The female rainbow trout × male brook trout triploid hybrids had significantly greater (P < 0.01) survival than the diploid hybrids of this cross. The heat-shocked hybrid group of the female rainbow trout × male coho salmon also exhibited significantly greater survival to the eyed egg stage of development than the untreated group of this hybrid. Studies of the susceptibility of treatment groups to a 1990 IHNV isolate from the Hagerman Valley were conducted by using a standardized immersion exposure procedure at one or two different mean body weights. The diploid brook trout and coho salmon and two triploid hybrids (female rainbow trout × male brook trout or male coho salmon) were significantly less (P < 0.05) susceptible to IHNV than the pure-species diploid and triploid rainbow trout groups.     

Treatment of Ichthyophthiriasis in Rainbow Trout and Common Carp with Common and Alternative Therapeutics

Abstract

The goal of this laboratory study was to provide better knowledge about the treatment of ichthyophthiriasis (causative agent: Ichthyophthirius multifiliis, a ciliate bacteria) in rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio. The following questions were investigated: (1) the effectiveness of different chemicals (formalin, sodium chloride, hydrogen peroxide, Perotan, Virkon, Aquahumin, Baycox, and Ivomec) and at different concentrations and durations of application, (2) the number of treatments and the time intervals between treatments that were necessary to remove the parasite, and (3) how treatment effectiveness differed between the two species. The most effective treatment was a 37% stock solution of formalin at 110 μL/L of bath water for 1 h in rainbow trout and for 2 h in common carp. Aquahumin (150 μL/L for 2 h) was effective in slightly or moderately infected rainbow trout and at low water temperatures, but it was not effective for common carp. All other tested chemicals were ineffective. With formalin and Aquahumin, five treatments were necessary to remove I. multifiliis infestation. At 10 ± 1°C, the parasites were eradicated when the treatment was performed at 48-h intervals. At 18 ± 1°C the infestation was eliminated when treatment was performed at 24-h intervals but not at 48-h intervals. At 25 ± 1°C, treatment at 24-h intervals was ineffective; however, shorter intervals between treatments might improve treatment efficacy at this temperature. In contrast, the number of treatment repetitions played a minor role, and parasites were eliminated with five treatments in all experiments when the type of chemical and treatment interval were optimal.     

Journal of Aquatic Animal Health

Abstract

Channel catfish Icialurus punctatus ranging from 70 to 148 mm in total length were treated with formalin at a concentration of 25 μL/L for 4 h daily on four successive days each week over a 28-week period beginning in mid-September. Coefficients of condition (weight-tolength ratios) and histological examinations of gill tissues were used to evaluate health of fish exposed to formalin. Gill tissues of both formalin-treated and untreated fish showed effects typical of intensive culture, including hypertrophy, hyperplasia, and excess mucous secretion; no differences were found in gill morphometry between the two groups. Channel catfish periodically treated with formalin had a significantly higher coefficient of condition (P < 0.05) after 28 weeks and no indication of adverse effects attributable to formalin.     

Effects of Elevated Water Temperature and Immunosuppressant Treatment on Prevalence and Titer of Infectious Pancreatic Necrosis Virus in Naturally Infected Brook Trout

Abstract

Using fingerlings of brook trout Salvelinus fontinalis naturally infected with infectious pancreatic necrosis virus (IPNV), we demonstrated that elevated water temperature and treatment with the immunosuppressant triamcinolone acetonide (generic Kenalog®) significantly increases the titer of IPNV and probably also the prevalence of the infection. Stress-promoting treatments could potentially enhance the capability to detect various fish viral agents.     

Hatchery Efficacy Trials with Chloramine-T for Control of Bacterial Gill Disease

Abstract

Three hatchery trials were carried out to determine the efficacy of chloramine-T for the control of bacterial gill disease in rainbow trout Oncorhynchus mykiss, ranging in weight from 2.5 to 54 g. In each trial, we used a single flow-through treatment of 8.5 mg chloramine-T/L. The single treatment provided effective control in all three trials; however, results were best when treatment was begun in the early stages of an outbreak. A second or third treatment may be required if an outbreak is in an advanced stage or if fish are under stress.     

Wound Healing in Rainbow Trout following Surgical Site Preparation with a Povidone–Iodine Antiseptic

Abstract

We investigated the effects of preparing surgical incision sites with a topical antiseptic on wound healing and hematological response in rainbow trout Oncorhynchus mykiss. A povidone–iodine solution was applied both pre- and postsurgery to the incision sites on treated fish. Three-centimeter incisions in both treated (N = 9) and control (nontreated, N = 9) fish were closed with four nonabsorbable sutures sewn in a simple interrupted pattern. During the 42-d period of wound healing, there were no statistically significant changes in total erythrocyte counts (1.28 × 10⁶/mm³ ± 0.05 SE), in percentage of dividing erythrocytes (0.76% ± 0.07 SE), or in differential leukocyte counts. Postmortem, pathogenic bacterial infections in the kidney or spleen were not detected in any of the fish. There was no histological difference between control and treated incisions to show either beneficial or adverse tissue reactions to the topical antiseptic treatments. Blinded histological analysis revealed both treated and untreated incision sites healed within 42 d at the same rate. Therefore, preparation of the incision sites with a povidone–iodine antiseptic did not improve wound healing nor alter healing rate in rainbow trout under the conditions of this study.     

Efficacy of Hydrogen Peroxide to Control Parasitic Infestations on Hatchery-Reared Fish

Abstract

The efficacy of hydrogen peroxide to control external parasitic infestations on juvenile (10–33-g) rainbow trout Oncorhynchus mykiss was evaluated in three clinical field trials. Fish were exposed to hydrogen peroxide concentrations ranging from 0 to 560 mg/L for 30 min once every other day for a total of three treatments. Pre- and posttreatment skin scrapes and gill wet mounts of test fish were microscopically examined to identify and enumerate external parasites. Infestation severity was classified as nonexistent (0 organisms), low (1–10 organisms), moderate (11–20 organisms), or high (?21 organisms). In trial 1, pretreatment skin examinations revealed a severe infestation of the protozoan Ambiphrya on all fish examined. Posttreatment skin examinations conducted within 24 h of the last treatment indicated that all hydrogen peroxide treatments eliminated Ambiphrya, whereas control fish remained severely infested with the protozoan. In trial 2, pretreatment examinations of skin and gill samples indicated a high infestation of the trematode Gyrodactylus (skin) and the protozoan Trichodina (gills) on all fish. Posttreatment examinations conducted within 24 h of the last treatment indicated that Gyrodactylus was eliminated from the skin of all treated fish; however, the high infestation of Trichodina remained on the gills of the test fish. All control fish had high infestation levels of both parasites. A high infestation of Ambiphrya was found on the skin of test fish before treatment (trial 3). Posttreatment examinations conducted 14 d after the last treatment revealed that 56% of the fish were parasite free, whereas the remaining test fish had low infestation levels. Control fish remained severely infested with the parasite. Based on the efficacy data, all hydrogen peroxide treatment regimens were efficacious in the control of Ambiphrya and Gyrodactylus.