Journal of Aquatic Animal Health: Guide for Authors 2014

Abstract

Brook trout Salvelinus fontinalis were treated with single 60-min static baths of 250 mg formalin/L, 3% NaCl, and 15 mg Chloramine-T/L to evaluate the efficacy of these compounds against external infections of Aeromonas salmonicida. Prevalence of A. salmonicida was significantly lower in brook trout treated with Chloramine-T than among those treated with formalin or salt. Further laboratory tests substantiated the therapeutic value of a single treatment of ChloramineT (15 mg/L) against A. salmonicida. In two experiments, viable counts of A. salmonicida in mucus did not vary among replicate groups of treated brook trout, but the counts for treated fish were significantly (P < 0.05) lower than those for untreated controls. In vitro tube dilution assays indicated that mean minimum inhibitory concentrations of Chloramine-T for 10 isolates of A. salmonicida were 9.0 mg/L for 1 h and 2.25 mg/L, for 24 h. In field trials at the White River National Fish Hatchery (Bethel, Vermont), the pathogen was detected principally as an external infection of juvenile Atlantic salmon Salmo solar maintained in two culture ponds. In one pond, the bacterium accounted for 100% of the total distribution of tnicroflora isolated from mucus. Seven days after treatment with Chloramine-T, A. sahnonicida accounted for 11% of the total bacterial counts identified from these fish. In the second pond, A. salmonicida composed 3% of the counts of bacteria isolated from the mucus of fish before treatment but was not isolated after treatment.     

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.     

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.     

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.     

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.     

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.     

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.     

Modulation of juvenile brook trout (Salvelinus fontinalis) cellular immune system after Aeromonas salmonicida challenge

In fish, the first line of defence against infectious microorganisms is based on non-specific cellular immune mechanisms (innate immunity). In this study, we measured the non-specific immune parameters (natural cytotoxic cells (NCC) activity, lymphoproliferation, percentage of phagocytosis and phagocytic activity) in brook trout (Salvelinus fontinalis) infected by a virulent strain of Aeromonas salmonicida. Eight days post-infection, the mortality of infected fish reached 70%. A transient immunostimulation of the NCC activity was noticed 24h post-infection, but there was no significant difference at 48 h. Then, infection of brook trout with A. salmonicida induced a biphasic immune response. At 24h post-infection, lymphoproliferation was drastically depressed but returned to control level at 96 h. A slight increase in the percentage of phagocytosis and the phagocytic activity was noticed throughout the experiment. Conversely the cell mortality was significantly higher in infected fish compared to control. The modulation of immunological parameters might reveal important clues on how innate immunity might protect fish from bacterial infections.     

Antibiotic Resistance of Aeromonas spp. Isolated from Tropical Fish Imported from Singapore

Abstract

To determine the scope of antibacterial resistance among Aeromonas spp., bacterial cultures were taken from a variety of tropical fish species imported from Singapore. The samples were plated on Rimler-Shotts medium for bacterial isolation and identified with both the API20E and Nonfermenter Test Strip systems. Aeromonas hydrophila, A. sobria, and A. caviae were identified in monomicrobic and concomitant infections. Following identification of bacterial isolates, 11 antimicrobials routinely used in the tropical fish industry and 1 new fluoroquinolone were tested for their effectiveness against Aeromonas spp. with the Kirby-Bauer disk-diffusion technique. Aeromonas sobria proved to be the most resistant, often showing susceptibility to only 3 of 12 test drugs. Aeromonas hydrophila was consistently the least resistant. Based on these results, antimicrobial resistance appears to be a rapidly emerging problem in the pet fish industry.     

Effects of Salinity on Yersinia ruckeri Infection of Rainbow Trout and Brown Trout

Abstract

Juvenile rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta acclimated to freshwater or salinities of 9.0‰ or less were exposed to Yersinia ruckeri, the bacterial pathogen that causes enteric redmouth disease (ERM). Both species of fish were kept in the same recirculating systems after bacterial exposure. Rainbow trout mortality was significantly (P < 0.05) different in each salinity: 96.5% in freshwater, 89.5% in water of 1.1‰ salinity, 81.3% in 3.0‰ salinity, and 75.0% in 9.0‰ salinity (model SE = 1.0). All deaths occurred between 3 and 12 d after exposure to Y. ruckeri. Only 2.3% of brown trout in all salinities died, and differences among treatments were not significant. For both fish species, Y. ruckeri was isolated from liver, spleen, and trunk kidney of fish dying during this experiment, and lesions of rainbow trout were consistent with ERM. Yersinia ruckeri was not isolated from brown trout surviving for 21 d after bacterial exposure but was isolated from 3 of 24 surviving rainbow trout; a polymerase chain reaction assay detected the DNA of Y. ruckeri in 3 additional rainbow trout survivors. Neither the lesions of fish with ERM nor the percentage of surviving fish subclinically infected with Y. ruckeri was affected by salinity. Bacterial growth in vitro was not affected by low (≤9.0‰) salinity; however, bacterial adhesion to polystyrene was significantly reduced as salinity increased. Although mortality caused by Y. ruckeri was significantly lower for rainbow trout in water with slightly increased salinity, none of the salinities tested was effective in preventing serious losses caused by this pathogen in recirculating systems.     

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.     

In Vitro Infection of Salmonid Epidermal Tissues by Infectious Hematopoietic Necrosis Virus and Viral Hemorrhagic Septicemia Virus

Abstract

The ability of two rhabdoviruses, infectious hematopoietic necrosis virus (IHNV) and viral hemorrhagic septicemia virus (VHSV), to infect fish skin was investigated by in vitro infection of excised tissues. Virus replication was determined by plaque assay of homogenized tissue extracts, and the virus antigen was detected by immunohistology of tissue sections. Gill, fin, and ventral abdominal skin tissues of rainbow trout Oncorhynchus mykiss that had been infected in vitro with a virulent strain of IHNV (193–110) produced substantial increases in virus titer within 24 h. Titers continued to increase up until day 3 of incubation; by this time, virus had increased 1,000-fold or more. This increase in IHNV titer occurred in epidermal tissues of fingerlings and of older fish. In another experiment, IHNV replicated in excised rainbow trout tissues whether the fish had been subject to prior infection with a virulent strain of IHNV (Western Regional Aquaculture Consortium isolate) or whether the fish had been infected previously with an attenuated strain of the virus (Nan Scott Lake, with 100 passes in culture). A virulent strain of VHSV (23/75) replicated effectively in excised gill tissues and epidermal tissues of rainbow trout and chinook salmon O. tshawytscha; however, the avirulent North American strain of VHSV (Makah) replicated poorly or not at all.     

Prevalence of Infectious Pancreatic Necrosis Virus on Salmonid Fish Farms in Spain

Abstract

In Spain, salmonid fish farming was commercially developed in the 1960s, and now there are 140 private farms that depend heavily on imported embryonate eggs. Infectious pancreatic necrosis was first clinically diagnosed in Spain in 1970, but the virus (IPNV) was not isolated and identified until 1980. Since that time, researchers have isolated IPNV from other samples in Spain. A diagnostic survey was conducted to determine how prevalent IPNV is on fish farms in Spain and whether the virus has been responsible for some of the major financial losses occurring every year on these farms. In total, 236 samplings of rainbow trout Oncorhynchus mykiss from 31 farms in eight hydrographic areas were done over a 3-year period. Infectious pancreatic necrosis virus was isolated in 94 cases, and serotyping of the viral strains revealed that 81% of these isolates were strain Sp and 19% were strain Ab. Neither IPNV strain VR-299 nor rhabdovirus (as infectious hematopoietic necrosis virus or viral hemorrhagic septicemia virus) was detected in any of the samples.     

DNA Vaccination of Rainbow Trout against Viral Hemorrhagic Septicemia Virus: A Dose–Response and Time–Course Study

Abstract

Viral hemorrhagic septicemia (VHS) in rainbow trout Oncorhynchus mykiss is caused by VHS virus (VHSV), which belongs to the rhabdovirus family. Among the different strategies for immunizing fish with a recombinant vaccine, genetic immunization has recently proven to be highly effective. To further investigate the potential for protecting fish against VHS by DNA vaccination, experiments were conducted to determine the amount of plasmid DNA needed for induction of protective immunity. The time to onset of immunity and the duration of protection following administration of a protective vaccine dose were also analyzed. The dose–response analysis revealed that significant protection of rainbow trout fingerlings was obtained following intramuscular injection of only 0.01 μg of plasmid DNA encoding the VHSV glycoprotein gene. In addition, higher doses of DNA induced immunity to a virus isolate serologically different from the isolate used for vaccine development. Following administration of 1 μg of a DNA vaccine, significant protection against VHS was observed in the fish as early as 8 d postvaccination. At 168 d postvaccination, the fish had increased in size by a factor of 10 and protection against a lethal dose of VHSV was still evident. The results confirm the great potential for DNA vaccination in inducing efficient immunoprophylaxis against viral diseases in aquacultured fish.     

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.     

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.     

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.     

Serological Evidence of Infectious Hematopoietic Necrosis in Rainbow Trout from a French Outbreak of Disease

Abstract

Following the detection of infectious hematopoietic necrosis virus (IHNV) in France in April 1987, a serological survey was conducted of the rainbow trout Oncorhynchus mykiss (formerly Salmo gairdneri) from an infected cultured stock previously known to be contaminated with viral hemorrhagic septicemia virus (VHSV) for 3 years. The work lasted from April to December 1987, at which time all the remaining fish were slaughtered. Serum samples were assayed by a plaque-reduction test and a simplified neutralization test that is more suitable for processing large numbers of serum samples. Such investigations revealed that IHNV neutralization by trout antibodies depended on trout complement, as did neutralization of VHSV. Incubation for 16 h at 4°C increased the sensitivity of the test compared to incubation for 1 h at 20°C. During the course of clinical IHN from April to June, young fish did not display any neutralizing activity, but in September, 29 of 50 of them exhibited significant anti-IHN neutralizing antibody titers ranging from 21 to over 160, and 18 of 46 of these same fingerlings did so in December. Similarly, fish that had undergone VHS infection in August began to develop anti-VHSV antibodies in December (5 of 50), demonstrating that one fish can harbor neutralizing antibodies to both IHNV and VHSV, and that these antibodies had required 14 weeks to appear under fish culture conditions at 10°C. As could be expected from seroneutralization tests, neutralizing antibodies to IHNV did not result in protection against VHS. Sera from 13 of 20 adult fish sampled in mid-June revealed neutralizing antibodies to IHNV, suggesting that they harbored the virus prior to the clinical infection that affected their progeny. Only two of the fish showed low anti-VHSV antibody titers. Similarly, neutralizing antibodies to IHNV were detected in 53 of 73 other adult fish sampled in late October, 10 months after they had spawned and 7 months after mortality had occurred among their progeny. Given the prevalence, level, and persistence of neutralizing antibody titers, the seroneutralization test would be worth investigating more thoroughly to define the conditions that could make it a reliable tool for checking the virus status of trout carriers.     

Histopathological findings in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with 3 different Aeromonas species

This study describes the macroscopic and microscopic lesions in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with genetically identified Aeromonas salmonicida, A. hydrophila, and A. veronii species. The genus Aeromonas includes bacteria that naturally inhabit both waterways and organisms. At least 27 Aeromonas species have been identified to date, some of which can cause significant economic losses in aquaculture. As up to 68.8% of Aeromonas isolates may be misidentified in routine biochemical and phenotypic tests, however, reported cases of Aeromonas infection in fish may be wrongly identified. Our findings confirmed that the 3 Aeromonas species studied are associated with septicemia and dermal lesions in rainbow trout.     

Communications: Agglutination of Salmonid Spermatozoa by Renibacterium salmoninarum

Abstract

Renibacterium salmoninarum (American Type Culture Collection: ATCC 33209) agglutinated spermatozoa of brook trout Salvelinus fontinalis, rainbow trout Oncorhynchus mykiss, chinook salmon O. tshawytscha, white sucker Catostomus commersoni, and goldfish Carassius auratus, but not that of walleye Stizostedion vitreum or bulls Bos taurus. When examined microscopically, the bacteria were seen to be binding to the tails but not the heads of the sperm. The sperm agglutinin may be the previously reported renibacterial hemagglutinin.