Skin lesions and spring mortality events of smallmouth bass Micropterus dolomieu and selected other species were first noted in the South Branch of the Potomac River in 2002. Since that year morbidity and mortality have also been observed in the Shenandoah and Monocacy rivers. Despite much research, no single pathogen, parasite, or chemical cause for the lesions and mortality has been identified. Numerous parasites, most commonly trematode metacercariae and myxozoans; the bacterial pathogens Aeromonas hydrophila , Aeromonas salmonicida , and Flavobacterium columnare ; and largemouth bass virus have all been observed. None have been consistently isolated or observed at all sites, however, nor has any consistent microscopic pathology of the lesions been observed. A variety of histological changes associated with exposure to environmental contaminants or stressors, including intersex (testicular oocytes), high numbers of macrophage aggregates, oxidative damage, gill lesions, and epidermal papillomas, were observed. The findings indicate that selected sensitive species may be stressed by multiple factors and constantly close to the threshold between a sustainable (healthy) and nonsustainable (unhealthy) condition. Fish health is often used as an indicator of aquatic ecosystem health, and these findings raise concerns about environmental degradation within the Potomac River drainage. Unfortunately, while much information has been gained from the studies conducted to date, due to the multiple state jurisdictions involved, competing interests, and other issues, there has been no coordinated approach to identifying and mitigating the stressors. This synthesis emphasizes the need for multiyear, interdisciplinary, integrative research to identify the underlying stressors and possible management actions to enhance ecosystem health.

Eighty striped bass Morone saxatilis were obtained from Delaware Bay using commercial gill nets set adjacent to Woodland Beach (n = 70) and Bowers Beach (n = 10) in December 2003. Fish were examined for gross lesions. Total lengths (TLs) and eviscerated weights were determined to calculate condition factors (K). Portions of spleens were aseptically harvested for bacterial culture, and portions of spleens, kidneys (anterior and posterior), livers, and gonads were obtained for histological examination. The size distribution of the striped bass was relatively homogeneous; the mean TL was about 600 mm for all samples. Mean K exceeded 0.95 in all samples and was not significantly different (P > 0.05) among samples. Significant differences in mycobacterial infection prevalence (P < or = 0.05) were observed among samples; samples obtained at Woodland Beach (WB) on December 10 (53.8%, n = 13) and December 17 (7.1%, n = 42) exhibited the most striking differences in prevalence. Mycobacterial infection intensity ranged from 1 X 10(2) to 1 X 10(7) colony-forming units per gram of spleen. Acanthocephalan infection prevalence and intensity, non-acid-fast bacterial infection prevalence, and fish sex ratio were also significantly different among the samples (P < or = 0.05). Similar to the mycobacterial infections, differences in sex ratio, acanthocephalan infection, and non-acid-fast bacterial infection were observed between the WB samples taken on December 10 and 17. However, no significant associations (P > 0.05) were observed between sex ratio or these infections and mycobacterial infection. The differences in bacterial and parasite infection prevalence and intensity and fish sex ratio in some samples indicate that these fish had a different history and that the epizootiology of mycobacterial infection in striped bass from Delaware Bay may be relatively complex.

The genera Flavobacterium and Flexibacter contain bacterial pathogens that affect fish worldwide. Most of these organisms are ubiquitous with the aquatic environment and some are opportunistic in nature. They tend to infect fish stressed by mechanical or environmental insult (Shotts and Starliper 1999). The bacterial pathogen and its fish host are usually related less so by geography and more so by temperature. Those bacteria that infect salmonids will also infect non-salmonids or warmer water species if the pathogen can survive at warmer temperatures. Therefore, several of the most psychophilic species infect only salmonids (Wakabayashi 1993, Shotts and Starliper 1999). This chapter covers both the salmonid and non-salmonid infecting bacterial species within the genera Flavobacterium and Flexibacter.

Journal of Fish DiseasesVolume 24, Issue 1 p. 53-56 Isolation of Serratia liquefaciens as a pathogen of Arctic char, Salvelinus alpinus (L.) C E Starliper, C E Starliper USGS-BRD National Fish Health Research Laboratory, Kearneysville, West Virginia, USASearch for more papers by this author C E Starliper, C E Starliper USGS-BRD National Fish Health Research Laboratory, Kearneysville, West Virginia, USASearch for more papers by this author First published: 07 July 2008 https://doi.org/10.1046/j.1365-2761.2001.00266.xCitations: 7 Dr C E Starliper USGS-BRD National Fish Health Research Laboratory, 1700 Leetown Road, Kearneysville, West Virginia 25430, USA Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume24, Issue1January 2001Pages 53-56 RelatedInformation

A part of the conservation efforts of native freshwater bivalves is a relocation program whereby animals are collected and moved to a safe refuge for maintenance and propagation. With the rearing of two different hosts, mussels and fish, on the same facility there is a question of the possibility for contagion of pathogens. The studies presented here are part of a continuing effort to address the concerns of contagion. Freshwater bivalves collected throughout the 1997 season were cultured for fish pathogens. Counts of total bacteria on cytophaga medium ranged between 1.07 x 10(5) and 4.99 x 10(5) cfu/g of mussel soft tissues. The predominate groups of bacteria were motile Aeromonas spp. and Pseudomonas spp., both of which include members that are opportunistic pathogens to salmonid fishes. No primary fish pathogens were cultured; however, cells with correct morphology for Renibacterium salmoninarum, cause of bacterial kidney disease, were detected from mussel soft tissues in all six trials using the direct fluorescent antibody test. Groups of mussels were subjected to 24-h waterborne challenges using bacteria cultured from healthy fish. no mortality occurred to any of the animals. Another group exposed to the fish pathogen Aeromonas salmonicida also showed no effects of the challenge; however, susceptible fish became infected and died after the fish were added to cohabit with this group of mussels.

In response to interest in the culture of freshwater bivalves on refugia with salmonid fish, studies were initiated to examine the potential for bacterial pathogen contagion between the two hosts. Freshwater bivalves were collected from the Ohio River in November 1995 and June and September 1996. In all 190 animals were sampled, some from their native Ohio River water (day 0) and others after relocation to a different water supply. Sampling and bacterial isolation techniques are described. The mean total bacteria counts were about 1.6 x 10(5) CFU/g of bivalve soft tissue, and this remained relatively stable during the 30-day period, yet the distribution was dynamic. Flavobacterium columnare, a salmonid fish pathogen, was isolated from one Amblema plicata of a day 0 sample in June 1996 but not after relocation to a different water source.

Isolates of Aeromonas salmonicida, Edwardsiella ictaluri, and Escherichia coli 1898, from different hosts and geographical locations, displayed resistance to Romet, a potentiated sulphonamide. This resistance is encoded on a plasmid (similar to 55 kb) containing sulphonamide resistance genes, sul I or sul II as demonstrated by polymerase chain reaction (PCR) analysis. PCR products from either sul I(similar to 900 bp) or sul II (similar to 400 bp) were sequenced and compared with the National Institutes of Health GenBank database sequences for these genes. The results suggest common environmental sources of this resistance factor related to various bacterial species and geographical areas. Sul I PCR fragments from various species were identical. This consensus sequence was 99.8% similar to the GenBank sul I sequence. Sul II PCR fragments from various species were 95-100% similar, which was 98.5% similar to the GenBank sul II sequence. The above bacterial species possess nearly identical sul I and sul II gene fragments (>95% homology) to GenBank sul I and sul II sequences from a variety of bacterial species representing hosts and geographical locations other than those in the present study.

These studies were done to determine the prevalence of infection, over time, of progeny from a population of 1988 year class brook trout, Salvelinus fontinalis (Mitchill), that was asymptomatically infected with Renibacterium salmoninarum, the causative agent of bacterial kidney disease. This population and its progeny from the 1991 and 1992 spawnings were monitored for approximately 3 years for prevalence of R. salmoninarum and development of bacterial kidney disease. Ovarian fluid samples from the 1991 and 1992 spawnings, and from a 1993 spawning of the 1991 progeny, were analysed for R. salmoninarum by enzyme linked immunosorbent assay (ELISA) and the membrane filtration fluorescent antibody technique. Kidney and spleen tissues of the 1988 year class were assayed by ELISA following the 1992 spawning. The progeny of the 1991 and 1992 spawnings were followed for increased prevalence of R. salmoninarum by the ELISA. Kidney tissues were assayed and sampling began once the fish were large enough. Each population of progeny was sampled quarterly for one year. Overall, the progeny displayed decreasing prevalence of R. salmoninarum and all ovarian fluids of the 1991 progeny (in 1993) were negative. Brood fish and progeny remained asymptomatic during the course of the study.

The dot blot assay, modified and adapted for detection of antigens from Vibrio anguillarum in fish tissues, was specific for V. anguillarum and did not react with antigens of V. ordalii, Pseudomonas sp., or Yersinia ruckeri. The blot assay enabled detection of as little as 2.3 ng of a mixture of protein antigens obtained from cell-free extracts of V. anguillarum; it was about 100 times more sensitive than either the indirect fluorescent antibody technique or bacterial isolation for detecting V. anguillarum in fish tissues.

Kidney and spleen homogenates from each of 60 coho salmon (Oncorhynchus kisutch) and steelhead trout (Salmo gairdneri) were examined for detection of Renibacterium salmoninarum. The proportions of positives differed widely with the detection procedures used: in coho salmon, 5% were positive by the Gram-stain procedure, 10% by the direct fluorescent antibody test, 48% by bacteriological isolation, 65% by staphylococcal coagglutination, and 73% by counterimmunoelectrophoresis; in steelhead trout, 3% were positive by Gram-stain, 8.3% by fluorescent antibody, 17% by bacteriological isolation, and 67% by counterimmunoelectrophoresis. Renibacterium salmoninarum was not detected in either coho salmon or steelhead trout by immunodiffusion analysis.

Effective control of enteric redmouth disease was obtained during artificial infection of rainbow trout (Salmo gairdneri) and in natural outbreaks in rainbow trout and chinook salmon (Oncorhynchus tshawytscha) with a potentiated sulfonamide, Ro5-O037, a combination of five parts sulfadimethoxine and one part ormetoprim. Treatment was given at the rate of 50 mg/kg of fish for 5 d.Key words: potentiated sulfonamide, enteric redmouth, therapy, salmonids

ABSTRACTAn avirulent strain of Aeromonas salmonicida was shown to lack “A‐layer” protein exterior to the outer cell membrane, but was still immunogenic in fish. After bacteria were inactivated with chloroform, whole cells, soluble antigen and combined whole cell plus soluble antigen vaccines were prepared. Those brook trout (Salvelinus fontinalis) that were vaccinated by a 60‐second immersion in the combined whole cell plus soluble antigen vaccine were protected against experimental challenges. Further immersion vaccinations of Atlantic salmon (Salmo salar) in the combined vaccine indicated that protection conferred by immunization was highly significant, efficacious, and reproducible. In field situations, mortality in brown trout (S. trutta) immersion‐vaccinated in this preparation was 2.1% whereas that in control fish was 28.9% after natural challenge.

Replicate groups of brook trout (Salvelinus fontinalis) immunized by intraperitoneal injection of graded dilutions of an avirulent strain of Aeromonas salmonicida were protected from a virulent challenge. Mean mortality after challenge was 88% in control trout, 66% in trout immunized with 3 x 106 or 3 x 105 cells, and 39% in trout immunized with 3 x 104 to 3 x 10¹ cells. In brook trout challenged after immersion for 60 s in a culture containing 2.3 x 109 avirulent cells of A. salmonicida per milliliter, mortality was 44%, compared with 94% in controls. In Atlantic salmon (Salmo salar), similarly vaccinated by immersion, mortality was 12.5% after challenge compared with 87.5% in controls. In additional studies, mean mortality of Atlantic salmon vaccinated by immersion was 14%, whereas that of control salmon was 92%.

The dot blot assay, modified and adapted for detection of antigens from Vibrio anguillarum in fish tissues, was specific for V. anguillarum and did not react with antigens of V. ordalii, Pseudomonas sp., or Yersinia ruckeri. The blot assay enabled detection of as little as 2.3 ng of a mixture of protein antigens obtained from cell-free extracts of V. anguillarum; it was about 100 times more sensitive than either the indirect fluorescent antibody technique or bacterial isolation for detecting V. anguillarum in fish tissues.