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USGS2010

Susceptibility of three stocks of pacific herring to viral hemorrhagic septicemia

Laboratory challenges using specific-pathogen-free Pacific herring Clupea pallasii from three distinct populations indicated that stock origin had no effect on susceptibility to viral hemorrhagic septicemia (VHS). All of the populations were highly susceptible to the disease upon initial exposure, with significantly greater cumulative mortalities occurring in the exposed treatment groups (56.3-64.3%) than in the unexposed control groups (0.8-9.0%). Interstock differences in cumulative mortality were not significant. The virus loads in the tissues of fish experiencing mortality were 10-10,000 times higher during the acute phase of the epizootics (day 13 postexposure) than during the recovery phase (days 30-42). Survivors of the epizootics were refractory to subsequent VHS, with reexposure of VHS survivors resulting in significantly less cumulative mortality (1.2-4.0%) than among positive controls (38.1-64.4%); interstock differences in susceptibility did not occur after reexposure. These results indicate that data from experiments designed to understand the ecology of VHS virus in a given stock of Pacific herring are broadly applicable to stocks throughout the northeastern Pacific.

Journal of Aquatic Animal Health↗

USGS1977

Residues of organochlorines and heavy metals in tissues and eggs of brown pelicans, 1969-73

Shells of brown pelican (Pelecanus occidentalis) eggs collected in South Carolina from 1969 through 1973 were significantly thinner than shells of those collected before 1947. Residues of 10 organochlorine pollutants and 10 heavy metals were found in these eggs. Total organochlorine residues were apparently magnified 23 times from fish to pelican eggs, but interpretation of biomagnification was complicated by the migratory habits of both the pelicans and their chief prey fish. Residues of organochlorine pollutants and heavy metals were also found in tissues of brown pelicans. Dieldrin was probably involved in the death of a pelican that exhibited myocardial necrosis. Other pelicans died from gunshot wounds, various diseases, or unknown causes. From 1969 through 1973, there was a significant decline in residues of p-p'-DDE, p-p'-TDE, p-p'DDT, and dieldrin in eggs of the brown pelican in South Carolina, but the rate of decline was different for each pollutant. PCB's peaked in 1972 and then declined in 1973 to the lowest level in 5 years. In 1973, the first time in many years, South Carolina brown pelicans reproduced very well. The excellent reproductivity seemed related to lowered organochlorine residues and favorable tides, weather, and food supply.

Pesticides Monitoring Journal↗

USGS2007

Improved husbandry to control an outbreak of rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum

Case Description - A cohort of 35,200, 13-week-old, female rainbow trout at a fish farm was evaluated because of a 2-week history of anorexia and lethargy and a mortality rate of approximately 100 fish/d. Clinical Findings - Affected fish were lethargic and thin and had disequilibrium, bilateral exophthalmia, pale red gills and kidneys, red-tinged coelomic fluid, and pale brown livers. Some fish were differentially pigmented bilaterally. The presumptive diagnosis was bacterial or viral septicemia. The definitive diagnosis was rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum. Treatment and Outcome - A strategy for controlling the outbreak based on reducing pathogen numbers in affected tanks and reducing pathogen spread among tanks was developed. The option of treating with antimicrobial-medicated feed was discussed with the farmer, but was declined. After changes were made, mortality rate declined quickly, with no more deaths within 10 days after the initial farm visit. Clinical Relevance - Bacterial coldwater disease is the most common manifestation of infection with F psychrophilum in fingerling and adult rainbow trout. However, the organism can also cause rainbow trout fry syndrome. This condition should be included on a list of differential diagnoses for septicemia in hatchery-reared rainbow trout fry.

Journal of the American Veterinary Medical Associa↗

USGS2004

Differential propagation of the metazoan parasite Myxobolus cerebralis by Limnodrilus hoffmeisteri, Ilyodrilus templetoni, and genetically distinct strains of Tubifex tubifex

Whirling disease, caused by the parasite Myxobolus cerebralis, has infected rainbow trout (Oncorhynchus mykiss) and other salmonid fish in the western United States, often with devastating results to native populations but without a discernible spatial pattern. The parasite develops in a complex 2-host system in which the aquatic oligochaete Tubifex tubifex is an obligate host. Because substantial differences in whirling disease severity in different areas of North America did not seem explainable by environmental factors or features of the parasite or its fish host, we sought to determine whether ecological or genetic variation within oligochaete host populations may be responsible. We found large differences in compatibility between the parasite and various laboratory strains of T. tubifex that were established from geographic regions with different whirling disease histories. Moreover, 2 closely related species of tubificids, Limnodrilus hqffmeisteri and Ilyodrilus templetoni, which occur naturally in mixed species assemblages with T. tubifex, were incompatible with M. cerebralis. Virulence of the parasite was directly correlated with the numbers of triactinomyxon spores that developed within each strain of T. tubifex. Thus, the level of virulence was directly related to the compatibility between the host strain and the parasite. Genetic analyses revealed relationships that were in agreement with the level of parasite production. Differences in compatibilities between oligochaetes and M. cerebralis may contribute to the spatial variance in the severity of the disease among salmonid populations. ?? American Society of Parasitologists 2004.

Journal of Parasitology↗

USGS2014

Book review: Fowler's zoo and wild animal medicine (volume 8)

In the eighth volume of Fowler's Zoo and Wild Animal Medicine , the editors have returned to the original, comprehensive, taxa-based format last used in the fifth volume that was released in 2003. The book consists of 82 chapters, divided into taxonomic classes that include amphibians, reptiles, birds, and mammals, and a general topics section. The editors deliberately selected new senior authors who are expert veterinary advisors for the various taxa. This international assemblage of authors is impressive, although the book would have benefited from a greater diversity of disciplinary expertise. Synthesis of the large and expanding body of knowledge about zoo and wild animal medicine is a Sisyphean task, but one that the editors have accomplished well. The chapters were well written and are beautifully illustrated with high-quality images and generally well referenced. Much of the information is summarized in tabular format, which I found both a blessing and a curse. Tabulation of hematologic variables and anesthetic doses is helpful; however, tabulation of information regarding infectious and parasitic diseases results in a loss of detail. For example, methods of diagnosis for some diseases are omitted from some tables. The need for succinctness results in trade-offs, and statements such as “ Batrachochytrium dendrobatidis … is one of the most well described pathogens of anurans” with no further information leaves readers unsated. In addition, the book does not have any chapters on fish or invertebrates, which are notable omissions given the importance of these species. Those quibbles aside, this is a must-have book for all zoo and wild animal medicine students and practitioners. However, perhaps it is time to recognize that, during the 36 years since the first volume was published, this discipline has become too large to be contained in 1 book. This is largely because of the success of this book series, and it is a nice problem to have. Review info: Fowler's Zoo and Wild Animal Medicine (Volume 8). By R. Eric Miller & Murray E. Fowler, 2015. ISBN 978-1455773978, 773 pp.

Journal of the American Veterinary Medical Associa↗

USGS1997

Differences in detection of Aeromonas salmonicida in covertly infected salmonid fishes by the stress-inducible furunculosis test and culture-based assays

Accurate detection of Aeromonas salmonicida subsp. salmonicida (the cause of furunculosis disease) in covertly infected salmonids is difficult and is a cause of concern for those involved in fish health inspection and resource management programs. In this study, we examined populations of brook trout Salvelinus fontinalis , Atlantic salmon Salmo salar , and lake trout Salvelinus namaycush that previously sustained natural episodes of furunculosis. Consequently, the sampled fish were presumed to harbor latent infections. Mucus, gill, liver, kidney, heart, spleen, and intestine samples ( N = 100 fish per group sampled) were processed and examined by (1) direct dilution counts and (2) quadrant streaking after a 48‐h pre‐enrichment in trypticase soy broth (TSB). Another subsample of fish from each group was then subjected to stress‐inducible furunculosis tests. Stress tests detected A. salmonicida in three of four groups of fish that were examined whereas the pathogen was detected in only two of the groups analyzed with culture‐based assays. Although pre‐enrichment in TSB enhanced detection within internal sampling sites including the liver, heart, spleen, and kidney, enrichment did not enhance detection from mucus, gill, or intestinal samples.

Journal of Aquatic Animal Health↗

USGS2020

Liquid chromatographic determination of chloramine-T and its primary degradation product, p-toluenesulfonamide, in water

N -sodium- N -chloro-ρ-toiuenesulfonamide (chloramine-T) effectively controls bacterial gill disease (BGD) in cultured fishes. BGD, a common disease of hatchery-reared salmonids, causes more fish losses than any other disease among these species. This study describes a liquid chromatographic (LC) method that is capable of direct, simultaneous analysis of chloramine-T and its primary degradation product, ρ-toluenesulfonamide (ρ-TSA), in water. The procedure involves reversed-phase (C 18 ) LC analysis with ion suppression, using 0.01 M phosphate buffer at pH 3. The mobile phase is phosphate buffer-acetonitrile (60 + 40) at 1 mL/min. Both chemicals can be detected with a UV spectrophotometer at 229 nm; the method is linear up to 40 mg chloramine-T or ρ-TSA/L. Mean recoveries were 96.4 ± 6.1% for water samples fortified with 0.03 mg chloramine-T/L and 95.3 ± 4.6% for water samples fortified with 0.005 mg ρ-TSA/L. Limits of detection without sample enrichment for chloramine-T and ρ-TSA are 0.01 mg/L and 0.001 mg/L, respectively.

Journal of AOAC International↗

USGS2008

Decreased mortality of lake michigan chinook salmon after bacterial kidney disease challenge: Evidence for pathogen-driven selection?

In the late 1960s, Chinook salmon Oncorhynchus tshawytscha from the Green River, Washington, were successfully introduced into Lake Michigan. During spring from1988 to 1992, large fish die-offs affecting Chinook salmon occurred in the lake. Multiple ecological factors probably contributed to the severity of the fish kills, but the only disease agent found regularly was Renibacterium salmoninarum, the causative agent of bacterial kidney disease. in this study, survival after challenge by R. salmoninarum was compared between two Chinook salmon stocks: a Lake Michigan stock from Wisconsin (WI) and the progenitor stock from the Green River. We found that the WI stock had significantly greater survival than the Green River stock. Next, the WI and Green River stocks were exposed to the marine pathogen Listonella anguillarum (formerly Vibrio anguillarum), one of the causative agents of vibriosis; survival after this challenge was significantly poorer for the WI stock than for the Green River stock. A close genetic relationship between the Green River and WI stocks was confirmed by analyzing 13 microsatellite loci. These results collectively suggest that disease susceptibility of Lake Michigan Chinook salmon has diverged from that of the source population, possibly in response to pathogen-driven selection. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗

USGS2009

Differential virulence mechanisms of infectious hematopoietic necrosis virus in rainbow trout (Oncorhynchus mykiss) include host entry and virus replication kinetics

Host specificity is a phenomenon exhibited by all viruses. For the fish rhabdovirus infectious hematopoietic necrosis virus (IHNV), differential specificity of virus strains from the U and M genogroups has been established both in the field and in experimental challenges. In rainbow trout (Oncorhynchus mykiss), M IHNV strains are consistently more prevalent and more virulent than U IHNV. The basis of the differential ability of these two IHNV genogroups to cause disease in rainbow trout was investigated in live infection challenges with representative U and M IHNV strains. When IHNV was delivered by intraperitoneal injection, the mortality caused by U IHNV increased, indicating that the low virulence of U IHNV is partly due to inefficiency in entering the trout host. Analyses of in vivo replication showed that U IHNV consistently had lower prevalence and lower viral load than M IHNV during the course of infection. In analyses of the host immune response, M IHNV-infected fish consistently had higher and longer expression of innate immune-related genes such as Mx-1. This suggests that the higher virulence of M IHNV is not due to suppression of the immune response in rainbow trout. Taken together, the results support a kinetics hypothesis wherein faster replication enables M IHNV to rapidly achieve a threshold level of virus necessary to override the strong host innate immune response. ?? 2009 SGM.

Journal of General Virology↗

USGS2003

Review of techniques to prevent introduction of zebra mussels (Dreissena polymorpha) during native mussel (Unionoidea) conservation activities

Because of the declines in diversity and abundance of native freshwater mussels (superfamily Unionoidea), and the potential decimation of populations of native mussels resulting from the rapid spread of the exotic zebra mussel Dreissena polymorpha, management options to eliminate or reduce the threat of the zebra mussel are needed. Relocating native mussels to refugia (artificial and natural) has been proposed to mitigate the threat of zebra mussels to native species. Relocation of native mussels to refugia such as fish hatchery facilities or natural habitats within their historic range. Which are unlikely to be infested by zebra mussels, necessitates that protocols be developed to prevent the inadvertent introduction of zebra mussels. Several recent studies have developed Such protocols, and have assessed their effectiveness on the health and survival of native mussels during subsequent relocation to various refugia. The purpose of this project is to synthesize and evaluate the current protocols and to develop a set of procedures that resource managers and researchers should consider before conducting conservation activities in zebra mussel infested waters. We found that the existing protocols have many common points of concern, such as facility modification and suitability, zebra mussel risk assessment and management procedures, and health and disease management procedures. These conservation protocols may have broad applicability to other situations and locations. A summary and evaluation of the information in these main areas, along with recommended guidelines, are presented in this article.

Journal of Shellfish Research↗

USGS1997

Introgression and susceptibility to disease in a wild population of rainbow trout

We examined susceptibility of wild rainbow trout Oncorhynchus mykiss from the Metolius River, a tributary of the Deschutes River, Oregon, to genetic introgression and cerato myxosis as a result of stocking nonnative hatchery rainbow trout. Ceratomyxa shasta , an enzootic myxosporean parasite that can be lethal to nonnative hatchery rainbow trout, might have been limiting the interbreeding of hatchery and wild rainbow trout in the river. However, rainbow trout from the Metolius River had allozyme frequencies intermediate between those of wild and hatchery fish at LDH‐82* and sSOD‐1* , two diagnostic genetic loci that allow the inland subspecies of rainbow trout to be distinguished from hatchery strains of coastal origin. They also had notable frequencies of ADA‐1 *85 , an allele documented in hatchery rainbow trout but rarely seen in wild populations. We also found that rainbow trout in the Metolius River averaged 138.9 scales in the lateral series, intermediate between the counts for 9 coastal or nonnative hatchery populations, which always had fewer than 140 scales, and 10 inland populations, which always had more than 140 scales. Disease challenges revealed that rainbow trout from the Metolius River had much greater susceptibility to C. shasta than rainbow trout from the Deschutes River, which have genetic resistance to the lethal disease. Based on these data, we concluded that introgression with nonnative hatchery rainbow trout has reduced the abilities of wild rainbow trout in the Metolius River to survive when conditions for ceratomyxosis infection occur.

Oregon↗

USGS2007

Temperature-mediated differences in bacterial kidney disease expression and survival in Renibacterium salmoninarum-challenged bull trout and other salmonids

Resource managers considering restoration and reconnection of watersheds to protect and enhance threatened populations of bull trout Salvelinus confluentus have little information about the consequences of bacterial kidney disease (BKD) caused by Renibacterium salmoninarum. To better understand the response of bull trout to R. salmoninarum challenge, we conducted several laboratory experiments at two water temperatures. The extent, severity, and lethality of BKD in bull trout were compared with those of similarly challenged lake trout S. namaycush, Arctic char S. alpinus, Chinook salmon Oncorhynchus tshawytscha, and rainbow trout O. mykiss. The lethal dose of bacterial cells necessary to induce 50% mortality (LD50) was 10-fold lower at the 15??C challenge than at the 9??C challenge. Of the species tested, bull trout were relatively resistant to BKD, Arctic char were the most susceptible among Salvelinus species, and Chinook salmon were the most susceptible among Oncorhynchus species tested. Mean time to death was more rapid for all fish tested at 15??C than for fish challenged at 9??C. These results suggest that infection of bull trout with BKD likely poses a low risk to successful restoration of threatened populations. ?? Copyright by the American Fisheries Society 2007.

North American Journal of Fisheries Management↗

USGS2012

Costs of living for juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in an increasingly warming and invaded world

Rapid environmental change in freshwater ecosystems has created a need to understand the interactive effects of multiple stressors, with temperature and invasive predators identified as key threats to imperiled fish species. We tested the separate and interactive effects of water temperature and predation by non-native smallmouth bass ( Micropterus dolomieu ) on the lethal (mortality) and sublethal (behavior, physiology, and growth) effects for juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in seminatural stream channel experiments. Over 48 h trials, there was no difference in direct predation with warmer temperatures, but significant interactive effects on sublethal responses of juvenile salmon. Warmer temperatures resulted in significantly stronger and more variable antipredator responses (surface shoaling and swimming activity), while physiological indicators (plasma glucose, plasma cortisol) suggested suppression of physiological mechanisms in response to the combined stressors. These patterns corresponded with additive negative growth in predation, temperature, and combined treatments. Our results suggest that chronic increases in temperature may not increase direct predation over short periods, but can result in significant sublethal costs with negative implications for long-term development, disease resistance, and subsequent size-selective mortality of Pacific salmon.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1956

Histopathology of kidney disease in fish

Kidney disease is one of the most puzzling fish diseases known to exist in the United States. In less than Io years it has invaded the Pacific Northwest, exacting a heavy toll of hatchery salmon. Its first appearance apparently was in Massachusetts where Belding and Merrill' described a disease similar to that now seen on the Pacific Coast. In I946 it was diagnosed in Washington2 and since that time has been observed in an ever increasing number of hatcheries. There are unpublished reports of the same or similar diseases in both California and Washington in the early I93o's.3 The latest outbreaks occurred in the Federal hatcheries at Berlin, New Hampshire, and Cortland, New York, in brook, brown, and rainbow trout.4 There is evidence to indicate that the disease may be much more widely spread in New York State.5 The disease is especially dangerous since little is known of the origin or source of the causative agent. Indeed, the classification of the diplobacillus associated with kidney disease is still uncertain. Thus, with our present knowledge, it is difficult or impossible to eradicate the malady from an infected hatchery. Histopathologic studies were undertaken to clarify the pathology of the disease and to compare the eastern form with the western form.

American Journal of Pathology↗

USGS1994

Historical decline and current status of coho salmon in California

The southernmost populations of coho salmon Oncorhynchus kisutch occur in California where native coho stocks have declined or disappeared from all streams in which they were historically recorded. Coho salmon previously occurred in as many as 582 streams, from the Smith River near the Oregon border to the San Lorenzo River on the central coast. Information on the recent presence or absence of coho salmon was available for only 248 (43%) of those streams. Of these 248 streams, 54% still contained coho salmon and 46% did not. The farther south a stream is located, the more likely it is to have lost its coho salmon population. We estimate that the total number of adult coho salmon entering California streams in 1987-1991 averaged around 31,000 fish per year, with hatchery populations making up 57% of this total. Thus, about 13,000 nonhatchery coho salmon have been spawning in California streams each year since 1987, an estimate that includes naturalized stocks containing about 9,000 fish of recent hatchery ancestry. There are now probably less than 5,000 native coho salmon (with no known hatchery ancestry) spawning in California each year, many of them in populations of less than 100 individuals. Coho populations today are probably less than 6% of what they were in the 1940s, and there has been at least a 70% decline since the 1960s. There is every reason to believe that California coho populations, including hatchery stocks, will continue to decline. The reasons for the decline of coho salmon in California include: stream alterations brought about by poor land-use practices (especially those related to logging and urbanization) and by the effects of periodic floods and drought, the breakdown of genetic integrity of native stocks, introduced diseases, overharvest, and climatic change. We believe, that ,coho salmon in California qualify for listing as a threatened species under state law, and certain populations may qualify for listing as threatened or endangered under federal law.

California↗

USGS1997

The North American strain of viral hemorrhagic septicemia virus is highly pathogenic for laboratory-reared Pacific herring ( Clupea pallasi )

Specific-pathogen-free Pacific herring Clupea pallasi were reared in the laboratory from eggs and then challenged at 5, 9, and 13 months of age by waterborne exposure to low (10 1.5–2.5 plaque-forming units [PFU] per milliliter), medium (10 3.5–4.5 PFU/mL), or high (10 5.5–6.5 PFU/mL) levels of a North American isolate of viral hemorrhagic septicemia virus (VHSV). The fish were extremely susceptible to the virus, showing clinical disease, mortality approaching 100%, and only a limited increase in resistance with age. Mortality began 4–6 d after exposure and peaked at approximately day 7 in fish exposed to high levels of virus. Whereas the mean time to death showed a significant dose response ( P < 0.001), the percent mortality and virus titers in dead fish were generally high in all groups regardless of initial challenge dose. External signs of disease were usually limited to 1–2-mm hemorrhagic areas on the lower jaw and isthmus and around the eye, but 2 of 130 infected fish exhibited extensive cutaneous hemorrhaging. Histopathologic examination of tissues from moribund fish sampled at 2–8 d after exposure revealed multifocal coagulative necrosis of hepatocytes, diffuse necrosis of interstitial hematopoietic tissues in the kidney, diffuse necrosis of the spleen, epidermis, and subcutis, and occasional necrosis of pancreatic acinar cells. Virus titers in tissues of experimentally infected herring were first detected 48 h after exposure and peaked 6-8 d after exposure at 10 7.7 PFU/g. Fish began shedding virus at 48 h after exposure with titers in the flow-through aquaria reaching 10 2.5 PFU/mL at 4–5 d after exposure, just before peak mortality. When the water flow was turned off for 3 h, titers in the water rose to 10 3.5 PFU/mL, and the amount of virus shed by infected fish (on average, greater than 10 6.5 PFU/h per fish) appeared sufficient to sustain a natural epizootic among schooling herring. Taken together, these data suggest that VHSV could be a significant limiting factor for populations of Pacific herring.

Journal of Aquatic Animal Health↗

USGS2020

Liquid chromatographic determination of oxytetracycline in edible fish fillets from six species of fish

The approved use of oxytetracycline (OTC) in U.S. aquaculture is limited to specific diseases in salmonids and channel catfish. OTC may also be effective in controlling diseases in other fish species important to public aquaculture, but before approved use of OTC can be augmented, an analytical method for determining OTC in fillet tissue from multiple species of fish will be required to support residue depletion studies. The objective of this study was to develop and validate a liquid chromatographic (LC) method that is accurate, precise, and sensitive for OTC in edible fillets from multiple species of fish. Homogenized fillet tissues from walleye, Atlantic salmon, striped bass, white sturgeon, rainbow trout, and channel catfish were fortified with OTC at nominal concentrations of 10, 20, 100,1000, and 5000 ng/g. In tissues fortified with OTC at 100,1000, and 5000 ng/g, mean recoveries ranged from 83 to 90%, and relative standard deviations (RSDs) ranged from 0.9 to 5.8%. In all other tissues, mean recoveries ranged from 59 to 98%, and RSDs ranged from 3.3 to 20%. Method quantitation limits ranged from 6 to 22 ng/g for the 6 species. The LC parameters produced easily in teg ratable OTC peaks without coelution of endogenous compounds. The method is accurate, precise, and sensitive for OTC in fillet tissue from 6 species of fish from 5 phylogenetically diverse groups.

Journal of AOAC International↗

USGS1994

Loma sp. salmonids from the Eastern United States: Associated lesions rainbow trout

A microsporidian of the genus Loma was noted in the gills of rainbow trout Oncorhynchus mykiss from a state hatchery (Buford Trout Hatchery) in Georgia. Mortalities of varying severity occur at this hatchery every fall, and the microsporidian was noted during an experiment from August 1991 to January 1992 to determine the effects of water source on disease. Infections first appeared to be systemic in the October sample; xenomas were observed in heart, spleen, and peripheral vessel walls. The presence of unidentified intracellular material preceded the appearance of xenomas in all tissues, but whether this material was associated with inflammation or represented immature stages of the parasite has yet to be determined. These structures were also noted in the intestine and liver, although xenomas were not noted in these organs. Mature xenomas did not elicit an inflammatory response but appeared to be short-lived. When the xenoma wall ruptured and released spores, an inflammatory response was again observed. The prevalence and severity of the infection were determined in fish maintained in troughs with well water, Chattahoochee River water, or hatchery (treated river) water. The infection tended to be more prevalent and more severe in fish maintained in the hatchery or river water than in those maintained in the well water. Stress induced by poor water quality may increase mortality from this parasite. This report extends the range of Loma sp. into the eastern United States.

Journal of Aquatic Animal Health↗