Longevity of Ceratomyxa shasta and Parvicapsula minibicornis actinospore infectivity in the Klamath River

Infectious Ceratomyxa shasta and Parvicapsula minibicornis actinospores were present in Klamath River samples collected in April, May, and June 2005. Juvenile Chinook salmon Oncorhynchus tshawytscha exposed to river water maintained at the ambient Klamath River temperature for 0, 4, 24, 72, and 168 h (7 d) developed asymptomatic infections from both parasites. Elevated water temperature (18 degrees C) in June may have reduced actinospore viability, as both C. shasta and P. minibicornis infection markedly declined in fish exposed for over 72 h. As judged by the prevalence of infection for both parasites, the number of infectious actinospores tended to increase or remain steady through the spring. Ceratomyxa shasta infections were characterized by the presence of a few trophozoites within granulomatous foci in mesentery adipose tissue and were consistently observed outside of the intestine. Similarly, low numbers of P. minibicornis were observed in kidney glomeruli and tubules but were not associated with inflammation. Parvicapsula minibicornis DNA was consistently detected by quantitative real-time polymerase chain reaction in filtered water samples collected each month and from each time posttransfer. These data and the high prevalence of infection observed in the exposed fish indicate that P. minibicornis actinospores were at a relatively high concentration in the river during the spring. In contrast, C. shasta DNA was only detected in half of the water sample sets and its detection did not correspond well to C. shasta infectivity. An approximately threefold increase in river flow from the April to the May water collection was not associated with a decline in either the detection of actinospores (particularly for P. minibicornis) or the prevalence of infection for both parasites. Actinospores of these myxosporean parasites have the potential to infect salmonids for at least 7 d after release from the alternate polychaete host.     

Surveillance for Ceratomyxa shasta in the Puget Sound watershed, Washington

Discovery of fish exhibiting clinical signs of ceratomyxosis in Washington State prompted concern over the potential impact of the myxozoan parasite Ceratomyxa shasta on native stocks of steelhead Oncorhynchus mykiss (anadromous rainbow trout). To investigate these concerns, a survey of 16 freshwater systems within the Puget Sound watershed, including Lake Washington, was conducted by sentinel exposure of susceptible fish (cutthroat trout O. clarkii and rainbow trout). Fish were exposed for 7 d during September 2003 and May 2004 and then were returned to a holding facility for monitoring of disease signs. Mortality caused by the parasite occurred only in the exposure group held at the University of Washington Hatchery, which receives its water from Portage Bay of Lake Washington. Fish from all other sites were negative for C. shasta, both visually and by polymerase chain reaction (PCR) assay, except for a single fish held at the Tumwater Falls Hatchery in September 2003. A single deformed spore was detected in that fish, but infection could not be confirmed by PCR and the parasite was not detected from any other fish held at that site during either the September or the May exposure. From these results, we conclude that C. shasta is not likely to have contributed significantly to the decline of steelhead populations throughout Puget Sound.     

Comparative susceptibility of Deschutes River, Oregon, Tubifex tubifex populations to Myxobolus cerebralis

Dams along the Deschutes River (DR) in central Oregon have blocked fish migration for over 40 years. Reestablishment of anadromous fish runs above the dams as part of a fish passage plan may introduce fish pathogens, such as Myxobolus cerebralis, the myxozoan parasite that causes salmonid whirling disease. This parasite is carried by adult salmon that stray into the DR system during their return to enzootic areas of the upper Columbia River basin, and it is now known to be established in at least one lower DR tributary. The life cycle of M. cerebralis involves two obligate hosts: a salmonid and the oligochaete worm Tubifex tubifex. To determine the likelihood of parasite establishment above the DR dams, we conducted benthic sediment surveys between 1999 and 2007 and found that T. tubifex had a patchy distribution and low relative abundance. Mitochondrial 16S ribosomal DNA gene analysis indicated that two lineages of T. tubifex (III and VI) were present both above and below the dams. Laboratory susceptibility studies to characterize differences in infection prevalence and parasite production between nine T. tubifex populations revealed that production varied considerably among exposed groups and was proportional to the number of lineage III worms present. Our results suggest that M. cerebralis could become established above the dams if infected fish are allowed passage into the upper DR system, but not all areas of the DR basin can be classified as having the same likelihood for parasite establishment, and the potential impact will be location dependent.     

Comparative Susceptibility of Deschutes River,Oregon, Tubifex tubifex Populations to Myxobolus cerebralis

Abstract

Dams along the Deschutes River (DR) in central Oregon have blocked fish migration for over 40 years. Reestablishment of anadromous fish runs above the dams as part of a fish passage plan may introduce fish pathogens, such as Myxobolus cerebralis, the myxozoan parasite that causes salmonid whirling disease. This parasite is carried by adult salmon that stray into the DR system during their return to enzootic areas of the upper Columbia River basin, and it is now known to be established in at least one lower DR tributary. The life cycle of M. cerebralis involves two obligate hosts: a salmonid and the oligochaete worm Tubifex tubifex. To determine the likelihood of parasite establishment above the DR dams, we conducted benthic sediment surveys between 1999 and 2007 and found that T. tubifex had a patchy distribution and low relative abundance. Mitochondrial 16S ribosomal DNA gene analysis indicated that two lineages of T. tubifex (III and VI) were present both above and below the dams. Laboratory susceptibility studies to characterize differences in infection prevalence and parasite production between nine T. tubifex populations revealed that production varied considerably among exposed groups and was proportional to the number of lineage III worms present. Our results suggest that M. cerebralis could become established above the dams if infected fish are allowed passage into the upper DR system, but not all areas of the DR basin can be classified as having the same likelihood for parasite establishment, and the potential impact will be location dependent.

Received July 2, 2010; accepted October 24, 2010     

Detection of Myxobolus (Myxosoma) cerebralis in Salmonid Fishes in Oregon

Abstract

Myxobolus (Myxosoma) cerebralis, the etiological agent of whirling disease, was detected in salmonid fish populations in northeastern Oregon. This is the first record of M. cerebralis in the Pacific Northwest of the USA. During an epizootiological survey for the parasite, two methods for spore detection were compared, and an efficient procedure for determining M. cerebralis infection in adult fish was developed. The enzyme digest method was more efficient than the plankton centrifuge procedure for examination of numerous individual lots of fish processed during the survey. Sampling only the area around the otoliths was at least as effective as sampling entire heads for detection of spores in infected fish.     

Demonstration of the Specificity of the Salmonid Hurnoral Response to Renibacterium salmoninarum with a Monoclonal Antibody against Salmonid Immunoglobulin

Abstract

The specificity of the antibody response of salmonids to Renibacterium salmoninarum antigens was demonstrated by western blotting techniques that utilized a monoclonal antibody against salmonid immunoglobulin. In this study, the specificity of the response in immunized chinook salmon Oncorhynchus tshawytscha was compared with the response in naturally infected chinook salmon and coho salmon O. kisutch, and immunized rabbits. The antibody response in immunized salmon and rabbits and the naturally infected fish was primarily against the 57–58kilodalton protein complex. In addition to recognizing these proteins in the extracellular fraction and whole-cell preparations, antibody from the immunized salmon and rabbits detected four proteins with lower molecular masses. Western blotting techniques allow identification of the specific antigens recognized and are a useful tool for comparing the immunogenicity of different R. salmoninarum preparations. Immunofluorescent techniques with whole bacteria were less sensitive than western blotting in detecting salmonid anti-R. salmoninarum antibody.     

Survey of Salmonid Pathogens in Ocean-Caught Fishes in British Columbia,Canada

Abstract

A survey of wild fishes captured around marine net-pen salmon farms and from open waters for certain salmonid pathogens was conducted in the coastal waters of British Columbia. Viral hemorrhagic septicemia virus was detected in Pacific herring Clupea pallasi, shiner perch Cymatogaster aggregata, and threespine sticklebacks Gasterosteus aculeatus. Infectious hematopoietic necrosis (IHN) virus was detected in one Pacific herring (collected well away from the farms) and in tube-snouts Aulorhynchus flavidus and shiner perch collected from a farm experiencing an IHN outbreak. Renibacterium salmoninarum was observed in moribund Pacific hakes Merluccius productus collected from within a net-pen and was also detected in several ocean-caught salmon. Aeromonas salmonicida subsp. salmonicida (typical strain) was isolated from a juvenile chinook salmon Oncorhynchus tshawytscha, whereas the atypical strain of this organism was isolated from a lingcod Ophiodon elongatus. Loma salmonae (Microsporea) was observed in chinook salmon, chum salmon Oncorhynchus keta, coho salmon O. kisutch, sockeye salmon O. nerka, and pink salmon O. gorbuscha, all of which were captured well away from net-pens. Loma spp. (Microsporea) were observed in the gills of shiner perch, lingcod, Pacific tomcod Microgadus proximus, Pacific cod Gadus macrocephalus, walleye pollock Theragra chalcogramma, and sablefish Anoplopoma fimbria; all but the first species represent new hosts for Loma. Epitheliocystis, caused by a chlamydia-like organism, was detected in the gills of chinook salmon, chum salmon, coho salmon, pink salmon, lingcod, Pacific cod, Pacific hakes, Pacific tomcod, walleye pollock, sablefish, shiner perch, Dover soles Microstomus pacificus, Pacific sanddabs Citharichthys sordidus, and various species of rockfish Sebastes spp., most of which represent new host records for this infection.     

A Digenean Metacercaria (Apophallus sp.) and a Myxozoan (Myxobolus sp.) Associated with Vertebral Deformities in Cyprinid Fishes from the Willamette River,Oregon

Abstract

A high prevalence of vertebral deformities has been observed in various fishes, especially cyprinids, from certain regions of the Willamette River for many years. One proposed source of these deformities is exposure to toxicants. Histological evaluation of affected chiselmouth Acrocheilus alutaceus revealed that all lesions associated with vertebrae were associated with metacercariae of digenean trematodes. Approximately half of the northern pikeminnow Ptychocheilus oregonensis had infections in which metacercariae were associated with these lesions. Metacercariae were also associated with vertebral lesions in three of four affected peamouth Mylocheilus caurinus. Many metacercariae that were present within the vertebral bodies were associated with bony dysplasia and bony proliferation in all three species. We also evaluated the association of the metacercariae with the vertebral deformities, using intact fish that had been cleared with trypsin. Fish from the affected regions had a much higher prevalence of metacercariae and deformities and a greater abundance of metacercariae than those in the reference site. Chiselmouths had more deformities and metacercariae than northern pikeminnow. In all fish species, 77% of deformities were directly associated with metacercariae; in chiselmouths, about 95% of the deformities exhibited this relationship. Two types of metacercariae were identified in affected fish: Apophallus sp. (Heterophyidae) and a neascus type (Strigeidida). The Apophallus sp. appeared to be more closely associated with the skeleton deformities. A Myxobolus sp. morphologically similar to M. cyprini was also associated with the vertebral lesions in about 50% of the northern pikeminnow and 5% of the chiselmouths. Intact plasmodia were found in somatic muscle, and lesions containing free spores were often located at bone surfaces. This survey demonstrates that metacercariae (probably Apophallus sp.) and a Myxobolus sp. are major causes of the vertebral deformities seen in cyprinid fishes from certain regions of the Willamette River.     

间接法评定绵羊瘤胃丙酸产生、吸收和流通规律研究

利用非同位素标记丙酸的启动－连续灌注的方法，采用非标记酸灌注条件下计算丙酸基本产生量的原理，研究了绵羊瘤胃碳水化合物产生丙酸的基本速率和通过灌注提高丙酸产生速率后，丙酸在瘤胃的消失率，离开瘤胃的流通速率；丙酸在瓣胃和真胃及小肠的吸收及其它有关液相指标的影响。研究表明：当试验绵羊饲喂粗精比为54：46的日粮并满足维持饲养水平时，测得的丙酸基本产生速率为22．4mmol/h，瘤胃丙酸库容量为51.94mmol,仅占丙酸日产量的9．6％，还确定了瘤胃灌注丙酸后获得稳态的条件是：瘤胃液相pH的变异系数CV＜0．5％，丙酸浓度的变异系数＜6％，标记物Co浓度的变异系数＜5％；丙酸在瘤胃的吸收速率与其在瘤胃的产生速率成正比（P＜0．01），当丙酸的产生速率从37．14提高至145.07mmol/h时，瘤胃吸收的丙酸占丙酸产生量的2／3以上，而随液体离开瘤胃的丙酸不足丙酸产生量的1／3。进一步的研究证实，离开瘤胃的丙酸在瓣胃和真胃有96％以上被吸收，有3％－4％进入十二指肠；同时还获得了一系列通过瘤胃丙酸产生速率（PROD丙酸，mmol/h）预测其它液相特性指标的关系方程。     

Occurrence of Aeromonas salmonicida,Renibacterium salmoninarum,and Infectious Pancreatic Necrosis Virus in Ontario Salmonid Populations

Abstract

The results of samples collected from private and government fish farms and wild and feral fish populations in Ontario from 1981 to 1995 were synthesized to obtain prevalence estimates in salmonids at both the fish and site levels for three pathogens. Renibacterium salmoninarum and Aeromonas salmonicida were both detected on at least one site for every year investigated. Ontario Ministry of Natural Resources (OMNR) culture stations had the highest percentages of sites with infected fish for R. salmoninarum. Natural water bodies had the highest percentages of sites with infected fish for A. salmonicida. Infectious pancreatic necrosis virus (IPNV) was only detected sporadically on some commercial farms and never in OMNR hatcheries or in wild or feral fish. Although screening for any virus that would yield cytopathological effect was carried out during all the years surveyed, no virus other than IPNV was isolated. The low prevalence and “source-specific” presence of IPNV in Ontario demonstrates the necessity of representative sampling for the detection of rare pathogens. It was estimated that, overall, less than 1% of all fish in the sampled populations were infected with each of the three pathogens for almost every year studied. The importance of summarizing pathogen-testing data and the possible implications on disease control policy planning and assessment are discussed.     

Observations on the Plerocercoid Stage of the Tapeworm Ligula in Three Species of Fish from the Lower Crooked River of Central Oregon

Abstract

Tapeworms in the genus Ligula are cosmopolitan parasites whose plerocercoid stages are found worldwide in fishes of the families Cyprinidae and Catostomidae. Examination of chiselmouth Acrocheilus alutaceus, northern pikeminnow Ptychocheilus oregonensis, and bridgelip sucker Catostomus columbianus revealed the presence of Ligula in the lower Crooked River system of central Oregon. This represents the first report of Ligula intestinalis in two of these host species: chiselmouth and bridgelip sucker. Although most hosts appeared healthy, large external lesions were noted on some bridgelip suckers in close association with a Ligula plerocercoid. The largest plerocercoid recovered was 101.5 cm relaxed length and may represent the longest plerocercoid of Ligula reported from North America.     

遗传同型交配下母子间基因型联合分布的信息熵性质

定义了遗传同型交配下一对等位基因群体的基因库信息熵和基因型信息熵，给出并讨论了世代交替中母子间基因型联合分布及其信息熵性质。并从信息角度加以解释；最后，应用Matlab软件进行数据模拟，验证了所得结论的正确性。     

Flavobacterium psychrophilum Infections in Salmonid Broodstock and Hatchery-Propagated Stocks of the Great Lakes Basin

Bacterial coldwater disease (BCWD), caused by Flavobacterium psychrophilum, threatens wild and propagated salmonids worldwide and leads to substantial economic losses. In addition to being horizontally transmitted, F. psychrophilum can be passed from infected parents to their progeny, furthering the negative impacts of this pathogen. In Michigan, both feral and captive salmonid broodstocks are the gamete sources used in fishery propagation efforts. A 5-year study was initiated to follow the prevalence of systemic F. psychrophilum infections in feral broodstocks of four species (steelhead Oncorhynchus mykiss [potadromous Rainbow Trout]; Coho Salmon O. kisutch; Chinook Salmon O. tshawytscha; and Atlantic Salmon Salmo salar) residing in three Great Lakes watersheds. Additionally, captive broodstocks of four species (Rainbow Trout, Brown Trout Salmo trutta, Lake Trout Salvelinus namaycush, and Brook Trout Salvelinus fontinalis) maintained at two facilities were assessed for the presence of F. psychrophilum. The resultant offspring from each broodstock population were sampled for F. psychrophilum infections multiple times throughout hatchery residency. Using selective flavobacterial culture and PCR confirmation, F. psychrophilum was detected in all broodstocks except the captive Lake Trout and Brook Trout. Logistic regression analysis demonstrated that among the infected feral broodstocks, Chinook Salmon from the Lake Michigan watershed had the highest prevalence of systemic F. psychrophilum infection (mean = 63.2%). Among the captive broodstocks, the Gilchrist Creek strain of Brown Trout had the highest infection prevalence (mean = 5%). Collectively, the captive broodstocks were found to have significantly lower infection prevalence than the feral broodstocks. Despite the high prevalence of systemic F. psychrophilum infections in many broodstock populations, the bacterium was rarely detected in their progeny during hatchery rearing. However, heavy losses associated with clinical BCWD outbreaks did occur. Collectively, our results reinforce that BCWD continues to threaten Great Lakes basin salmonids.

Received April 6, 2015; accepted August 25, 2015     

Morphologic Peculiarities of the Renal Cortical Vasculature Connected with Blood Redistribution in the Kidney of the Domestic Pig

The cortical blood vessels from 2 to 8 month old Camborow hybrid pigs and Belgium landrace pigs were studied using histologic and semithin sections as well as corrosion casts and cleared preparations of intravascular injection. It was established that the cortical blood vessels of the porcine kidney possess peculiarities that may regulate the redistribution of blood in the cortex. These peculiarities were found in the interlobular arteries, in the efferent arterioles of midcortical nephrons, in afferent arterioles of juxtamedullar glomeruli, and in the glomerular capillary networks. It was established that the number of renal corpuscles is different in the various zones of the cortex.