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1.
Abstract

A survey of 3–8-year-old peamouths Mylocheilus caurinus collected from the lower Fraser River, British Columbia, revealed 100%, infection by a myxosporean identified as Myxobolus cyprini based on spore morphology, site of infection, and associated pathological changes. Myxobolus cyprini is a common myxosporean parasite of several species of cyprinid fishes (family Cyprinidae) in Europe, the former USSR, and China, but this is the first report of this myxosporean in the Western Hemisphere. The source of the infection in peamouths—whether the parasite is endemic to North America or has been imported with exotic cyprinids from Europe or Asia—is unknown. It is also possible that the myxosporean from peamouths is very closely related to, but a distinct species from, M. cyprini of Eurasia. As reported from European cyprinid fishes, the myxosporean in peamouths developed in the skeletal muscle, and disseminated spores were found associated with chronic inflammation in the visceral organs.  相似文献   

2.
Abstract

Three myxosporeans were encountered in the cranial tissues of a California population of rainbow trout Oncorhynchus mykiss examined for the presence of Myxobolus cerebralis, the causative agent of whirling disease. Typical spores of M. cerebralis and a previously undescribed species of Myxobolus were found in the cranial tissues prepared by the pepsin HCl-trypsin digestion method. Henneguya zschokkei was also detected in digest preparations of cranial tissues, but was more numerous when branchial cartilage was included in the preparations. Microscopic examinations of tissues of individual rainbow trout showed occasional infections with both myxobolid species. Myxobolus cerebralis trophozoites and spores were found in the cranial and gill cartilage, and Myxobolus sp. was found in the brain and spinal cord. Henneguya zschokkei was also found within granulomas in the connective tissues below the gill arch. Both M. cerebralis and H. zschokkei were associated with a chronic inflammatory response in their respective tissues. In contrast, the Myxobolus sp. spores were found in pockets within the nervous tissues with no detectable host response. The spore measurements, calculated from fresh digests of infected tissues for the three myxosporeans (N = 20), for length × width × thickness in micrometers (SD) were 11.7 (0.6) without tails and 42.6 (5.2) with tails × 7.7 (0.8) × 7.0 (0.1) for H. zschokkei, 9.9 (0.4) × 8.4 (0.1) × 6.5 (0.3) for M. cerebralis, and 12.7 (0.7) × 10.5 (1.0) × 9.5 (0.8) for Myxobolus sp. Examined under scanning electron microscopy, the latter two species were morphologically similar although distinctive in size.  相似文献   

3.
Abstract

Effects of temperature and aging on viability and infectivity of laboratory-produced actinosporean triactinomyxon spores (infective stage of the organism causing whirling disease) were studied. In vitro staining of triactinomyxon spores with vital fluorescein diacetate correlated with the ability of the spores to infect fry of rainbow trout Oncorhynchus mykiss. The experimentally produced actinosporean stage of Myxobolus cerebralis was short-lived, persisting for only 3–4 d at 12.5°C and for less time at warmer temperatures. The vital staining method has potential for screening therapeutants intended to control myxosporean infection of fish.  相似文献   

4.
Abstract

The intensity and prevalence of whirling disease was tested by exposure of 2-monthold fry and 1-, 2-, and 3.5-year-old adults of rainbow trout Oncorhynchus mykiss to a known number of laboratory-produced Myxobolus cerebralis at the actinosporean triactinomyxon stage. Fry exposed to graded concentrations of infectivity (triactinomyxons) for 3 h were individually examined for spores of Myxobolus cerebralis 5 and 6 months later. Exposure of fish to the lowest doses, 1 and 10 triactinomyxons per fish, did not result in detectable myxosporean spores. Fish that became lightly infected by a dose of 100 triactinomyxons per fish experienced a decrease in the incidence of infection between 5 and 6 months after exposure. A linear relationship was found between the numbers of recovered myxosporean spores and doses of 100–10,000 triactinomyxons per fish, and the spore burden appeared to plateau at doses of 10,000–100,000 triactinomyxons per fish. Adult fish continuously exposed to the highest dose of triactinomyxons for 3.5 months were infected and asymptomatic, however, the severity of myxosporean infection decreased with increased age of fish. This information may help in controlling whirling disease in salmonids.  相似文献   

5.
Abstract

Laboratory exposures to the infectious stages (triactinomyxons) of Myxobolus cerebralis demonstrated a range of susceptibility to whirling disease among four species of inland salmonids. Replicate groups of each species were exposed to two concentrations of triactinomyxons, a low dose (100–200 per fish) and a high dose (1,000–2,000 per fish). Exposed fish were evaluated for clinical signs, for severity of microscopic lesions at 35 d, 2 and 5 months, and for spore concentrations in the head cartilage at 5 months. A standard strain of rainbow trout Oncorhynchus mykiss matched for age served as a susceptible species control. Rainbow trout, westslope cutthroat trout O. clarki lewisi, Yellowstone cutthroat trout O. clarki bouvieri, and bull trout Salvelinus confluentus were susceptible to M. cerebralis infections. Clinical signs, including radical swimming (“whirling”) and black tails, were observed at 7 weeks postexposure among rainbow and cutthroat trout challenged at 3 weeks of age. Clinical signs were rare among bull trout exposed at an age of 4 weeks and absent among rainbow and cutthroat trout exposed at 3 months posthatch. Most rainbow, cutthroat, and bull trout were found to be infected when examined at 5 months postexposure. The most severe microscopic lesions among infected fish at 5 months postexposure were found among rainbow trout. Cutthroat trout had less severe lesions, bull trout had mild infections, and no evidence of infection was found among Arctic grayling Thymallus arcticus. Mean spore concentrations among infected fish correlated with the severity of microscopic lesion scores. Rainbow trout had mean concentrations of spores in head cartilage reaching 106, whereas more resistant species such as bull trout had 104 spores; no spores were found among Arctic grayling at 5 months postexposure.  相似文献   

6.
Abstract

Spores identified as Myxobolus neurobius were found in head homogenates of both wild young Atlantic salmon Salmo salar and Arctic char Salvelinus alpinus. Formalin-preserved spores from Atlantic salmon measured an average of 12.9 × 9.4 μm and contained two polar capsules that measured 6.4 × 2.9 μm. The spores from the Arctic char appeared morphologically identical by bright-field microscopy to those from the Atlantic salmon except they measured 13.7 × 9.6 μm and had polar capsules that measured 6.9 × 3.4 μm. Myxobolus neurobius has not previously been reported from Atlantic salmon or Arctic char.  相似文献   

7.
Abstract

A whirling-disease-resistant strain of rainbow trout Oncorhynchus mykiss (GRHL strain) derived from a backcross of an F1 hybrid of two strains (German strain × Harrison Lake strain) with German strain females, was compared with the Ten Sleep (TS) strain of rainbow trout. The GRHL strain had consistently superior growth and feed conversion in two consecutive hatchery trials. Hatching and mortality rates were similar between strains. Both strains were stocked into two Utah reservoirs (Hyrum, Porcupine), and a third, Causey Reservoir, was monitored as a control for seasonal variation in prevalence of Myxobolus cerebralis. A total of 1,323 salmonids captured by gill net in spring and fall sampling between 2006 and 2008 were tested for M. cerebralis via pepsin-trypsin digest methods. Only eight of these (<1% per species) had clinical signs consistent with whirling disease. In both reservoirs, GRHL survived better than the TS and had higher growth rates. The prevalence of M. cerebralis was significantly lower for GRHL (18.1%) than TS (50.0%) in Porcupine Reservoir. In Hyrum Reservoir the trend was similar, but prevalence was lower and did not significantly differ between GRHL (9.6%) and TS (23.1%). For infected fish, no significant differences were observed between strains in myxospore counts in either Hyrum (GRHL = 911–28,244 spores/fish [spf], TS = 1,822–155,800 spf) or Porcupine (GRHL = 333–426,667spf, TS = 333–230,511 spf) reservoirs. Unmarked rainbow trout in both reservoirs had significantly higher myxospore counts than stocked fish of either strain. There were significant differences in M. cerebralis prevalence and myxospore loads among other naturally reproducing salmonids in the reservoirs. The trend in susceptibility was cutthroat trout Oncorhynchus clarkii > kokanee Oncorhynchus nerka > brown trout Salmo trutta. The GRHL performed well in both hatchery and field settings and is recommended for stocking programs.

Received December 28, 2011; accepted February 2, 2012  相似文献   

8.
Abstract

A nonradioactive in situ hybridization (ISH) protocol was developed to detect Myxobolus cerebralis, the causative organism of whirling disease, in its primary host, rainbow trout Oncorhynchus mykiss, and in its alternate oligochaete host, Tubifex tubifex. A cocktail of three oligonucleotide primers (derived from the small subunit ribosomal DNA sequence) directed at target sequences of the parasite DNA was tailed at the 3′ end with digoxigenin-labeled deoxyuridine triphosphate (DIG-dUTP). Labeled probes were hybridized to parasite DNA present in deparaffinized tissue sections from infected trout and oligochaetes. The bound probes were visualized after modifications of existing ISH protocols. By using the new ISH procedure, the parasite was found in target tissues of subclinically and clinically infected fish and tubificid oligochaetes after exposures of these hosts to triactinomyxons and mature spores, respectively. The probe did not bind with salmonid tissues infected with two other myxosporean parasites, Ceratomyxa shasta or the PKX organism, or to a Myxobolus sp. infecting the cartilage of plain sculpin Myoxocephalus jaok. These initial results indicate that ISH is an effective and specific test for detecting Myxobolus cerebralis in its fish and oligochaete hosts.  相似文献   

9.
During a survey on the Myxobolus infection of two cyprinid fishes, the ide (Leuciscus idus) and the roach (Rutilus rutilus), myxosporean developmental stages were found around the arteries of the gill filaments and in the gill lamellae. An analysis of the 18S rDNA sequences of these stages revealed that plasmodia developing in the ide belonged to Myxobolus elegans, those developing in the gill lamellae of the roach corresponded to M. intimus, while plasmodia developing in close contact with the cartilaginous gill rays proved to be developmental stages of M. feisti. A strict seasonal cycle with a very long intrapiscine development was recorded for M. elegans and M. intimus. Developing plasmodia of the latter Myxobolus spp. occurred from early summer to next spring, and spore formation took place only in April. No seasonality associated with M. feisti infections was found. Developing plasmodia and mature spores of this species occurred simultaneously in different seasons of the year. Myxobolus feisti spore formation always occurred in close contact with the cartilaginous tissue of the gill filaments but spores were rarely encapsulated in the cartilaginous gill rays.  相似文献   

10.
Abstract

In 1991, the poor physical condition of largemouth bass Micropterus salmoides from Lake Harris, Florida, was associated with the decline of the lake's fishery. The swim bladders of emaciated bass had mild inflammation and ecchymotic hemorrhages. A mycoplasma-like organism isolated from swim bladders was initially believed to be the causative agent. The organism was later identified as Acholeplasma laidlawii by using a fluorescent antibody procedure and was demonstrated to be nonpathogenic. Parenteral injection of the organism into healthy largemouth bass fingerlings produced no signs of disease or difference in growth rate compared with control fish during a 16-month period. Field studies resulted in isolation of A. laidlawii from black crappies Pomoxis nigromaculatus, bluegills Lepomis macrochirus, and redear sunfish L. microlophus, but not from noncentrarchids in Lake Harris or from any fish species in a control fishery (Lake Holly, Florida). The absence of organisms in all emaciated bass, our inability to reproduce the disease, and isolation of the organism from seemingly healthy fish suggest this organism was not pathogenic.  相似文献   

11.
Abstract

Two sizes of fingerling Snake River cutthroat trout Oncorhynchus clarkii behnkei and Colorado River rainbow trout O. mykiss were raised at hatcheries testing negative for Myxobolus cerebralis and stocked into the Dolores and Cache la Poudre rivers from 1999 to 2001. Populations were resampled over a 2-year period to determine which species and size combination had the highest growth and survival rates. Fish were tested for M. cerebralis via polymerase chain reaction and pepsin?trypsin digest analyses. Growth and survival rates between the species and size groups were not significantly different in either river. In the Dolores River, annual survival for both species and sizes of fish combined ranged from 0.063 to 0.12. In the Cache la Poudre River, survival for both sizes of rainbow trout was 0.004; survival for cutthroat trout ranged from 0.182 to 0.53. Larger fish had higher growth rates than smaller fish, and cutthroat trout had higher rates than similar sizes of rainbow trout. In both rivers, a higher percentage of the rainbow trout sample was infected than in the cutthroat trout sample. Rainbow trout also had a higher mean number of spores per head than cutthroat trout, and small rainbow trout had higher spore counts than large rainbow trout. Survival rates for cutthroat trout in the Cache la Poudre River were the highest of any of the groups, suggesting a difference that is biologically significant. Raising fingerlings to sizes greater than 100 mm can improve poststocking survival. If rainbow trout are stocked into contaminated waters, raising fingerlings to a larger size does not appear to improve growth or survival rates. Stocking rainbow trout in the spring could maximize growth rates but will expose fish to greater triactinomyxon densities, resulting in higher intensities of infection.  相似文献   

12.
Abstract

The Alaska Department of Fish and Game fish pathology laboratory received a rainbow trout Oncorhynchus mykiss from the Alaska Peninsula that was suspected of having whirling disease based on the display of aberrant swimming behavior and a deformed spine. We tested for Myxobolus cerebralis using standard pepsin–trypsin digest and molecular procedures, which yielded negative results. However, many oval shaped myxospores were observed in brain smears and were confirmed to be those of the morphologically similar M. neurotropus based on a diagnostic assay using PCR. The known geographic distribution of this parasite includes Idaho, Washington, Utah, Oregon, California, and now, Alaska. Whether this species is an emerging parasite is not known because it was only described a few years ago. Given the severe infection found in this rainbow trout, perhaps the considerable displacement of neurological tissues and subsequent pressure on peripheral nerves could have contributed to the spinal curvature and accompanied abnormal swimming. Conversely, the M. neurotropus infection may have been incidental and the spinal deformity may have actually been due to one of several nonspecific developmental or congenital causes. Further studies on geographic distribution and impact on host fitness will probably determine the importance of this species to fish health.

Received March 1, 2012; accepted June 15, 2012  相似文献   

13.
Abstract

Proliferative gill disease (PGD), a condition not previously reported in wild fish, was found in two channel catfish Ictalurus punctatus sampled from the Tennessee-Tombigbee Waterway in Mississippi during June and July 1989. The parasite thought to cause PGD was observed in only one of the fish, but the distinctive lesions associated with this disease were prominent in both of the channel catfish. Organisms resembling the PGD parasite were also found in the gills of 4 of 18 largemouth bass Micropterus salmoides and 6 of 20 bluegills Lepomis macrochirus, but there was little or no host response to these parasites.  相似文献   

14.
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15.
Abstract

Several species of marine fish caught in the wild and of freshwater ornamental fish were used in this study. Infected organs (liver, spleen, and kidney) were sampled for mycobacteria. Decontaminated tissue samples were plated onto selective media for mycobacterial recovery. After initial isolation, fluorescent and acid-fast staining techniques identified bacterial colonies to genus. Profiles of biochemical growth characteristics were used to further identify the isolates to species. Five species of Mycobacterium were identified: M. simiae, M. scrofulaceum, M. marinum, M. chelonae, and M. fortuitum. Of these, M. simiae and M. scrofulaceum have not been previously reported from fish. Tissue samples containing focal granulomatous lesions were prepared for electron microscopic examination.  相似文献   

16.
In a three-year survey of myxosporean infections of the bleak (Alburnus alburnus), involving the examination of 205 fish specimens from the River Danube and 50 from Lake Balaton, four Myxobolus species (two gill parasites, one fin parasite and a species parasitising the skeletal muscles) were detected. Two of the species could be identified as M. alburni and M. obesus. Of the other two species, the gill parasite proved to be a hitherto undescribed species which is described here as a new species by the name of M. margitae. One of the two gill-parasitic species, M. obesus, formed plasmodia in the respiratory lamellae of the gill filaments, while the plasmodia of M. margitae n. sp. were formed in the afferent artery of the primary gill filaments. The plasmodia containing spores morphologically identifiable with the species M. alburni were located in the connective tissue between the fin rays. The less frequently found muscle-parasitic Myxobolus species has not been identified precisely. The plasmodia of M. obesus were found in the fish in May and June, while those of M. alburni and M. margitae n. sp. in July and August. The prevalence of infection in fish examined in these periods was 15.5% for M. obesus, 11.5% for M. margitae and 14.0% for M. alburni.  相似文献   

17.
Abstract

We chose a hypolimnetic-release tailwater of the San Juan River, New Mexico, to characterize the etiology of whirling disease, a parasitic infection of salmonids. We sampled a 2-km reach of the tailwater in August and December 2001 and June 2002 to characterize environmental factors influencing the distribution and density of Tubifex tubifex lineages and Myxobolus cerebralis infection rates. Shortly after the scouring flow, organic matter in sediments and T. tubifex densities increased within deep habitats. In contrast, no differences were observed in T. tubifex densities and organic matter collected from shallow habitats throughout the three sampling dates. Within this study area, we found three sympatric lineages of T. tubifex (lineages I, III, and VI). Lineage VI dominated riffle reaches, whereas lineages I, III, and VI were observed in pool habitats. Myxobolus cerebralis infection rates were higher in T. tubifex collected in pool habitats (3.01%) than in those collected in riffle habitats (0.51%). Only lineage III exhibited infection with M. cerebralis. We suggest that the habitat and genotype of T. tubifex are important in characterizing prevalence of disease within the San Juan River tailwater. Scouring flow may have a beneficial effect on disease severity in salmonid hosts by reducing organic loading and hence T. tubifex abundance in deep habitats.  相似文献   

18.
Abstract

Wild striped bass Morone saxatilis in Chesapeake Bay are experiencing a high prevalence of mycobacteriosis, which produces granulomatous lesions of the skin and visceral organs. Culture-based studies have indicated that the newly described species Mycobacterium shottsii and M. pseudoshottsii are the dominant isolates from diseased fish. The classical fish pathogen M. marinum is also found, albeit at much lower frequencies. Both M. shottsii and M. pseudoshottsii are extremely slow-growing on standard selective media, and up to 12 months may be required for isolation and characterization. Epidemiological studies of mycobacteriosis in Chesapeake Bay would therefore benefit from rapid molecular assays with which to detect these species in fish. In this paper, we describe the development of polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) assays capable of detecting M. shottsii, M. pseudoshottsii, and, in most instances, coinfections thereof in striped bass tissues. In addition, PCR–RFLP assays were designed to detect M. marinum and other as-yet-undescribed Mycobacterium spp. present in Chesapeake Bay striped bass. Comparison of these molecular assays with culture-based techniques using splenic tissue from wild striped bass yielded generally concordant results and demonstrated the applicability of these techniques to the study of wild fish.  相似文献   

19.
Abstract

Susceptibility to infection by the myxosporean parasite Myxobolus cerebralis was compared among strains of cutthroat trout Oncorhynchus clarki in two separate exposure tests in the laboratory. In both tests, each strain was exposed to 1,000 triactinomyxons/fish for 2 h in 8.0 L of water. In the first test, three strains of 10-week-old cutthroat trout were compared: two strains of Bonneville cutthroat trout O. c. utah (Bear Lake and southern Bonneville strains) and Yellowstone cutthroat trout O. c. bouvieri. In the second test, these strains plus Snake River fine-spotted cutthroat trout O. c. subsp. and Colorado River cutthroat trout O. c. pleuriticus were exposed at either 5 or 10 weeks of age. The prevalence of the M. cerebralis infection was determined by single-round polymerase chain reaction (PCR) assay 5 weeks after exposure. In the first test, the prevalence was significantly lower in the Bear Lake strain of Bonneville cutthroat trout (78.5%) than in the Yellowstone (97.8%) or southern Bonneville (100%) strains when exposed at 10 weeks of age. In the second test, the Bear Lake strain also had significantly lower infection rates after exposure at 5 (54%) or 10 weeks (82%) of age than the other four strains, which did not differ from each other (94–100%). The severity of the infection was also significantly reduced in Bear Lake Bonneville cutthroat trout, as suggested by the strength of the product of the single-round PCR assay. These results suggest that intraspecific differences in susceptibility to M. cerebralis infection exist, further supporting the need to maintain the genetic diversity among subspecies and geographic variants of cutthroat trout.  相似文献   

20.
Abstract

Over an approximately 2-year period, 20,974 fish (trout and other salmonid species) from 230 separate waters (creeks, rivers, lakes, reservoirs, ponds, hatcheries, and irrigation ditches) within 21 of the 22 major drainages in Montana were examined for Myxobolus cerebralis. Nine of the major river drainages have waters containing infected fish: Beaverhead, Big Hole, Blackfoot, Clark Fork above the Bitterroot River, Flathead below the south fork of the Flathead River, Jefferson, Madison, Missouri above the Marias River, and Yellowstone above the Bighorn River. The Beaverhead, Clark Fork above the Bitterroot River, Jefferson, Madison, and Missouri above the Marias River have the greatest number of waters containing fish infected with M. cerebralis. Comparisons of infection levels (number of pooled samples that contain fish infected with M. cerebralis) between species among these drainages show significantly lower levels of infection in brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss in the Missouri above the Marias River drainage and significantly higher levels of infection of rainbow trout in the Jefferson. Comparisons of differences in infection levels between drainages among species show that, in the Beaverhead, Clark Fork above the Bitterroot River, and Madison, infection levels in brown trout are significantly higher than in rainbow trout. This is partially attributed to losses of juvenile rainbow trout because of M. cerebralis infection, leading to biased samples. Histopathologic studies showed lesions were consistently less severe in brown trout than other species and occurred in a different location (gill arches versus ventral calvarium). In six of the nine affected drainages (Beaverhead, Blackfoot, Clark Fork above the Bitterroot River, Flathead below the South Fork, Jefferson, and Madison), infected fish were found at or near the time that intensive sampling was initiated in the spring of 1995. In the three remaining affected drainages (Missouri above the Marias River, Yellowstone above the Bighorn River, and the Big Hole), infected fish were not identified until at least 15 months after the initiation of widespread testing. This indicates that in the first six drainages listed above, the infection was well established prior to 1995 but spread into the last three drainages in the ensuing months. Methods of transmission and the sources of infection are unknown, although the absence of infected fish in state, private, and federal hatcheries in Montana indicates hatchery fish from these sources are not likely to be responsible.  相似文献   

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