首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 685 毫秒
1.
Abstract. A rickettsia-like organism (RLO) was isolated from infected coho salmon, Oncorhynchus kisutch (Walbaum), in cultures from six fish cell lines, but could not be cultured on 41 artificial media. The organism was confirmed by Koch's postulates as the aetiological agent of a systemic disease causing signifieant mortality among coho in Chile. The organism was a Gram-negative, obligate intracellular pathogen frequently observed within intracyto-plasmic vacuoles or inclusions of host cells, and appears to belong to the order Rickettsiales, family Rickettsiaceae and possibly the tribe Ehrlichiae. The organism, as well as the clinical signs and pathology it produces, is described. The disease, originally observed only in coho raised in seawater net pens, was reproduced experimentally in fish in both freshwater and seawater aquaria. Horizontal transmission without parasite vectors was observed in fish in both aquaria. The organism was shown, for the first time, to cause disease and mortality in Atlantic, Salmo salar L., and Chinook, O. tshawytscha (Walbaum), salmon and rainbow trout, O. mykiss (Walbaum). Because of the systemic nature of the disease, it is proposed that it be called 'salmonid rickettsial septicaemia'.  相似文献   

2.
In the last 9 years, epizootics of an icterus condition has affected coho salmon, Oncorhynchus kisutch (Walbaum), reared in seawater cages in southern regions of Chile. At necropsy, fish from field cases exhibited signs of jaundice accompanied by pale light-brown livers and dark spleens. Histopathological and haematological results indicated that these fish presented haemolytic anaemia. After microbiological examination no bacterial or viral agents could be identified as aetiological agents of this disease. In an infectivity trial, coho salmon, Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), were inoculated intraperitoneally with a filtrate of an organ homogenate (0.45 microm) from a diseased coho salmon and held for 60 days in tanks supplied with fresh water. The disease was only reproduced in coho salmon in which mortalities, beginning at day 23 post-inoculation (p.i.), reached a cumulative value of 24% at day 27 p.i. This condition was transmitted to non-inoculated cohabiting coho salmon suggesting that it is a waterborne disease. Thus, this icteric condition is caused by an infectious form of haemolytic anaemia, probably of viral aetiology, and coho salmon are more susceptible than either Atlantic salmon or rainbow trout.  相似文献   

3.
The variation of virulence of Renibacterium salmoninarum , the causative agent of bacterial kidney disease (BKD) in salmonid fish, was studied by infecting rainbow trout, Oncorhynchus mykiss (Walbaum), with two isolates (strains 325 and 932) from diseased Atlantic salmon, Salmo salar L., and one isolate (strain 4366) from an apparently healthy Atlantic salmon. Coho salmon, Oncorhynchus kisutch (Walbaum), were injected with the strain 932 to estimate difference in fish species resistance. Fish were removed by random sampling for other study purposes, a study design possible with analysis of lifetime distributions incorporating both sampling-, death- and survival-times. At the end of the experiment, the rainbow trout infected with strains 325, 932 and 4366 had a survival probability of 33%, 51% and 72%, respectively. The coho salmon infected with strain 932 had a 26% survival probability. The strain differences were significant according to the log-rank test, and the risk ratio between the strains ranged from 1·8 to 5·4. The strain from the apparently healthy fish was least virulent. The survival of the fish species was different over time. Rainbow trout were more likely to die early in the time course, but high numbers of coho died later, resulting in an overall risk of mortality of 1·4 in favour of rainbow trout. Differences in virulence may reflect changed selective pressure on R. salmoninarum when introduced from feral stocks into the environment of fish farms.  相似文献   

4.
Abstract The survival of small-sized (<50.8 cm) chinook salmon, Oncorhynchus tshawytscha (Walbaum), and coho salmon, Oncorhynchus kitsutch (Walbaum), caught by sport fishing was determined to assess the potential for increasing the size limit for these fish. Fishermen were recently catching smaller salmon than in the 1970s, but salmon growth rates had not changed. To be an effective management option, the survival rate of hooked and returned fish must be high. The overall survival rates were high: 76% for chinook salmon and 70% for coho salmon. There was no significant difference in survival of the coho salmon with size of hook used ( P = 0.31). Any mortality among fish was generally acute; fish hooked deep in the mouth or gills generally bled and died shortly after capture. Fish hooked in the gills had a significantly greater mortality ( P = 0.0002). The overall high survival rate for these species was the result of a small proportion of fish being hooked in the gills or deep in the mouth. Since the survival rate of the salmon was high, the size limit could be increased to allow smaller fish to grow to sizes preferred by sport fishermen.  相似文献   

5.
Abstract. Injected vaccines consisting of formalin-killed cells and extracellular antigens prepared from a virulent and an avirulent strain of Aeromonas salmonicida were tested for their efficacy in protecting juvenile coho salmon. Oncorhychus kisutch (Walbaum). Against experimental furunculosis following active and passive immunization. Sera used in the passive immunization experiments were raised in subadult coho salmon and in rabbits. Results indicated that the avirulent strain was inferior to the virulent strain in its immunogenicity for coho salmon. Thus, even though avirulent cells possessed at least one immunogen–an immunogen that was show in passive immunization experiments to be well recognized by rabbits–the immunogen was only inefficiently protection when vaccinated with avirulent cells. Furher, extracellular antigens of the avirulent strain were not protective for coho salmon even though they elicited the production of anti- A. salmonicida agglutinins. In contrast, the killed cells and extracellular antigens of the virulent strain were both immunogenic in coho salmon. By passively immunizing coho salmon with rabbit sera raised against the virulent and the virulent strain produced at least two immunogens, only one of which was shared in common with the avirulent strain. The extra immunogen possessed by the virulent strain is presumably responsible for its superior immunogenicity in coho salmon; the immunogen had the properties of a protein and is believed to be the A-protein.  相似文献   

6.
Abstract. High levels of mortalities have been experienced in farmed coho salmon, Oncorhynchus kisuteh (Walbaum), in the Gulf of Ancud, southern Chile. Most affected fish had similar skin lesions ranging from small areas of raised scales through white raised plaques to shallow ulcers. The fish were also generally dark, lethargic and anorexic. However, some affected fish appeared grossly normal with no skin lesions. Internal pathology consisted of varying degrees of ascites, peritonitis and general pallor. Spleens were generally enlarged. Kidneys and livers were swollen and grey in colour, often with pale focal lesions. Extensive histopathology was present in affected fish with tissue necrosis, intravascular necrotic thrombi, large basophilic cells and basophilic granules, some free in the tissues, some contained within cells. The basophilic granules, known locally as the 'UA', or unidentified agent, were thought to be the main aetiological agent, and are likely to be a rickettsia-like organism.  相似文献   

7.
Abstract. The histopathology associated with naturally acquired vibriosis in chum salmon, Oncorhynchus keta (Walbaum), fingerlings caused by Vibrio anguillarum was compared with that caused by infection with Vibrio ordalii. Pathogenesis of the two forms was found to be different. Bacteraemia caused by V. anguillarum occurred in the early stages with pronounced histopathological changes in blood, loose connective tissue, kidney, spleen, gills and posterior gastrointestinal tract. Bacterial cells appeared uniformly dispersed throughout the affected tissues but were most abundant in the blood. With V. ordalii, bacteraemia developed only in late stages of the disease and the concentration of bacterial cells per ml of blood was less than in the V. anguillarum infection by a factor of 102–103. Tissues with most pronounced changes were skeletal and cardiac muscle, anterior and posterior gastrointestinal tract and the gills. Vibrio ordalii observed in the tissues was not evenly dispersed but was present within tissue as colonies or aggregates of cells. The differences in pathology observed in naturally infected chum salmon were produced experimentally with each pathogen by waterborne exposure of chum; coho, Oncorhynchus kisutch (Walbaum); and chinook salmon, Oncorhynchus tshawytscha (Walbaum). Severe decreases in circulating leucocytes accompanied bacteraemia caused by either bacterial species.  相似文献   

8.
Abstract. To assess the merits of rearing coho salmon, Oncorhynchus kisutch (Walbaum), smolts semi-naturally, trials were made in which 17 groups of tagged smolts, from 4 brood years, were raised on a partially natural diet in a semi-natural habitat. Their subsequent survival, as determined from catch and escapement, was compared with that of four groups of smolts, from the same brood years, raised by a conventional hatchery method. The returns of the semi-natural fish proved lower than or similar to those of the hatchery fish, which attained a maximum survival to catch and escapement of 26%. The survival of the semi-natural fish showed no relation to their location in their linear rearing facility, nor to size of smolt (within a narrow range). Further trials showed that a month's delay in release of the semi-natural fish did not increase returns, contrary to a current predictive model. The distribution of the catches of both kinds of fish was broadly similar in the troll and sport fisheries. It is concludedthat semi-natural rearing of coho smolts is not superior to that of standard hatchery procedures, although it may be favoured for specific locations that lend themselves to this approach.  相似文献   

9.
This study examined whether rapid recovery from stress-induced impairment in predator evasion, observed in previous studies on coho salmon, Oncorhynchus kisutch (Walbaum), was a general characteristic of different stocks of the same species and different species of Pacific salmon. We monitored stress-induced non-predator mortality, predator evasion and Cortisol concentrations of smolts of coho and spring Chinook, O. tshawytscha (Walbaum), after administration of standardized single and multiple handling stresses. Marked differences in the response to handling stress among stocks of coho and spring chinook smolts were evident, with recovery from impaired predator evasion occurring within 24 h of a 30-s handling stress for coho smolts and 24 h of a 1-min handling stress for spring chinook smolts. Differences in stress-induced non-predator mortality among stocks were also observed. The results point to the importance of screening hatchery salmonid stocks to assess differing capabilities of dealing with stress.  相似文献   

10.
In salmonids, growth hormone (GH) stimulates growth, appetite and the ability to compete for food. This study tested the hypothesis that increased GH levels in GH-transgenic coho salmon Oncorhynchus kisutch (Walbaum) increase competitive ability through higher feeding motivation. The transgenic strain of salmon used contained a gene construct consisting of the sockeye metallothionein-B promoter fused to the type 1 growth gene coding region. The transgenic animals (mean size = 250 g) were F1 individuals. In six consecutive feeding trials, the intake of contested food pellets by size-matched pairs consisting of one control (1 year older non-transgenic coho salmon) and one GH-transgenic coho salmon was compared. Pellets were provided sequentially until neither fish took three consecutive pellets; the identity of the fish taking each pellet was noted. Calculated on the three first pellets offered at each feeding trial, the transgenic coho salmon consumed 2.5 times more contested pellets than the controls, supporting the hypothesis that GH transgenesis increases the ability to compete for food. Overall, the transgenic fish consumed 2.9 times more pellets that the non-transgenic controls, indicating a high feeding motivation of the transgenic fish throughout the feeding trials. It appears that GH transgenesis and GH treatments can induce similar changes in the feeding behaviour of salmonids. Depending on how transgenic and wild individuals differ in other fitness-related characters, escaped GH transgenic fish may compete successfully with native fish in the wild.  相似文献   

11.
Salmonid colonization of new streams in Glacier Bay National Park, Alaska   总被引：4，自引：0，他引：4  
Abstract. Following the rapid recession of a neoglacial ice sheet within the last 250 years, colonization of recently deglaciated streams by salmonid fishes was investigated in Glacier Bay National Park, south-eastern Alaska. The primary factors governing the establishment, species diversity composition and abundance of salmonids in Glacier Bay streams were water temperature, sediment loading and stream discharge. No salmonids were found in the turbid meltwater streams emerging from retreating ice. Coho, Oncorhynchus kisutch (Walbaum), and sockeye, Oncorhynchus nerka (Walbaum). salmon and Dolly Vardcn, Salvelinus malma (Walbaum), charr were the first salmonids to colonize the youngest clearwater stream. Juvenile Dolly Varden were more abundant than juvenile coho salmon in the most recently formed clearwater stream because of the characteristic absence of pool habital. Densities of juvenile coho salmon were six times greater in a stream with a series of lakes compared with a stream of similar age without lakes. Future advancement of salmonid stocks will probably depend upon the rate and extent of the development of riparian vegetation and inputs of large woody debris from the developing forest to provide further instream cover, habitat variation and channel stabilization.  相似文献   

12.
Abstract. Studies were conducted to clarify the relationship between growth rate and disease progression of erythrocytic inclusion body syndrome (EIBS) in artificially infected coho salmon, Oncorhynchus kisutch (Walbaum). In the diseased state, the haematocrit values decreased and the number of erythrocytes with inclusions was higher in faster growing fish. Rapid growth was accompanied by an abundance of immature erythrocytes, which had the greatest incidence of inclusion bodies.  相似文献   

13.
In relation to stock enhancement programmes, wild salmon broodfish have been routinely screened for the presence of Renibacterium salmoninarum antigens (Rs‐Ag) for decades. A sudden increase in the prevalence of Rs‐Ag experienced caused extensive problems to this industry as eggs from positive fish are discarded. The prevalence and level of Rs‐Ag were examined in resident and anadromous salmonids in the River Ellidaár system and the progress of Rs‐Ag in a cohort of salmon followed. Both prevalence and Rs‐Ag levels were high in resident salmonids and emigrating salmon smolts in the river system. When the smolts re‐entered their home river as adults the following summer, they were almost free of Rs‐Ag, but the longer they stayed in the river, the more Rs‐Ag they acquired; the majority being positive at spawning. This study demonstrates a high level of Rs‐Ag in salmonids in the River Ellidaár system which significantly reduces in the salmon during its seawater phase. Accordingly, it seems ideal to sample salmon broodfish as soon as possible after ascending the river and subsequently transfer to Rs‐free environment for storage until stripping, which could result in lower Rs‐prevalence and minimize the problems that stock enhancement programmes have faced due to Rs‐positive wild broodfish.  相似文献   

14.
Experimental evidence suggests that olfactory imprinting by salmon occurs during a sensitive period associated with surges in plasma thyroxine (T4) levels during smolting. Life-history studies, however, suggest that imprinting may occur prior to smolting. A possible resolution of this paradox may lie in the finding that exposure of coho salmon, Oncorhynchus kisutch (Walbaum) smolts to novel water sources induced transient increases in plasma T4 levels. If novel water-induced T4 surges occur prior to smolting and T4 surges are required for olfactory imprinting, juvenile salmon experiencing novel water sources as they move through their watershed may learn olfactory waypoints (e.g. stream confluences). To test this hypothesis, we exposed subyearling coho salmon, Oncorhynchus kisutch (Walbaum), to novel odours or water sources at distinct developmental stages. Subyearlings did not demonstrate dramatic increases in plasma T4 levels during smolting and exposure to novel water sources also had no effect on basal T4 levels. Previous studies have indicated that such coho smolts successfully imprint to similar exposure paradigms and home accurately. These results suggest that surges in plasma T4 levels during smolting may not be necessary for olfactory imprinting and accurate homing.  相似文献   

15.
Abstract This study examined juvenile salmonid use of a freshwater tidal creek system draining a wetland on the floodplain of the lower Fraser River, British Columbia, Canada. Chum, Oncorhynchus keta (Walbaum), chinook, O. tshawytscha (Walbaum), and sockeye, O. nerka (Walbaum), salmon fry were abundant in the tidal creeks in spring. The fry were found in non-natal habitat up to 1.5 km from the main channel of the river. The salmon fry ate dipteran adults, larvae and pupae, cyclopoid and harpacticoid copepods, and Collembola. Mysids Neomysis mercedis Holmes (Walbaum), and amphipods, Crangonyx richmondensis occidentalis (Hubricht and Harrison), were also consumed. The upper reaches of an undisturbed creek were the winter rearing habitat for presmolt coho salmon, O. kisutch (Walbaum), where this species ate dipteran pupae and larvae as well as a freshwater isopod, Asellus communis Say (Walbaum).  相似文献   

16.
Somatolactin (SL) is a novel pituitary hormone recently characterized in several fish species. Structural analyses have shown that SL belongs to the growth hormone/prolactin family, and that it is a highly conserved protein. SL is synthesized by the periodic acid/Schiff-positive cells in the pars intermedia, but has an as yet unidentified function(s). We have recently developed a homologous radioimmunoassay for coho salmon SL and measured plasma levels of SL during two stages of the coho salmon life cycle, smoltification and sexual maturation. During smoltification, plasma levels of SL changed almost in parallel with plasma levels of thyroxine; levels increased as morphological indices of smoltification appeared and decreased as smoltification was completed. Following this period, SL levels remained low until the spring prior to spawning. In a separate study, plasma levels of SL were measured in sexually maturing coho salmon that remained in fresh water throughout their life cycle. During the year of sexual maturation, plasma levels of SL gradually increased from the spring onward, reaching peak levels at the time of spawning in November and December. These data are similar to those previously reported for sexually maturing coho salmon that were maintained in seawater prior to spawning (Rand-Weaver et al. 1992). Therefore, increases in plasma SL levels occurred in sexually maturing fish irrespective of whether they were maintained in fresh water or seawater. Peak levels at spawning were higher than those observed during smoltification. Possible roles for SL in metabolism and reproduction are discussed.  相似文献   

17.
Abstract – Although homing behaviour has been observed in juvenile Atlantic salmon, brown trout and resident cutthroat trout, this behaviour has not been well studied in juvenile Pacific salmon. We examined the site fidelity and homing behaviour of juvenile coho salmon ( Oncorhynchus kisutch ) by marking and relocating them within an off-channel habitat. Over 80% of displaced fish returned to the area from which they were originally collected. The proportion of fish that returned to the original location did not vary significantly among three sampling dates. However, we found that this proportion decreased over time in a brackish lagoon when we statistically analysed the data reported by Day (1966) . Our results suggest that juvenile coho salmon exhibit strong site fidelity and are able to return to their home ranges after displacement. These behaviours are likely to be important for the winter survival of juvenile coho salmon.  相似文献   

18.
Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum (Rs), is a serious threat to salmon in aquaculture as well as to wild populations. We have developed a real-time polymerase chain reaction (PCR) for detection of Rs in kidney samples. The PCR is based on detection of unique parts of the 16S rRNA gene of Rs and DNA equivalent to 1-10 Rs genomes was detected per reaction. No cross-reactivity with other fish pathogenic or related bacteria could be demonstrated. Analysis of individual kidney samples collected from BKD classified populations identified 39.9% of the fish as positive by real-time PCR compared with 28.0% by polyclonal enzyme-linked immunosorbent assay (ELISA). The real-time PCR assay was found to be well suited for complementary use with ELISA for diagnosis of BKD, with the ability to detect clinical as well as covert Rs infections. The infection level determined by the polyclonal ELISA and by real-time PCR was significantly correlated.  相似文献   

19.
Abstract. Unfertilized, water-hardened eggs, obtained from a coho salmon, Oncor-hynchus kisutch (Walbaum), with coelomic fluid containing large enough numbers of the kidney disease bacterium, Renibacterium salmoninarum , to make the fluid cloudy (∼4 × 109 cells/ml), were examined by cultural and histological methods to determine (a) whether an earlier finding of the pathogen in coho eggs could be corroborated, and (b) whether iodine (500 mg/l, in the form of povidone-iodine) was as effective at ridding them of the intra-ovum pathogen as it was at freeing them of the extra-ovum pathogen. The results confirmed that the pathogen does indeed occur within the egg (11–6%-15-l % of the eggs were infected in this manner), and suggested a location in the yolk for the pathogen. The findings also indicated that while iodine was very effective in killing the pathogen on the surface of the eggs it was completely ineffective in reducing the prevalence of the intra-ovum infections. The results point out the need for a method for treating eggs internally and confirm the inadvisability of using eggs from salmonids with cloudy coelomic fluid.  相似文献   

20.
Michigan's fisheries rely primarily upon the hatchery propagation of salmonid fish for release in public waters. One limitation on the success of these efforts is the presence of bacterial pathogens, including Aeromonas salmonicida, the causative agent of furunculosis. This study was undertaken to determine the prevalence of A. salmonicida in Michigan fish, as well as to determine whether biochemical or gene sequence variability exists among Michigan isolates. A total of 2202 wild, feral and hatchery‐propagated fish from Michigan were examined for the presence of A. salmonicida. The examined fish included Chinook salmon, Oncorhynchus tshawytscha (Walbaum), coho salmon, O. kisutcha (Walbaum), steelhead trout, O. mykiss (Walbaum), Atlantic salmon, Salmo salar L., brook trout, Salvelinus fontinalis (Mitchill), and yellow perch, Perca flavescens (Mitchill). Among these, 234 fish yielded a brown pigment‐producing bacterium that was presumptively identified as A. salmonicida. Further phenotypic and phylogenetic analyses identified representative isolates as Aeromonas salmonicida subsp. salmonicida and revealed some genetic and biochemical variability. Logistic regression analyses showed that infection prevalence varied according to fish species/strain, year and gender, whereby Chinook salmon and females had the highest infection prevalence. Moreover, this pathogen was found in six fish species from eight sites, demonstrating its widespread nature within Michigan.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号