Ecology of the introduced snapper Lutjanus kasmiva (Forsskal) in the reef fish assemblage of a Hawaiian bay

Since its first introduction in 1955, the snapper Lutjanus kasmira (taape) has developed large populations in shallow coastal waters of Hawaii. Visual abundance estimates and trap catches of taape were different between the main habitat types of the reef. Overall, taape was the second most abundant species by numbers and biomass over a hard substratum and was patchily distributed, even within habitat type. The largest individuals occurred singly or in small groups on shallow reef slopes; on the deep slopes and in spur-and-groove habitat, taape occurred in larger groups of smaller sized fish. Catches in fish traps showed a negative relationship with the complexity of the adjacent natural substratum, suggesting that traps are more productive where they offer additional cover in areas with less natural cover. In all areas in which traps were used, from fringing reef to open sand, the catch was dominated by taape. Tagging confirmed the theory that taape tend to maintain a limited range over long periods. Tagging results also indicated occasional long-range movements among major habitats and provided data confirming patterns of movement between reef habitat by day and sand habitat by night. Taape collected over open sand substratum by trap and by hook-and-line were smaller than those collected by the same means at the reef. Observations and collections suggested an ontogenetic trend in habitat use by taape from initial settlement in fringe areas toward ultimate residence on the main reef. Other common fish species in the reef assemblages were tested for statistical associations with taape. Although several positive species associations were found, multivariate analysis did not reveal patterns that indicated strong ecological relationships.     

An intranuclear microsporidium associated with acute anemia in the chinook salmon, Oncorhynchus tshawytscha

An intranuclear microsporidium is described from hemoblastic cells of the chinook salmon, Oncorhynchus tshawytscha. The infection is associated with an acute anemia in the fish. Up to 47% of the hemoblast nuclei were infected in anemic fish. The organisms, found only in spleen and kidney tissues, were 1-2 microns in diameter and consisted of vegetative and early sporulation forms. This microsporidium differs from known species which parasitize fish in its tissue location; however, the absence of mature spores and other life cycle stages precludes determination of its precise taxonomic identity.     

Candidatus Renichlamydia lutjani, a Gram-negative bacterium in internal organs of blue-striped snapper Lutjanus kasmira from Hawaii

The blue-striped snapper Lutjanus kasmira (Perciformes, Lutjanidae) are cosmopolitan in the Indo-Pacific but were introduced into Oahu, Hawaii, USA, in the 1950s and have since colonized most of the archipelago. Studies of microparasites in blue-striped snappers from Hawaii revealed chlamydia-like organisms (CLO) infecting the spleen and kidney, characterized by intracellular basophilic granular inclusions containing Gram-negative and Gimenez-positive bacteria similar in appearance to epitheliocysts when seen under light microscopy. We provide molecular evidence that CLO are a new member of Chlamydiae, i.e. Candidatus Renichlamydia lutjani, that represents the first reported case of chlamydial infection in organs other than the gill in fishes.     

An Intranuclear Microsporidium Associated with Acute Anemia in the Chinook Salmon,Oncorhynchus tshawytscha1

An intranuclear microsporidium is described from hemoblastic cells of the chinook salmon, Oncorhynchus tshawytscha. The infection is associated with an acute anemia in the fish. Up to 47% of the hemoblast nuclei were infected in anemic fish. The organisms, found only in spleen and kidney tissues, were 1–2 μm in diameter and consisted of vegetative and early sporulation forms. This microsporidium differs from known species which parasitize fish in its tissue location; however, the absence of mature spores and other life cycle stages precludes determination of its precise taxonomic identity.     

Assemblage-level effects of the introduced peacock hind (<Emphasis Type="Italic">Cephalopholis argus</Emphasis>) on Hawaiian reef fishes

The peacock hind Cephalopholis argus (family Serranidae), locally known as ‘roi’, was introduced from French Polynesia to Hawaii in the mid-twentieth century as a food fish. However, because of its association with ciguatera fish poisoning, it is rarely fished for food. Previous research indicates that roi could have a negative impact on native reef fish assemblages because of their high densities and prey consumption rates. However, it is unclear whether roi add to the cumulative mortality of prey (predation hypothesis), or whether predation is instead compensatory (doomed surplus hypothesis). This study experimentally assessed the effects of roi on reef fish populations through a long-term (5.5 year) predator removal experiment. A Before-After-Control-Impact study design was used to assess changes in fish assemblages following the removal of roi on 1.3 ha of patch reef. Increases in the density of prey-sized fish (<15 cm TL) were observed 18 months after roi removal. However, those effects did not translate into sustained increases in prey. While increases in potential competitors, wrasses (family Labridae), particularly the piscivorous ringtail wrasse Oxycheilinus unifasciatus, were observed on roi-free reefs, the fish assemblage did not diverge substantially in composition. Native reef fish appeared to resist the potential negative impacts of predation by roi, possibly through a refuge in size for some fish families. Management to protect intact fish assemblage size-structure could serve to bolster native resistance to invading species. In considering the threats facing coral reefs, and the possible solutions, roi removal alone will not likely replenish native fishery resources.     

Disseminated visceral coccidiosis and cloacal cryptosporidiosis in a Japanese white-naped crane (Grus vipio)

A 4-mo-old male Japanese white-naped crane (Grus vipio) kept in an outdoor exhibit at the Everland Zoological Gardens in Korea became depressed and developed anorexia, weight loss, and diarrhea. Death of this bird was associated with an overwhelming systemic infection by an intracellular coccidian parasite, which resulted in necrosis and granulomatous inflammation in a number of major organs, including the intestine, liver, spleen, and kidney. Coccidian parasite-laden macrophages were commonly found in the blood vessels of these organs. Using electron microscopy and polymerase chain reaction assays, the parasite was identified as Eimeria sp. The bird was also infected with Cryptosporidium sp., which suggests an immunosuppressed state, although the cause of such suppression was not identified. Our findings suggest that an initial Eimeria sp. intestinal infection spread to other organs through the blood vessels, with the immunosuppressed state possibly contributing to a rapid hematogenous transmission. To our knowledge, this is the first report of disseminated visceral coccidiosis caused by Eimeria sp. in a captive Japanese white-naped crane.     

Prevalence and analysis of Renibacterium salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha in North Puget Sound

Renibacterium salmoninarum causes bacterial kidney disease (BKD), a chronic and sometimes fatal disease of salmon and trout that could lower fitness in populations with high prevalences of infection. Prevalence of R. salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha inhabiting neritic marine habitats in North Puget Sound, Washington, USA, was assessed in 2002 and 2003. Fish were collected by monthly surface trawl at 32 sites within 4 bays, and kidney infections were detected by a quantitative fluorescent antibody technique (qFAT). The sensitivity of the qFAT was within an order of magnitude of the quantitative real-time PCR (qPCR) sensitivity. Prevalence of infection was classified by fish origin (marked/hatchery vs. unmarked/likely natural spawn), month of capture, capture location and stock origin. The highest percentages of infected fish (63.5 to 63.8%) and the greatest infection severity were observed for fish collected in Bellingham Bay. The lowest percentages were found in Skagit Bay (11.4 to 13.5%); however, there was no difference in prevalence between marked and unmarked fish among the capture locations. The optimal logistic regression model of infection probabilities identified the capture location of Bellingham Bay as the strongest effect, and analysis of coded wire tagged (CWT) fish revealed that prevalence of infection was associated with the capture location and not with the originating stock. These results suggest that infections can occur during the early marine life stages of Chinook salmon that may be due to common reservoirs of infection or horizontal transmission among fish stocks.     

Susceptibility of juvenile Atlantic cod Gadus morhua to viral haemorrhagic septicaemia virus isolated from wild-caught Atlantic cod

A European strain of viral haemorrhagic septicaemia virus (VHSV) isolated from wild-caught cod Gadus morhua (H16/7/95) was shown to cause clinical disease and mortality in excess of 80% in juvenile Atlantic cod when administered by the intra-peritoneal (i.p.) route. No virus was recovered from cod cohabiting with experimentally infected fish at a ratio of 1:1, and no VHSV-associated mortality was demonstrated following immersion infection. External signs of disease in cod were the presence of exophthalmia and ascites. Virus was identified as VHSV by enzyme-linked immunosorbent assay (ELISA) and was recovered from both brain and organ pools (kidney, liver and spleen) of 100% of i.p. infected cod mortalities. Virus was also detected using an indirect immunofluorescence test on tissue imprints of kidney, liver, spleen and brain taken from moribund fish. The fact that cod were not susceptible to VHSV following waterborne exposure raises important questions surrounding the propagation, maintenance and impact of a naturally occurring reservoir of virus in the marine environment.     

A Piscirickettsia salmonis-like bacterium associated with mortality of white seabass Atractoscion nobilis

Mortality among hatchery-reared juvenile white seabass Atractoscion nobilis in southern California, USA, was associated with infections by a Piscirickettsia salmonis-like organism (WSPSLO). Infected fish had no consistent external signs other than pale gills, lethargy and impaired swimming behavior. Internally, the kidney and spleen were enlarged, and some fish had livers with multiple pale foci. Smears from infected kidney, liver, and spleen stained with Wright-Giemsa had intracytoplasmic coccoid organisms, often in pairs, that ranged in size from 0.5 to 1.0 microm. Microscopic lesions included multifocal hepatic, renal, and splenic necrosis, and intralesional macrophages often contained the WSPSLO. The bacterium was isolated from infected fish on cell lines of salmonid (CHSE-214) and white seabass (WSBK) origin. The WSPSLO induced plaque formation and destroyed the cell monolayers within 10 to 14 d incubation at temperatures of 15 and 20 degrees C. The bacterium retained infectivity for cell lines up to 14 d at 4 and 13 degrees C, up to 7 d at 20 degrees C, but it was inactivated at 37 and 56 degrees C within 24 and 1 h, respectively. Freezing at -20 degrees C reduced infectivity by 100-fold. Dehydration and resuspension in distilled water completely inactivated the bacterium. In contrast, the WSPSLO retained nearly all of its infectivity for CHSE-214 cells following a 72 h period in seawater at 20 degrees C. Polyclonal rabbit antibodies made to the WSPSLO reacted specifically in indirect fluorescent antibody tests (IFAT) with the bacterium in cell cultures and smears from infected fish tissues. Tissue smears from infected salmon or CHSE-214 cells with P. salmonis reacted weakly with the anti-WSPSLO serum. Conversely, polyclonal anti-P. salmonis serum produced a weakly positive reaction with the WSPSLO from infected CHSE-214 cells. The WSPSLO as propagated in CHSE-214 cells was highly virulent for juvenile coho salmon Oncorhynchus kisutch, inducing 80% mortality within 10 d of intraperitoneal injection of 10(2.5)-50% tissue culture infectious doses per fish. We conclude that the bacterium from white seabass possesses antigenic differences from P. salmonis yet possesses virulence for salmon equal to known strains of P. salmonis.     

The expression analysis of inflammatory and antimicrobial genes in the goldfish (Carassius auratus L.) infected with Trypanosoma carassii

We report results of a comprehensive analysis of inflammatory gene expression during the course of infection of Trypanosoma carassii in the goldfish. We observed significant increases in mRNA levels of genes encoding pro-inflammatory cytokines IFN-γ, TNFα1 and TNFα2; IL-1β-1 and IL-1β-2; IL-12-p35 and IL-12-p40; CCL1; CXCL8, anti-inflammatory cytokines IL-10 and TGFβ and iNOS A and iNOS B, using quantitative PCR. Expression levels and profiles of these cytokines and iNOS isoforms varied in the different tissues (kidney, spleen, liver) of goldfish during the course of T.?carassii infection. The expression of majority of genes that encode pro- and anti-inflammatory cytokines were up-regulated during the acute phase of infection (days 7-21 post-infection). The mRNA levels of these cytokines returned to normal levels or were down-regulated during the elimination phase of infection (days 28-56), with exception of IL-10 in the spleen and liver of infected fish. A parallel up-regulation of IFN-γ and IL-10 mRNA levels were observed in all tissues of infected fish during the acute phase of the infection. The expression of iNOS genes (iNOS A and B) was significantly delayed (day 14?pi) in the kidney, liver and spleen of infected fish. These results provide insights into the interaction between T.?carassii and goldfish, and suggest that Th1/Th2-like responses may be important for controlling T.?carassii infection in the goldfish.     

Quantitative and qualitative evaluation of iNOS expression in turbot (Psetta maxima) infected with Enteromyxum scophthalmi

Enteromyxum scophthalmi is the causative agent of turbot enteromyxosis, an intestinal parasitisation that produces severe desquamative enteritis leading to a cachectic syndrome and eventually the death. It is well known the importance of the innate immune response against parasites in fish, with the release of antimicrobial substances such as reactive oxygen and nitrogen species, produced by the inducible nitric oxide synthase (iNOS). This enzyme is mainly found in phagocytes, but also in structural cells from the intestinal mucosa. The aim of this study was to characterize iNOS in intestine and lymphohaematopoietic organs (spleen and anterior kidney) of turbot by means of immunohistochemistry in order to assess the possible changes of this enzyme through the infection. The presence of the enzyme was evaluated in control and E. scophthalmi-infected turbot. The results showed immunoreactivity in the apical border of enterocytes and mild staining of goblet cells in both control and infected turbot although it was more evident and widespread in infected turbot compared to control. Moderate numbers of iNOS+ cells were present in the lamina propria-submucosa of fish which presented moderate and severe inflammatory infiltrates at this level. In spleen and kidney, iNOS+ cells were scattered through the parenchyma and, in severely infected fish, tended to be allocated near the vascular structures and melano-macrophage centres. The number of positive cells at the lymphohaematopoietic organs was significantly higher in infected turbot and increased as infection progressed. The increase in the expression of iNOS in the tissues of E. scophthalmi-infected turbot was more evident in individuals with severer lesions. The measurement of the levels of iNOS during turbot enteromyxosis reveals a possibly delayed response that would not able to eliminate the parasites but would exacerbate mucosal injury.     

Response of Ig-positive cells to Enteromyxum scophthalmi (Myxozoa) experimental infection in turbot, Scophthalmus maximus (L.): A histopathological and immunohistochemical study

In recent years, a new parasite that causes severe losses has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis that affected all portions of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was set up to gain insights into the immune response of fish against this parasitic infection. The kinetics of immunoglobulin positive (Ig+) cells in spleen, kidney and intestine from turbot experimentally infected with E. scophthalmi was studied. For evaluating both the progress of infection and the lesions induced by the parasite, we performed histopathological studies and for detecting Ig+ cells in situ we used an indirect immunohistochemical method. In fish exposed to the parasite, the number of Ig+ cells significantly increased in the intestine, the target organ of the parasite, whereas in spleen and kidney, haematopoietic organs where the parasite was not detected, the number of Ig+ cells decreased. Furthermore, the pattern of distribution of Ig+ cells changed in all three organs examined in recipient/infected fish compared with control fish (not exposed to the parasite). The results obtained in this study indicate that the infection by E. scophthalmi in turbot induced an immune response that involved changes in the number and distribution of Ig+ cells.     

Parasites of coral reef fish larvae: its role in the pelagic larval stage

The pelagic larval stage is a critical component of the life cycle of most coral reef fishes, but the adaptive significance of this stage remains controversial. One hypothesis is that migrating through the pelagic environment reduces the risk a larval fish has of being parasitised. Most organisms interact with parasites, often with significant, detrimental consequences for the hosts. However, little is known about the parasites that larval fish have upon settlement, and the factors that affect the levels of parasitism. At settlement, coral reef fishes vary greatly in size and age (pelagic larval duration), which may influence the degree of parasitism. We identified and quantified the parasites of pre-settlement larvae from 44 species of coral reef fishes from the Great Barrier Reef and explored their relationship with host size and age at settlement, and phylogeny. Overall, less than 50% of the larval fishes were infected with parasites, and over 99% of these were endoparasites. A Bayesian phylogenetic regression was used to analyse host-parasite (presence and intensity) associations. The analysis showed parasite presence was not significantly related to fish size, and parasite intensity was not significantly related to fish age. A phylogenetic signal was detected for both parasite presence and intensity, indicating that, overall, closely related fish species were likely to have more similar susceptibility to parasites and similar levels of parasitism when compared to more distantly related species. The low prevalence of infection with any parasite type and the striking rarity of ectoparasites is consistent with the ‘parasite avoidance hypothesis’, which proposes that the pelagic phase of coral reef fishes results in reduced levels of parasitism.

     

Isolation and characterization of Pseudomonas sp. KUMS3 from Asian sea bass (Lates calcarifer) with fin rot

Bacteria were isolated from Asian Sea bass, Lates calcarifer kept in a farm, on the South-east coast of India. During an outbreak of fin rot, the affected fish had hemorrhages at the base of fins, mouth and skin muscles and faded pigments. Pure colonies were isolated on NA and ZMA from internal organs of the fish and the bacterial morphology was identified as gram-negative rod-shaped bacteria. Based on different biochemical tests and sequence of 16S rDNA, the causative bacteria were identified as Pseudomonas sp. KUMS3. Bacterial cells were isolated from liver and kidney of all artificially infected moribund fish and confirmed as Pseudomonas sp. KUMS3 by morphological and biochemical characteristics. During the experimental infection, the first incidence of dead fish was observed on 2nd day after exposure to Pseudomonas sp. KUMS3 and no fish died after 12 days post exposure and the cumulative percent of mortality was 70. Histological lesions were observed in the spleen, liver and kidney of the infected fish. Pseudomonas sp. KUMS3 could be considered as an opportunistic pathogen, which can survive on the fish surface or in water or in the gut and may cause disease when unfavorable conditions develop.     

Distribution,prevalence and severity of Parvicapsula minibicornis infections among anadromous salmonids in the Fraser River,British Columbia,Canada

Polymerase chain reaction (PCR) and microscopic examination of stained kidney sections were used to diagnose infections with the myxozoan parasite Parvicapsula minibicornis in maturing Fraser River salmon. In 2 series of collections, the parasite was detected in 109 of 406 migrating sockeye salmon Oncorhynchus nerka belonging to Early Stuart, Early Summer and Summer run-timing groups, mainly upper Fraser River stocks. However, the parasite was detected neither in fish at sea nor once they had migrated several 100 km upstream. Prevalence then increased to 95% or greater at the spawning grounds. Histological examination of kidney was less sensitive than PCR in detecting the parasite in salmon collected from the earliest sites in both collections found positive by PCR. Severity of infection was greatest at the spawning grounds. Development of infection in sockeye, measured by prevalence, severity or by the rate of false-negative histological diagnoses, appeared to be a useful estimate of in-river residence time. Prevalence and severity of infections in sequential samples of Harrison River and Weaver Creek sockeye stocks collected from the Harrison River indicated that more time had elapsed since parasite transmission than would be predicted based on migration distance alone. Pink salmon Oncorhynchus gorbuscha, coho salmon O. kisutch and chinook salmon O. tshawytscha were found to be infected with the parasite. Development of P. minibicornis in pink salmon was most similar to that in sockeye. Pink and coho salmon may be at risk to the pathological consequences of P. minibicornis infection.     

大亚湾人工鱼礁附着生物的初步研究

1988年8月至1989年7月在大亚湾鱼礁区进行附着生物调查研究,记录79种生物,大约有82.7％的生物种类是鱼礁区鱼虾的饵料生物(包括35种不带壳和32种带壳的饵料生物),有17.3％的生物种类为非饵料生物。礁区附着生物种类多,附着量大,生长迅速,投礁半年后100％被生物覆盖,附着厚度30mm,附着量达17.487kg/m~2。礁区生物一年四季都能繁殖附着,主要附着期4—10月,高峰期7、8、9三个月,是投礁的最佳时间。     

Pathogenicity of avian malaria in experimentally-infected Hawaii Amakihi

The introduction of avian malaria (Plasmodium relictum) and mosquitoes (Culex quinquefasciatus) to the Hawaiian Islands (USA) is believed to have played a major role in the decline and extinction of native Hawaiian honeycreepers (Drepanidinae). This introduced disease is thought to be one of the primary factors limiting recovery of honeycreepers at elevations below 1,200 m where native forest habitats are still relatively intact. One of the few remaining species of honeycreepers with a wide elevational distribution is the Hawaii Amakihi (Hernignathus virens). We measured morbidity and mortality in experimentally-infected Hawaii Amakihi that were captured in a high elevation, xeric habitat that is above the current range of the mosquito vector. Mortality among amakihi exposed to a single infective mosquito bite was 65% (13/20). All infected birds had significant declines in food consumption and a corresponding loss in body weight over the 60 day course of the experiment. Gross and microscopic lesions in birds that succumbed to malaria included enlargement and discoloration of the spleen and liver and parasitemias as high as 50% of circulating erythrocytes. Mortality in experimentally-infected amakihi was similar to that observed in Apapane (Himnatione sanguinea) and lower than that observed in Iiwi (Vestiaria coccinea) infected under similar conditions with the same parasite isolate. We conclude that the current elevational and geographic distribution of Hawaiian honeycreepers is determined by relative susceptibility to avian malaria.     

Mycobacteriosis in wild rabbitfish Siganus rivulatus associated with cage farming in the Gulf of Eilat, Red Sea

Infection patterns of Mycobacterium marinum were studied over a period of 3 yr in wild rabbitfish Siganus nivulatus populations associated with commercial mariculture cages and inhabiting various sites along the Israeli Red Sea coastline. Mycobacteriosis was first recorded from the Red Sea in 1990 in farmed sea bass Dicentrarchus labrax and is absent from records of studies on parasites and diseases of wild rabbitfish carried out in the 1970s and 1980s. A sharp increase in the prevalence of the disease in cultured and wild fish in the region has occurred since. A total of 1142 rabbitfish were examined over a 3 yr period from inside mariculture net cages, from the cage surroundings and from several sites along the coast. Histological sections of spleens were examined for presence of granulomatous lesions. Overall prevalence levels of 50% were recorded in the rabbitfish sampled inside the net cages and 39% at the cages' close surroundings, 21% at a sandy beach site 1.2 km westwards, 35% at Eilat harbour 3 km to the south and 42% at a coral reef site about 10 km south of the cages. In addition, 147 fish belonging to 18 native Red Sea species were sampled from 2 sites, the net cage farm perimeter and the coral reef area, and examined for similar lesions. None of those from the coral reef were infected with Mycobacterium; however, 9 of 14 species collected from the cage surroundings were infected. An increase in prevalence of mycobacteriosis in the mariculture farm area was noted from 1995 to 1997. At the same time, a significant increase in prevalence was also apparent at the coral reef sampling site. Two M. marinum isolates from rabbitfish captured at Eilat harbour and the coral reef site were shown by 16S rDNA sequencing analysis to be identical to isolates from rabbitfish trapped inside the mariculture cages as well as isolates from locally cultured sea bass D. labrax. The implications of spreading of M. marinum infection in wild fish populations in the Gulf of Eilat are discussed.     

Experimental susceptibility of turbot Scophthalmus maximus to viral haemorrhagic septicaemia virus isolated from cultivated turbot

Juvenile pathogen-free turbot were infected with a viral haemorrhagic septicaemia virus (VHSV) isolate recovered from turbot cultivated on the island of Gigha, West Scotland. Mortality of 100% was recorded in fish infected via the intra-peritoneal (i.p.) route. Horizontal transmission of VHSV in sea water was demonstrated by cohabitation of naive fish with i.p. infected fish at a ratio of 1:1. The total cumulative average mortality in cohabiting fish was 60% by 60 d post-infection. Turbot infected via an immersion route exhibited a cumulative average mortality of 71% by the end of the experiment. VHSV identified by enzyme-linked immunosorbent assay (ELISA) was recovered from both organ (kidney and spleen) and brain samples of individual fish that died following infection by all experimental routes. These findings pose significant implications regarding the persistence of VHSV and its role in limiting natural populations of marine fish species. In addition, the establishment of infection models for the transmission of VHSV in sea water is of fundamental importance to the development of anti-VHSV vaccines in important commercial species such as turbot.     

蟹栖异阿脑虫寄生大菱鲆及其组织病理学研究

论文首次报道了蟹栖异阿脑虫(Mesanophrys carcini)在养殖大菱鲆体内的寄生情况以及所引起宿主的组织病理学变化。观察结果表明,感染的苗期大菱鲆的大部分器官组织包括皮肤、鳍、鳃、眼、脑、心脏、肝脏、肾脏、脾脏、胰腺和消化道等以及器官组织间隙中都发现了寄生的蟹栖异阿脑虫,属于全身性感染;而对于成鱼,蟹栖异阿脑虫主要寄生于皮肤、鳍和鳃等器官组织;严重感染者,蟹栖异阿脑虫可侵入其脑、肝脏、肾脏和心脏等器官组织,但数量不多。蟹栖异阿脑虫在大菱鲆体内的寄生能够引起病鱼各器官组织发生不同程度的组织病理学改变。该病在幼鱼和成鱼身上所表现出较一致的病理学特征为:鳃小叶呼吸上皮细胞增生;脑膜炎和脑组织液化性坏死;肾脏和脾脏造血组织坏死;肝脏中央静脉和窦状隙扩张;肌纤维发生凝固性坏死和眼的脉络膜充血、水肿;单核巨噬细胞浸润。研究认为,蟹栖异阿脑虫寄生引起的鳃损害使病鱼呼吸困难,窒息是病鱼发生死亡的主要原因,而虫体寄生导致的各器官组织变性,坏死,使得病鱼器官功能衰竭可加速鱼的死亡。另外,文中还探讨了蟹栖异阿脑虫入侵大菱鲆的可能途径,认为破损的皮肤和鳃是入侵的主要途径。研究结果告诉我们,在大菱鲆养殖过程中防止鱼体擦伤,保持池底清洁对于预防疾病的发生非常重要;对该病的治疗应采取外部杀虫和内部口服药物相结合的方式。