Showing papers in "Journal of Fish Diseases in 1990"
TL;DR: An insoluble polysaccharide from the cell wall of Saccharomyces cerevisiae, called M-Glucan, has been shown to enhance the non-specific disease resistance of Atlantic salmon when injected intraperitoneally.
Abstract: . An insoluble polysaccharide from the cell wall of Saccharomyces cerevisiae, called M-Glucan, has been shown to enhance the non-specific disease resistance of Atlantic salmon, Salmo salar L., when injected intraperitoneally. M-Glucan consists only of glucose units which presumably are linked through β-1,3 and β-1,6 linkages. Enhanced resistance was demonstrated against Yersinia ruckeri, the causal agent of enteric redmouth disease, against Vibrio anguillarum, the causal agent of classical vibriosis and against Vibrio salmonicida, which causes cold water vibriosis or ‘Hitra-disease’ in salmon. At a dose of 2mg M-Glucan per fish (20g mean weight), maximal resistance developed in the fish 3 weeks after injection. Injection of different glucan doses and challenge one week later with Vibrio anguillarum, showed that 50-200μg glucan per fish resulted in the highest level of resistance. The level of resistance in Atlantic salmon obtained with M-Glucan was strikingly higher than that obtained with another glucan which was prepared from Saccharomyces cerevisiae by a different procedure.
293 citations
TL;DR: Light and electron microscopic examinations showed that the only consistent histopathological feature was extensive nervous necrosis in the spinal cord, spinal ganglia and brain of hatchery-reared Japanese parrotfish larvae and juveniles.
Abstract: . Mass mortalities of hatchery-reared Japanese parrotfish larvae and juveniles, Oplegnathus fasciatus (Temminck & Schlegel), have occurred in Nagasaki Prefecture. Light and electron microscopic examinations showed that the only consistent histopathological feature was extensive nervous necrosis in the spinal cord, spinal ganglia and brain. Numerous non-enveloped virus particles, icosahedral in morphology and measuring about 34 nm in diameter, were found in the cytoplasm of affected neurones and glial cells. Such nervous necrosis is believed to be the major cause of the mass mortalities of hatchery-reared Japanese parrotfish larvae and juveniles.
230 citations
193 citations
TL;DR: The response of fish vaccinated with live parasites indicates that animals injected intraperitoneally can develop surface immunity and that i.p. injeetion is a suitable route of administratio n for potential /.
Abstract: Fish surviving infection with the pathogenic ciliated protozoan, Ichthyophthirius multifiliis (Fouquet. 1876), become resistant to subsequent infection by the parasite. The acquired immunity suggests that development of a vaccine against the parasite may be possible. Because of the advantages of immunoprophyl axis for treatment of the disease, an effort has been made to determine whether fish exposed to killed parasite preparations ean resist subsequent lethal challenge. Both the route of administratio n and the effeets of stage speeifie antigens have been examined. Channel catfish vaeeinated by intraperitone al (i.p.) injeetion or bath immersion with killed /. muhifiliis tomites show 100% mortality following a standard challenge protocol. Similarly, 100% mortahty was observed in test groups injeeted with tomite cilia. In both cases, a consistent differcnee in days to death between eontrol and test group animals was observed. Although eomplete mortality was seen with fish injected with tomite preparations, fish vaceinated with killed trophonts (the feeding stage of the parasite) had a mueh greater degree of protection with approximately 50% of fish surviving an otherwise lethal ehallenge. Finally, animals injected intraperitoneally with live tomites showed nearly eomplete immunity and were identieal in their response to fish whieh survive natural infeetion. The response of fish vaccinated with live parasites indicates that animals injected intraperitoneally can develop surface immunity and that i.p. injeetion is a suitable route of administratio n for potential /. multifiliis vaeeines.
91 citations
TL;DR: Atlantic salmon infected with juvenile stages of Lepeophtheirus salmonis were obtained from sea loch cage sites on the West coast of Scotland and attached parasites on the skin were studied using light and electron microscopy.
Abstract: . Atlantic salmon infected with juvenile stages of Lepeophtheirus salmonis were obtained from sea loch cage sites on the West coast of Scotland. Attached parasites on the skin were studied using light and electron microscopy. Behavioural activity was observed in attached stages maintained on skin in vitro. Pathological changes were associated with four main areas of interaction between the parasite and the host, namely second antennal attachment, filament attachment, maxilliped activity and feeding activity. The skin changes involved were initial mechanical disruption followed by epidermal hyperplasia. The filament material was secreted into the epidermis and spread laterally without breaching the basement membrane. Surprisingly little reaction to the filament occurred, but chalimus activity resulted in chronic changes which were more marked as the later chalimus stages were reached. Fibroplasia was a feature of lesions induced by redundant filaments resulting in small nodular lesions. After erosion of these nodules, all that remained were the melanized rings characteristic of old chalimus sites.
88 citations
86 citations
TL;DR: In this article, a Juvenile carp, Cyprinus carpio L., was immunized against I multifiliis following controlled exposure to the infective theront stage, and injected with either triamcinolone acetonide or hydrocortisone 21-hemisuccinate at doses of 100 μg or 10 μg/g body weight.
Abstract: . Juvenile carp, Cyprinus carpio L., were immunized against Ichthyophthirius multifiliis following controlled exposure to the infective theront stage. On challenge, with a potentially lethal dose of theronts, all immunized fish survived, in contrast to 100% mortality in non-immunized fish. Fourteen days following exposure to the challenge infection, immune and non-immune fish were injected intraperitoneally with either triamcinolone acetonide or hydrocortisone 21-hemisuccinate (cortisol) at doses of 100 μg or 10 μg/g body weight. Controls, including immunized and non-immunized fish, were injected with saline or left untreated. Six days following corticosteroid administration, fish were exposed to challenge infections of I multifiliis. All fish treated with corticosteroid developed heavy infections with up to 100% mortality. Repeat experiments gave comparable results. Serum antibody levels recorded in similarly treated fish at intervals of 12 h and/or 1 week following corticosteroid administration were found to be relatively unaffected. The results are discussed in relation to the immune response to I multifiliis.
75 citations
74 citations
TL;DR: It is hypothesized that trypsin in mucus-secreting cell layers of Atlantic salmon is a part of the non-specific immune defence of the fish.
Abstract: . Immunohistochcmical examination showed that trypsin was present in mucus-secreting cell layers of Atlantic salmon, such as surface epithelial cells of gills and intestine, and epidermal cells of dorsal skin. Trypsin in tissue slices was identified by an immunohisto-chemical technique which used affinity purified immunoglobulins from rabbit antisera against purified salmon pancreatic trypsin as primary antibodies. Most of the positively stained cells appeared to be granulated and secretory. The authors hypothesize that trypsin in mucus-secreting cell layers is a part of the non-specific immune defence of the fish.
65 citations
TL;DR: An antibody–dependent cell–mediated cytotoxic (ADCC) mechanism is proposed, conferring protection in immunized fish, supported by the finding that cercarial and diplostomule antigens are capable of activating macrophages in Immunized rainbow trout.
Abstract: . The degree of protection in immunized rainbow trout against the infective larval stages of Diplostomum spathaceum was investigated. Immunized rainbow trout demonstrated a 70–80% reduction in the number of metacercariae establishing in their eye-lenses following challenge with live cercariae compared with unimmunized fish. Both normal trout serum and anti–diplostomule serum weTC cytotoxic to diplostomules in vitro. However, there was no correlation between the degree of protection and the level of serum antibody within individual fish. Reduced establishment of migrating diplostomules, indicative of in vivo killing, occurred in fish possessing activated macrophages and challenged with cercariae opsonized with specific antibody. An antibody–dependent cell–mediated cytotoxic (ADCC) mechanism is proposed, conferring protection in immunized fish. This is supported by the finding that cercarial and diplostomule antigens are capable of activating macrophages in immunized rainbow trout. The role of macrophage activation and specific antibody in conferring protection in immunized fish is discussed.
55 citations
TL;DR: Eggs were relatively resistant to these chemicals; however, trichlorfon and praziquantel were the most effective in killing eggs.
Abstract: . Monogeneans of the superfamily Capsaloidea have been a severe problem in maintaining both teleosts and elasmobranchs in captivity. Infestations of Benedeniella posterocolpa on the skin of the cownose ray, Rhinoptera bonasus, provided an excellent model for testing the effects of trichlorfon (0-7ppm), praziquantel (20ppm) and copper sulphate (0-25 ppm) on adult monogeneans in situ, and on adult monogeneans, oncomiracidia and eggs in vitro. One treatment with praziquantel eliminated 100% of the worms from the skin of rays. Two treatments with trichlorfon only eliminated 81% of the worms. Praziquantel killed all worms tested in vitro within 6h and prevented egg deposition. Trichlorfon killed all worms within 21 h, but some eggs were deposited. Copper sulphate had little effect on worms in vitro. Both trichlorfon and praziquantcl immobilized oncomiracidia while copper sulphate had little effect. Eggs were relatively resistant to these chemicals; however, trichlorfon and praziquantel were the most effective in killing eggs.
TL;DR: A new myxosporean, Sphaerospora testicularis sp.
Abstract: . A new myxosporean, Sphaerospora testicularis sp. nov., was found in fresh smears from the organs of wild and cultured sea bass, Dicentrarchus labrax (L.), and seminal fluid from spermiating cultured males. It is distinguished from all previously reported Sphaerospora spp, by the shape and dimensions of the mature spore, its location and the host and its geographical distribution. Only males were parasitized; 2.5% of the wild fish and 6-25% of the cultured fish were infected. In spermiating cultured males, the prevalence of infection increased progressively from 6-9 to 75% during the study period. The parasite causes destruction of the tubular tissue of testes and a reduction or loss of spermatozoa.
TL;DR: In vivo infectivity studies provided no evidence for the existence of unculturable but infective forms of A. salmonicida subsp.
Abstract: . The survival of Aeromonas salmonicida subsp. salmonicida was investigated in sea water under a variety of conditions. Survival in different types of microcosms (glass or dialysis bags); of bacteria grown under both in vivo and in vitro (broth culture) conditions; and in sterile and non-sterile sea water were compared. In all cases, survival was found to be of short duration (<10 days) and did not conflict with the previously stated obligate nature of the pathogen. The spread of furunculosis may depend less on its ability to survive in the environment than on its rate of shedding from infected fish and prevailing hydrographic conditions. Survival was extended and growth occurred in sterile sea water to which nutrients (tryptone soya broth) had been added. However, sea water obtained from beneath a commercial salmon cage, which would have been expected to be nutrient rich, did not prolong the survival of the pathogen. In vivo infectivity studies provided no evidence for the existence of unculturable but infective forms of A. salmonicida subsp. salmonicida which, therefore, validates the use of colony-forming units as a measure of survival.
TL;DR: Common carp were experimentally infected with cloned Trypanoplasma borreli and some haematological data were determined, and differential blood cell counts showed an increased abundance of leucocytes, especially granuloblasts and granulocytes.
Abstract: . Common carp, Cyprinus carpio L., were experimentally infected with cloned Trypanoplasma borreli and some haematological data were determined. The haematocrit and total erythrocyte counts were reduced and were lowest at day 29 post-inoculation during the peak of infection. Differential erythrocyte number showed a reduction in mature erythrocytes and an increase in immature erythrocytes. The total leucocyte number was markedly increased and peaked at day 44 post-inoculation. Differential blood cell counts showed an increased abundance of leucocytes, especially granuloblasts and granulocytes.
TL;DR: It is suggested that, if no naive fish are introduced into a closed system for a period (and this has to be determined under field conditions) after an outbreak, then there will be no infective larvae in the water and the system will now be safe for restocking.
Abstract: . All recovered and naive Helostoma temmincki lost their infections 30 days after homologous challenge with Lernaea cyprinacea. It is suggested that there is acquired protective immunity in recovered fish. No parasites were detected in five out of 20 recovered fish when the infective challenge dose was low; all naive fish (20) in the same tank were infected. In another experiment, all nine recovered fish were infected when the challenge infective dose was high. Recovered fish lost their infections (i.e. number of fish with no parasites and the number of parasites rejected) much faster than naive fish and this was very evident in the first 2 weeks after challenge. Parasites on recovered fish lost more egg sacs than naive fish during the same period. Eggs from parasites on recovered fish either did not hatch or were not infective or only caused a very low transitory infection in naive fish. It is suggested that, if no naive fish are introduced into a closed system for a period (and this has to be determined under field conditions) after an outbreak, then there will be no infective larvae in the water and the system will now be safe for restocking. This novel approach to control of the parasite L. cyprinacea and the spread of this disease will have to be carefully tested under field conditions.
TL;DR: The occurrence of a typical DTH reaction in rainbow trout and the feasibility of assessing it by measuring the thickness of the induration provides a simple and practical method for assessing cell-mediated immunity in large scale vaccination programmes against pathogens.
Abstract: . Delayed-type hypersensitivity (DTH) reaction (an in vivo manifestation of cell-mediated immunity) was detected in Oncorhynchus mykiss maintained on a pantothenic-acid-supplemented diet 2 weeks after infection with Cryptobia salmositica. The reaction was similar to that in mammals with mononuclear cell infiltration into the dermis and muscle layers and the presence of oedema. DTH reaction was also displayed by fish on a pantothcnic-acid-supplemented diet that had recovered from the infection and were protected against further infection. The reaction was less marked in infected or protected fish on a pantothenie-acid-deficient diet. Inhibition of macrophage migration (an in vitro expression of cell-mediated immunity) was observed when head kidney cell suspensions from protected fish maintained on either pantothenic acid supplemented or deficient diets were incubated with Cryptobia antigen. No inhibition of migration was evident when head kidney cell suspensions from the above fish were incubated without antigen, nor was it evident when cells from uninfected fish were used. The occurrence of a typical DTH reaction in rainbow trout and the feasibility of assessing it by measuring the thickness of the induration provides a simple and practical method for assessing cell-mediated immunity in large scale vaccination programmes against pathogens.
TL;DR: Cell surface characteristics indicated that most virulent strains agglutinated in the presence of acriflavine, but not all sedimented after boiling, whereas both virulent and avirulent strains had in vitro epithelial cell adhesive capabilities.
Abstract: . Motile Aeromonas spp. virulent for fish were studied with regard to their adhesion profile. Electron microscopy demonstrated the presence of fimbriae (pili) on Aeromonas cells regardless of virulence potential. The results show no significant correlations between ability to haemagglutinate, yeast cell co-agglutination and virulence. All strains expressed mannose-sensitive haemagglutinin activity against guinea pig erythrocytes. Using four types of red blood cells no characteristic haemagglutinin pattern related to virulence could be discerned. Expression of surface haemagglutin(s) on Aeromonas hydrophila appears to be medium dependent; strains grown in liquid media demonstrated enhanced haemagglutination activity. Both virulent and avirulent strains had in vitro epithelial cell adhesive capabilities. Cell surface characteristics measured by agglutination in acriflavine and stability after boiling indicated that most virulent strains agglutinated in the presence of acriflavine, but not all sedimented after boiling. The ability of 10 selected strains of A hydrophila to grow in normal pooled catfish serum was determined. Only 17% of the virulence variations can be explained by their sensitivity to serum.
TL;DR: The results demonstrate that Atlantic salmon has a humoral immune system capable of producing antibodies which discriminate between related bacterial antigens and between different serotypes of a virus.
Abstract: . Atlantic salmon, Salmo salar L., responded to intraperitoneal injection of formalin killed Vibrio salmonicida or live infectious pancreatic necrosis virus (ipnv) by producing specific antibodies. The antibody titre varied significantly within the group tested. Western blot analysis demonstrated that high-titre antisera recognized two major bacterial antigens with molecular weights of 12–15 kD and 22–27 kD. In addition, a few narrow bands with higher molecular weights were observed. An antiserum raised against IPNV recognised two major antigens corresponding to the structural proteins of the virus. Elisa and Western blot analysis showed that the immune serum raised against Vibrio salmonicida reacted slightly with Vibrio anguillarum, whereas no reaction to Yersinia ruckeri or Aeromonas salmonicida was detected. Indirect elisa and an elisa competition assay revealed that the immune serum raised against the N1 serotype was specific for this serotype of ipnv. The results demonstrate that Atlantic salmon has a humoral immune system capable of producing antibodies which discriminate between related bacterial antigens and between different serotypes of a virus.
TL;DR: The gross and histopathological appearance as well as the bacteriological findings in an outbreak of panophthalmitis in farmed chinook salmon suggest that the localization to the eye was not incidental, but a specific tropism.
Abstract: . This report describes the gross and histopathological appearance as well as the bacteriological findings in an outbreak of panophthalmitis in farmed chinook salmon. In all cases, the bacteria were either Mycobacterium neoaurum or an unidentified Rhodococcus spp.; in some fish, both types were present in roughly equal numbers, while in others, one type dominated. Despite occasionally recovering the bacteria from kidney or spleen, no lesions were found in these or in any other organ, suggesting that the localization to the eye was not incidental, but a specific tropism. Nevertheless, the possibility of predisposing cause(s) must be considered and these are discussed.
TL;DR: The results strongly suggest that the VS-P1 antigen is a complex of both protein and LPS molecules.
Abstract: . Outer membranes and lipopolysaccharides of the marine fish pathogens Vibrio salmonicida and Vibrio anguillarum were isolated. SDS-PAGE profiles of purified LPS preparations from V. salmonicida revealed a broad low molecular weight band, whereas V. anguillarum LPS profiles demonstrated both a low-molecular band and several weaker high-molecular weight bands. Hydrolysis of V, salmonicida and V. anguillarum LPS separating the polysaccharide chain from the lipid A part and subsequent gel-chromatography suggests a polysaccharide molecular weight of ca. 1000 (‘rough type’ LPS) and ca. 6000 ('smooth type’ LPS), respectively. Western blot of V. salmonicida outer membrane preparations and purified lipopolysaccharides and subsequent immunostaining with mouse monoclonal antibodies was performed. Eleven out of 15 monoclonal antibodies made against V. salmonicida cells reacted with one broad antigen-band in the low molecular weight region of both outer membrane and LPS profiles, corresponding to the LPS region. The previously reported outer surface antigen, VS-P1 from V. salmonicida, was observed to carry LPS epitopes as revealed by binding of monoclonal antibodies to VS-P1 as well as purified LPS preparations. These results strongly suggest that the VS-P1 antigen is a complex of both protein and LPS molecules.
TL;DR: In this article, a bacterin produced with this strain by Rhone-Merieux has been tested in both species and, as a comparison, by intraperitoneal injection.
Abstract: . Turbot, Scophthalmus maximus (L.), and sea bass, Dicentrarchus labrax (L.), are susceptible to vibriosis, a septicaemia caused in France by Vibrio anguillarum 408. A bacterin produced with this strain by Rhone–Merieux has been tested orally in both species and, as a comparison, by intraperitoneal injection. During a challenge carried out 4 weeks later by intraperitoneal inoculation, the protection observed in orally vaccinated fishes was significant (72 % in sea bass and 70 % in turbot). Eleven weeks after vaccination, this protection is still significant. The mean titre of serum agglutinins was weakly increased in orally vaccinated fishes. Bacteriostatic antibodies have also been searched for in serum, but compared to agglutination, the applied technique leads to lower titres and it has not been possible to prove the presence of such antibodies after oral vaccination. Passive immunizations using serum from orally vaccinated fishes (2 months after vaccination) confers some protection against a challenge carried out by inoculation of virulent vibrio. Therefore, the production of serum factors following oral vaccination of sea bass and turbot may be involved in generalized protection of fish.
TL;DR: During 1988, Serratia liquefaciens was recognised as a pathogen of Atlantic salmon in two marine cage sites within Scotland and the antagonistic interactions of the pathogen with native aquatic bacterial communities has been examined.
Abstract: During 1988, Serratia liquefaciens was recognised as a pathogen of Atlantic salmon, Salmo salar L., in two marine cage sites within Scotland (Mclntosh & Austin 1990). The antagonistic interactions of the pathogen with native aquatic bacterial communities has been examined. From this study, inhibitory bacteria were recovered and the inhibitory mechanism(s) investigated. Approximately 10 1 of sea water, together with marine algae (namely Fueus and Laminaria) and sediment were collected during October 1988, at lm below the low tide mark, at South Queensferry which is located on the Firth of Forth, near Edinburgh, Scotland. The samples were returned to the laboratory and transferred to a 20-1 capacity glass tank equipped with an aeration system. At the time of sampling, the temperature and salinity of the water were 10°C and 29%o, respectively. A 20-cm length of 2-cm-wide dialysis tubing was filled with a suspension (10** cells/ml) in marine salts solution (MSS; Austin, Allen, Zachary, Belas & Colwell 1979) of S. liquefaciens (strain K2; Mclntosh & Austin 1990). This tubing was suspended in the glass tank containing the marine samples. Preliminary experiments indicated that this technique permitted metabolites to leach out from the organisms inside the dialysis tubing, attracting inhibitory members of the aquatic microbial community. These organisms colonized the outside wall of the dialysis tubing. Water was collected at intervals of 0, 24, 48 and 72 h from the wall and at 1and 30-cm distances from the dialysis tubing. The samples were diluted to lO\"'* in MSS, and 0-1-ml volumes spread over the surface of triphcate plates of a basal marine agar (BMA; 0-1% [w/v] glucose, 4-0% [w/v] ammonium chloride, 2% [w/v] TRIS hydrochloride, 1% [w/v] agar No. 1 [Oxoid], prepared in MSS; pH 7-5) with incubation aerobically at 25''C for up to 7 days. Then, an assortment of colonies was picked randomly and examined for antagonism to S. liquefaciens. Thus, BMA plates were inoculated with two parallel streaks of the S. liquefaciens culture, approximately 10cm apart. These plates were incubated at 25°C for 1 h to allow the pathogen to stabilize with the new environment and to permit the surface of the medium to dry properly. Then, a total of 280 pure cultures, from the initial dilution plates, were streaked at right angles (10 colonies per plate) across the lines of inoculum of S. liquefaciens. Inoculated media were incubated at 25'̂ C for up to 72h, whereupon the interruption of growth of S. liquefaciens in the vicinity of the environmental isolates was scored as inhibition. Inhibitory
TL;DR: Certain deficient diets are useful in modulating the parasitaemia and also in decreasing red cell destruction, and dietary modification may help in altering the course of such infections and the progression of the disease.
Abstract: . The humoral immune response in Cryptobia-salmositica-infected rainbow trout on pantothenic-acid-deficient/low protein (19%) diets was depressed. There was no significant difference in parasitaemia between fish on the pantothenic-acid-deficient diet and those on the supplemented diet; however, the parasitaemia in fish on 19% protein diet was significantly lower than that in fish on 38% protein diet. The low humoral responders, in contrast to the high responders (on 38 and 29% protein diets), had less severe anaemia and the packed cell volume at the end of the experiment was not significantly different from that at 2 weeks post-infection. Red cells from the low responders were Coombs’ negative while those from the high responders were Coombs’ positive from 4 to 6 weeks post-infection. The authors suggest that, in the low responders, red cell destruction is essentially due to the‘lytic component’ of the parasite antigen in contrast to the involvement of both the llytic’ and the ‘immune complex-forming’ components in the high responders. The present study indicates that certain deficient diets are useful in modulating the parasitaemia and also in decreasing red cell destruction. Therefore, dietary modification may help in altering the course of such infections and the progression of the disease.
TL;DR: For the strains examined, neither autoagglutination nor X-protein were reliable indicators of virulence, and absence of A-protein did not necessarily mean avirulence.
Abstract: . Twelve Aeromonas salmonicida isolates were examined for autoagglutination, colony colour on tryptone soy agar supplemented with Coomassie brilliant blue (TSA-C), and outer membrane protein pattern by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Autoagglutination did not correlate with colony colour on TSA-C, nor with the presence of the additional 49-kDa protein (A-protein) in all strains tested. However, there was a correlation between colour on TSA-C and A-protein. Two weakly autoagglutinating isolates with no A-protein detectable in SDS-PAGE and with negative staining behaviour on TSA-C shared another additional protein, designated X-protein. One of these isolates was virulent for juvenile rainbow trout, the other one avirulent. Thus, for the strains examined, neither autoagglutination nor X-protein were reliable indicators of virulence, and absence of A-protein did not necessarily mean avirulence.
TL;DR: The susceptibility of sablefish, Anoplopoma fimbria (Pallas), a potential candidate for commercial mariculture, to the devastating salmonid pathogen Renibacterium salmoninarum and the pathology of the infection were investigated and the implication of the findings to the operation of salmon marinefarms is discussed.
Abstract: . The susceptibility of sablefish, Anoplopoma fimbria (Pallas), a potential candidate for commercial mariculture, to the devastating salmonid pathogen Renibacterium salmoninarum (Rs) and the pathology of the infection were investigated. Sablefish became moribund or died of apparently uncomplicated infections of Rs within 50-71 days following intrapcritoncal inoculation of the pathogen and pure cultures of Rs were re-isolated from some affected individuals. At least one sablefish carried the pathogen up to 165 days post-inoculation when the experiment was terminated. The pathology of the Rs infection in this strictly marine fish is described and the implication of the findings to the operation of salmon marinefarms is discussed.
TL;DR: The microsporidian Pleistophora senegalensis sp.
Abstract: . The microsporidian Pleistophora senegalensis sp. nov. parasitizes the gilt-head sea bream, Sparus aurata L, The parasite is found in the intestinal wall where it forms small xenomas in the muscularis. The development cycle of this species is described by light and electron microscopy. Meronts are rounded plasmodia dividing by plasmotomy and bounded by an amorphous and very regular wall. At the onset of sporogony, sporophorous vesicles are formed by separation of the plasma membrane from the external wall which then becomes a characteristic mesh. Mature spores (4.45 × 2.37μm) are ovoid and slightly pyriform with a large posterior vacuole.