Download Pathology of Edwardsiella tarda infection in turbot, Scophthalmus

Journal of Fish Diseases 2006, 29, 87–94
Pathology of Edwardsiella tarda infection in turbot,
Scophthalmus maximus (L.)
F Padrs1, C Zarza2, L Dopazo1, M Cuadrado1 and S Crespo1
1 Servei de Diagnòstic Patològic en Peixos and Centre de Referència i Desenvolupament en Aqüicultura (Generalitat de
Catalunya), Departament de Biologia Animal, de Biologia Vegetal i d’Ecologia, Facultat de Veterinària, Universitat
Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Barcelona, Spain
2 Skretting, Carretera de la estación s/n, Cojóbar, Burgos, Spain
Abstract
Macroscopic and histopathological changes in cultured turbot, Scophthalmus maximus (L.), in Spain
caused by infection with Edwardsiella tarda are
described. Eye tumefaction, inflammation, haemorrhages, ascites and the presence of a purulent
fluid were the main macroscopic lesions observed.
Histopathological lesions were found in the kidney,
spleen and liver. In the kidney and spleen these were
characterized by a severe apostematous inflammatory reaction, with a large number of abscesses. The
liver was affected to a lesser degree and only some
phagocytes loaded with bacteria were observed.
Ultrastructural observations indicated that macrophages were the main cell type implicated in the
inflammatory response. Most of the bacteria
observed within the phagocyte cytoplasm showed
no degenerative changes and some were dividing.
Degenerative changes observed in macrophages
indicate their failure in preventing the infection.
Keywords: Edwardsiella tarda, histopathology,
infection, Scophthalmus maximus, Spain, turbot.
Introduction
In the recent years, the number of bacterial
pathogens described in turbot, Scophthalmus maximus (L.), has increased substantially. Vibriosis
Correspondence Dr F Padrós, Servei de Diagnòstic
Patològic en Peixos, Facultat de Veterinaria, Universitat
Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès),
Barcelona, Spain
(e-mail: [email protected])
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caused by Listonella anguillarum (formerly Vibrio
anguillarum) was one of the first bacterial diseases
described in this species (Horne, Richards, Roberts
& Smith 1977; Devesa, Toranzo & Barja 1985).
Although it is still a major problem for turbot
culture, the number of cases and the severity of
outbreaks are controlled by systematic vaccination
programmes in most turbot farms. Outbreaks by
Streptococcus parauberis were described in the
mid-1990s (Toranzo, Devesa, Heinen, Riaza,
Núñez & Barja 1994; Doménech, FernándezGarayzabal, Pascual, Garcı́a, Cutuli, Moreno,
Collins & Domı́nguez 1996) which caused severe
problems until an effective vaccine was developed.
More recently, other emerging problems such as
flexibacteriosis caused by Tenacibaculum maritimum (Alsina & Blanch 1993; Pazos, Santos,
Núñez & Toranzo 1993) and furunculosis caused
by Aeromonas salmonicida (Nougayrede, Sochon &
Vuillaume 1990; Pedersen, Kofod, Dalsgaard &
Larsen 1994) have caused significant losses in
turbot farms. Other bacterial diseases, such as
vibriosis due to Vibrio alginolyticus (Austin, Stobie,
Robertson, Glass, Stark & Mudarris 1993) and
Photobacterium damselae subsp. damselae (formerly
Vibrio damsela) (Fouz, Larsen & Toranzo 1991;
Fouz, Larsen, Nielsen, Barja & Toranzo 1992)
and infections of Serratia liquefaciens (Vigneulle &
Baudin Laurencin 1995) have been recorded,
mostly as isolated cases and not as epizootic
diseases. In 1994, the first isolation of Edwardsiella
tarda was described in turbot (Nougayrede,
Vuillaume, Vigneulle, Faivre, Luengo & Delprat
1994). Since this first description other cases have
been reported in Spanish farms.
Journal of Fish Diseases 2006, 29, 87–94
Infections by Edwardsiella have been described in a
wide range of species (Plumb 1993). In the 1980s,
edwardsiellosis caused by E. tarda was shown to be
responsible for significant losses in the Japanese
flounder, Paralichthys olivaceus (Temminck & Schlegel), and the disease has become one of the most
important problems in farming of the species (Kusuda
& Kawai 1998). Therefore, edwardsiellosis is an
important potential threat to turbot farming. The
aim of the present study was to describe the pathological
findings observed in turbot infected by E. tarda and to
compare them with cases of edwardsiellosis in other fish
species and with other bacterial infections in turbot.
Materials and methods
Fish
A clinical case of edwardsiellosis caused by E. tarda
was described in Autumn 2003 in a turbot farm
situated in the Gulf of Biscay (Atlantic Coast of
Spain). The outbreak affected several batches of fish
during October and November. Water temperatures
ranged between 15.2 and 17.7 °C during this period. Fish were reared at a density of 30–40 kg m)2.
Market-size fish (900–1200 g) were mainly affected
and total cumulative mortality on the farm was 3%,
but in some tanks it was up to 10%. Diseased turbot
were microbiologically sampled. A complete necropsy was carried out and imprints of the kidney,
liver and spleen were taken and Gram stained.
Histopathology
Samples of the kidney, liver and spleen were fixed in
10% phosphate-buffered formalin, dehydrated in
an ethanol series and embedded in paraffin.
Sections (3–4 lm) were stained with haematoxylin
and eosin (H&E), Giemsa and Gram stains.
For transmission electron microscopy, samples of
kidney, spleen and liver were fixed in 2% buffered
glutaraldehyde (pH 7.4), post-fixed with 1%
osmium tetroxide, stained Ôen blocÕ with uranyl
acetate, dehydrated and embedded in Epon. Sections
were stained with 1% lead citrate and examined with
a Hitachi H-7000 electron microscope (Hitachi,
Tokyo, Japan).
Microbiology
Samples of the liver, spleen and kidney were
streaked onto trypticase-soy agar and Columbia
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agar 5% sheep blood (BioMérieux, Lyon, France)
plates and incubated at 22 °C. Biochemical characterization of isolated bacteria was performed
using conventional tests and the API 20 E system
(BioMérieux) incubated at 25 °C. Antibiotic susceptibility was assayed by the disc diffusion method
on Müeller–Hinton agar.
Results
Bacterial characterization
Pure bacterial isolates were obtained after 12 h
incubation with round and grey-coloured colonies.
The isolated bacteria were motile small, Gramnegative rods and negative with the cytochromeoxidase reaction. They exhibited phenotypic
characteristics typical of E. tarda. The results of
morphological and biochemical tests are given in
Table 1. The numerical profile obtained from the
API20E system was 4344000. Antibiotic susceptibility tests indicated that the E. tarda isolates were
sensitive to florfenicol, oxytetracycline and trimethoprim-sulphametoxazole (Table 2).
Table 1 Biochemical characteristics of Edwardsiella tarda isolated from turbot (+, positive reaction; ), negative reaction).
Incubation temperature: 25 °C
Gram stain
Cell morphology
Cytochrome-oxidase
Catalase
Motility
Citrate utilization
H2S from TSI
API 20-E tests
b-galactosidase
Arginine dihydrolase
Lysine decarboxylase
Ornithine decarboxylase
Citrate utilization
H2S production
Urease hydrolysis
Deaminase
Indole production
Acetoin production
Gelatinase
Fermentation of
Glucose
Mannitol
Inositol
Sorbitol
Rhamnose
Sucrose
Melibiose
Amygdalin
Arabinose
)
Small rod
)
+
+
)
+
)
)
+
+
+(?)
)
)
)
+
+
)
+
)
)
)
)
)
)
)
)
F Padrós et al. Pathology of edwardsiellosis in turbot
Journal of Fish Diseases 2006, 29, 87–94
Table 2 Drug sensitivity of Edwardsiella tarda isolated from
turbot
Amoxycillin (25 lg)
Erythromycin (15 lg)
Florfenicol (30 lg)
Flumequine (30 lg)
Oxolinic acid (2 lg)
Oxytetracycline (30 lg)
Trimethoprim-sulphametoxazole (1.25 + 23.75 lg)
I
R
S
I
I
S
S
S, sensitive; I, intermediate; R, resistant.
Gross pathology and organ imprints
Affected fish presented evident tumefaction around
the eyes (Fig. 1) and also at the bases of the dorsal
and anal fins. When these tumefacted areas were
incised, an accumulation of a purulent fluid was
seen. In some fish, haemorrhages were also observed
in the musculature, mainly in the head region. The
abdomen was distended because of the presence of
ascitic fluid, with the presence of fibrin. Haemorrhages in the liver and generalized congestion of the
intestine, spleen and kidney were also observed. The
kidney and spleen were clearly enlarged, especially
the kidney, where abscess-like lesions filled with a
purulent fluid were evident. Gram-stained imprints
of the liver, spleen and kidney showed significant
numbers of small Gram-negative rods both inside
the macrophages and extracellularly.
Histopathology
Kidney
Figure 1 Macroscopic lesions associated with Edwardsiella tarda
in turbot. Note the evident oedema around the eyes.
Figure 2 Large abscesses in turbot trunk
kidney. Note the presence of a core loaded
with necrotic material (arrowheads) and an
inflammatory zone (arrows) surrounding the
abscess (H&E, bar ¼ 215 lm).
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The main change observed was the presence of
abscesses. These were situated in the haematopoietic
tissue of the head and trunk kidney and presented
different sizes and stages of organization. Small
abscesses were observed as aggregations of macrophages with a large number of bacteria within their
cytoplasm. Larger abscesses (Fig. 2) had a core of
necrotic material, mainly formed by a large number
of necrotic cells and some bacterial cells. Around
these abscesses, a significant inflammatory response
was observed. This was characterized by the presence of large numbers of macrophages, mostly
packed with many bacterial cells, as well as other
inflammatory cells (mainly neutrophils), and fibrin
layers. Haemorrhage around the abscesses was also a
F Padrós et al. Pathology of edwardsiellosis in turbot
Journal of Fish Diseases 2006, 29, 87–94
common finding. Although small abscesses were
observed in all the affected turbot examined, large
abscesses were not always seen. No granulomatous
reaction was noticed in any of the samples. The rest
of the haemopoietic tissue was also changed. Single
or very small groups of macrophages containing a
large number of bacteria (Fig. 3) were seen. These
cells were similar to those observed in the small
abscesses and in the areas surrounding the larger
abscesses. Groups of necrotic haemopoietic cells
were disseminated throughout the haemopoietic
tissue. Renal sinusoids were not obviously affected
and only few bacterial cells were observed in the
blood vessels or free in the interstitial spaces. The
excretory structures (renal corpuscles and tubules)
seemed to be slightly affected and only those located
in the vicinity of the abscesses were clearly damaged.
Ultrastructural observations (Fig. 4) showed that
some bacteria were engulfed in intracytoplasmic
vacuoles. Most of the macrophages displayed clear
degenerative features in the nucleus and mitochondrial structures (Fig. 5). Most of the bacteria
showed no apparent alterations and, in some cases,
were dividing.
Spleen
Large numbers of macrophages loaded with bacteria, similar to those observed in the kidney, were
dispersed between splenic sinusoids. Only a few
Figure 3 Head kidney. Detached and small
groups of macrophages with a large number
of bacterial cells in the cytoplasm (arrows)
are seen (H&E, bar ¼ 21 lm).
Figure 4 Kidney (TEM): a macrophage filled with a large number of bacteria is seen.
Notice also that most of the bacterial cells do
not show apparent changes and in some
cases appear to be dividing (arrow)
(bar ¼ 2 lm).
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Journal of Fish Diseases 2006, 29, 87–94
M
?
M
?
Figure 5 Kidney (TEM): macrophages filled
with bacterial cells showing clear degenerative changes in mitochondria (arrows) and
endoplasmic reticulum (arrowheads) and the
presence of a large number of myelin figures
(M) (bar ¼ 2 lm).
M
Figure 6 Liver: macrophage (MC) surrounded by hepatocytes (H) and adjacent to
a lymphocyte (L). Notice the absence of
clear degenerative changes as shown in
Fig. 5 and the presence of only a small
number of bacterial cells within the
cytoplasm. Note that some of the bacterial
cells are within intracytoplasmic vacuoles
(arrowheads) (bar ¼ 5 lm).
bacteria were found in the extracellular spaces or in
the blood vessels. Ellipsoids appeared enlarged and
reticular cells also contained bacteria within their
cytoplasm, although to a lesser extent. Surprisingly,
only very few bacterial cells were associated with the
macrophage centres which did not display major
alterations. Ultrastructural observations of the
spleen did not differ from those described in the
kidney.
cells (Fig. 6). These macrophages were usually
embedded in a fibrin matrix and did not often
display the degenerative changes observed in the
kidney and spleen. No microorganisms were
observed in either the extracellular spaces or the
vascular endothelia of the hepatic sinusoids. However, in some cases, macrophages (potentially
monocytes) loaded with bacterial cells were
observed in the lumen of sinusoids. Hepatocytes
were not obviously affected.
Liver
The liver was not extensively damaged and few
lesions were observed. These consisted of small
groups of macrophages containing few bacterial
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Discussion
The macroscopic lesions described in the present
report are similar to those previously described for
Journal of Fish Diseases 2006, 29, 87–94
edwardsiellosis in turbot by Nougayrede et al.
(1994). Temperatures during the outbreak, rearing
density and mortalities were also similar in both
cases. Microbiological studies confirmed that in
both cases E. tarda was the bacterium responsible
for the outbreaks. Only the results of citrate
utilization (positive in our case, but only in the
API 20E system) differed from the data of Nougayrede et al. (1994), but the use of citrate may vary
between strains (Whitman 2004).
Most of the macroscopic lesions observed in
the present study cannot be considered pathognomonic of edwardsiellosis. Dermal lesions are
frequent in turbot infected by A. salmonicida,
T. maritimum and L. anguillarum. Tumefaction
around the eyes is also a typical sign of infection
by S. parauberis and reddening around the mouth
and fins is also a common lesion observed in
vibriosis. Therefore, in order to improve the
accuracy of the diagnosis, additional histopathological study is indicated.
The histopathological lesions observed in our
work are similar in many ways to the lesions
described in other fish species affected by E. tarda.
Histopathological studies on infections by E. tarda
have been made in a number of different species
by Miyazaki & Egusa (1976a,b,c) and Miyazaki
(1980) described the infection in Japanese eel,
Anguilla japonica (Temminck & Schlegel), Miyazaki & Plumb (1985) in channel catfish, Ictalurus
punctatus (Rafinesque), and Blazer, Shotts &
Waltman (1985) in Danio devario (Hamilton).
Miyazaki & Kaige (1985) described the comparative histopathology of edwardsiellosis caused by
E. tarda and E. ictaluri in different fish species.
These authors described the inflammatory
response of Japanese eel, A. japonica and Japanese
flounder, P. olivaceus, to E. tarda and that of
channel catfish, I. punctatus to E. ictaluri as
suppurative. In contrast, they described the
response of red sea bream, Pagrus major (Temminck & Schlegel), and tilapia, Tilapia nilotica
(L.), as granulomatous. Our results clearly show
that the lesions associated with the infection of
turbot by E. tarda are similar to those described
as ÔsuppurativeÕ lesions by Miyazaki & Kaige
(1985). These authors use the term ÔsuppurativeÕ
mainly to refer to the presence of abscesses.
However, the formation of true abscesses in fish is
debatable, as the formation of pus is not considered a feature of teleost inflammation (Ferguson
1989). The presence in the kidney of large
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numbers of aggregates of macrophages, neutrophils and fibrinous exudates surrounding a central
mass of necrotic and liquefacted material is
termed as purulent or apostematous inflammation
in mammals. Therefore, in sensu lato, these lesions
in fish can also be described as abscesses. For
histopathological diagnosis, the presence of abscesses in the kidney and spleen is an important
feature. Vibriosis in turbot, as in other fish
species, is usually characterized by a septicaemic
distribution of bacterial cells in the heart and
vascular components of the spleen and haematopoietic kidney, as well as in blood capillaries of
other well-vascularized organs such as the gills,
liver and the skeletal musculature. Vibrionaceae
are usually observed as detached cells, free within
the blood vessels and forming aggregates or
colonies. Furunculosis can also be diagnosed by
the presence of large colonies of bacteria, mainly
in the kidney, spleen, gills and particularly in the
heart. Tenacibaculum maritimum infections are
usually not characterized by the expression of
significant inflammatory reactions. Serratia liquefaciens infections are characterized by the presence
of numerous necrotic foci in the kidney, spleen or
liver, but not by apostematous lesions. The
microscopic and ultrastructural observations described here suggest that macrophages may play an
important role in the pathogenesis of the disease.
Bacterial cells were mainly found in association
with macrophages. The apparent absence of
bacteria in blood vessels and extracellular spaces
may either be explained by the clearance activity
of macrophages, or bacterial taxis towards these
cells. However, the number of bacteria observed
within the cytoplasm of kidney and spleen
macrophages was very high and seemed to exceed
macrophage capacity to destroy them.
Edwardsiellosis (Miyazaki & Kaige 1985), bacterial kidney disease (Bruno 1986) and chronic
forms of pasteurellosis (Quaglio, Fucilli, Bertoja &
Giorgetti 1991; Noya, Magariños, Toranzo &
Lamas 1995) are examples of diseases where
macrophages play a significant role in defence
reactions. However, these responses may be
expressed in different ways. Granulomatous reactions are usually related to chronic infections, where
the pathogens can be confined and isolated from
healthy tissues by an effective and coordinated
proliferation of macrophagic cells (macrophages,
syncytial cells, epithelioid cells) and connective
tissue (fibroblasts). Apostematous lesions are related
Journal of Fish Diseases 2006, 29, 87–94
to subacute infection, where the isolation of the
pathogens is not complete. The presence of dividing
E. tarda inside phagocytic cells was seen in the
current study and it was also demonstrated in
experimental edwardsiellosis in flounder (Mamnur,
Nakai, Muroga & Miyazaki 1997), which supports
the idea of an incomplete isolation of E. tarda, as
well as a potential dissemination of the pathogen
through blood macrophages.
Acknowledgements
The authors thank Belen Fouz (Departamento de
Microbiologı́a y Ecologı́a, Facultad de Biologı́a,
Universidad de Valencia) and Mireya Alvarez
(Skretting) for helping in the bacterial identification
studies.
References
Alsina M. & Blanch A.R. (1993) First isolation of Flexibacter
maritimus from cultivated turbot (Scophthalmus maximus).
Bulletin of the European Association of Fish Pathologists 13,
157–160.
Austin B., Stobie M., Robertson P.A.W., Glass H.G., Stark J.R.
& Mudarris M. (1993) Vibrio alginolyticus: the cause of gill
disease leading to progressive low-level mortalities among
juvenile turbot, Scophthalmus maximus (L.), in a Scottish
aquarium. Journal of Fish Diseases 16, 277–280.
Blazer V.S., Shotts E.B. & Waltman W.D. (1985) Pathology
associated with Edwardsiella ictaluri in catfish, Ictalurus
punctatus Rafinesque and Danio devario (Hamilton-Buchanan). Journal of Fish Biology 27, 167–175.
Bruno D.W. (1986) Histopathology of bacterial kidney disease
in laboratory infected rainbow trout, Salmo gairdneri Richardson, and Atlantic salmon, Salmo salar L., with reference
to naturally infected fish. Journal of Fish Diseases 9,
523–537.
Devesa S., Toranzo A.E. & Barja J.L. (1985) First report of
vibriosis in turbot (Scophthalmus maximus) cultured in
Northwestern Spain. In: Fish and Shellfish Pathology (ed. by
A.E. Ellis), pp. 131–140. Academic Press, London.
Doménech A., Fernández-Garayzabal J.F., Pascual C., Garcı́a
J.A., Cutuli M.T., Moreno M.A., Collins M.D. & Domı́nguez L. (1996) Streptococcosis in cultured turbot, Scophthalmus maximus (L.), associated with Streptococcus parauberis
(L). Journal of Fish Diseases 19, 33–38.
Ferguson H.W. (1989) Systematic Pathology of Fish. Iowa State
University Press, Ames, IA.
Fouz B., Larsen J.L. & Toranzo A.E. (1991) Vibrio damsela as a
pathogenic agent causing mortalities in cultured turbot
(Scophthalmus maximus). Bulletin of the European Association of
Fish Pathologists 11, 80–81.
Fouz B., Larsen J.L., Nielsen B., Barja J.L. & Toranzo A.E.
(1992) Characterization of Vibrio damsela strains isolated from
Ó 2006
Blackwell Publishing Ltd
93
F Padrós et al. Pathology of edwardsiellosis in turbot
turbot Scophthalmus maximus in Spain. Diseases of Aquatic
Organisms 12, 155–166.
Horne M.T., Richards R.H., Roberts R.J. & Smith P.C. (1977)
Peracute vibriosis in juvenile turbot Scophthalmus maximus.
Journal of Fish Biology 11, 355–361.
Kusuda R. & Kawai K. (1998) Bacterial diseases of cultured
marine fish in Japan. Fish Pathology 33, 221–234.
Mamnur R.M., Nakai T., Muroga K. & Miyazaki T. (1997)
Pathogenesis of experimental edwardsiellosis in Japanese
flounder Paralichthys olivaceus. Fisheries Science 63,
384–387.
Miyazaki T. (1980) Histopathological study on bacterial infections of fishes. Bulletin of the Faculty of Fisheries, Mie University
7, 63–149.
Miyazaki T. & Egusa S. (1976a) Histopathological studies on
Edwardsiella tarda infection of the Japanese eel – I. Natural
infection-suppurative interstitial nephritis form. Fish Pathology
11, 33–43.
Miyazaki T. & Egusa S. (1976b) Histopathological studies on
Edwardsiella tarda infection of the Japanese eel – II. Natural
infection-suppurative hepatitis form. Fish Pathology 11,
67–76.
Miyazaki T. & Egusa S. (1976c) Histopathological studies on
Edwardsiella tarda infection of the Japanese eel – III. Natural
infection-elvers. Fish Pathology 11, 127–132.
Miyazaki T. & Kaige N. (1985) Comparative histopathology of
edwardsiellosis in fishes. Fish Pathology 20, 219–227.
Miyazaki T. & Plumb J.A. (1985) Histopathology of
Edwardsiella ictaluri in channel catfish, Ictalurus punctatus
(Rafinesque). Journal of Fish Diseases 8, 389–392.
Nougayrede P., Sochon E. & Vuillaume A. (1990) Isolation of
Aeromonas subspecies salmonicida in farmed turbot (Psetta
maxima) in France. Bulletin of the European Association of Fish
Pathologists 10, 139–140.
Nougayrede Ph., Vuillaume A., Vigneulle M., Faivre B., Luengo
S. & Delprat J. (1994) First isolation of Edwardsiella tarda
from diseased turbot (Scophthalmus maximus) reared in a sea
farm in the Bay of Biscay. Bulletin of the European Association
of Fish Pathologists 14, 128–129.
Noya M., Magariños B., Toranzo A.E. & Lamas J. (1995)
Sequential pathology of experimental pasteurellosis in gilthead
seabream Sparus aurata. A light and electron-microscopic
study. Diseases of Aquatic Organisms 21, 177–186.
Pazos F., Santos Y., Núñez S. & Toranzo A.E. (1993) Increasing
occurrence of Flexibacter maritimus in the marine aquaculture
of Spain. FHS/AFS Newsletters 21, 1–2.
Pedersen K., Kofod H., Dalsgaard I. & Larsen J.L. (1994) Isolation of oxidase-negative Aeromonas salmonicida from diseased
turbot Scophthalmus maximus. Diseases of Aquatic Organisms
18, 149–154.
Plumb J.A. (1993) Edwardsiella septicaemia. In: Bacterial Diseases of Fish (ed. by V. Inglis, R.J. Roberts & N.R. Bromage),
pp. 61–79. Blackwell Scientific Publications, Oxford.
Quaglio F., Fucilli F., Bertoja G.L. & Giorgetti G. (1991) Fish
pasteurellosis: a review. Rivista Italiana di Acquacoltura 26,
179–197.
Journal of Fish Diseases 2006, 29, 87–94
Toranzo A.E., Devesa S., Heinen P., Riaza A., Núñez S. & Barja
J.L. (1994) Streptococcosis in cultured turbot caused by an
Enterococcus-like bacterium. Bulletin of the European Association of Fish Pathologists 14, 21–23.
Vigneulle M. & Baudin Laurencin F. (1995) Serratia liquefaciens:
a case report in turbot (Scophthalmus maximus) cultured in
floating cages in France. Aquaculture 132, 121–124.
Ó 2006
Blackwell Publishing Ltd
94
F Padrós et al. Pathology of edwardsiellosis in turbot
Whitman K.A. (2004) Finfish and Shellfish Bacteriology Manual.
Iowa State Press, Ames, IA.
Received: 22 February 2005
Revision received: 8 August 2005
Accepted: 17 August 2005