Gram positive cocco-bacteria
(Micrococcaceae, Streptococcaceae)
causing systemic disease to intensively farmed marine fish in the
Mediterranean.
A brief review.
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Authored by Dr. PANOS VARVARIGOS |
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CONTENTS |
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Aspects of bacteriology
Family: Micrococcaceae
Staphylococci are gram-positive cocci (about 0.5 to 1.5μm in diameter) occurring singly, in pairs, in
tetrads, short chains of three or four cells, or most often in irregular
"grape-like" clusters. Their name is derived from their latter
frequent formation stemming from the Greek "staphylos"
meaning grape.
They are nonmotile, nonsporeforming and
usually catalase positive and unencapsulated.
Although most species are facultative anaerobes, growth is more rapid and
abundant under aerobic conditions. Most strains grow well on common noninhibitory media.
The cell wall contains peptidoglycan and teichoic acid.
The diamino acid present in the peptidoglycan
is L-lysine. Staphylococci are susceptible to lysis
by the endopeptidase lysostaphin.
They are generally resistant to lysis by the muramidase lysozyme.
Staphylococci are currently
included together with micrococci and planococci in the family Micrococcaceae
as a matter of convenience, since these genera are not closely related phylogenetically and should not be combined in one family.
All three genera represented in the family Micrococcaceae
are catalase-positive, gram-positive cocci with cell wall peptidoglycan
containing L-lysine as the diamino acid.
Micrococci are generally resistant to lysostaphin. Among others, staphylococci and micrococci may be differentiated on the basis of anaerobic
acid production from glucose, which is positive for most Staphylococcus
species and negative for most Micrococcus species.
Colonies of most
staphylococci, which have been isolated from fish on non-selective media, such
as tryptic soy agar (TSA), are circular, smooth and
raised with a butyrous consistency and a bright
white, sometimes glistening, or pale white colour. Their diameter may be 0,5-2mm subsequent to 36-48 hours of incubation at room
temperature of around 25°C. Such colonies may become sticky with age. Micrococci produce on TSA yellow colonies of similar shape.
Staphylococcus species are not possible to be
distinguished on the basis of colony morphology. Colonies conforming to the
description above should be Gram stained, sub-cultured and tested for genus and
species biochemical properties (e.g. by means of the API STAPH commercial
identification system). In human and veterinary medicine a few additional key
characteristics must be examined for the identification of the most clinically
significant species. Coagulase production is
significant among these, that is, the ability to clot blood plasma. A rapid
slide coagulase test may be performed. Most Staphylococcus
species isolated from fish are coagulase negative.
Family: Streptococcaceae
The genera Streptococcus,
Aerococcus, Leuconostoc, Pediococcus and Gemella
comprise the members of this family. Nevertheless, the taxonomic status of the
latter two genera is uncertain. They are gram-positive, cytochrome-negative
coccoidal bacteria that usually grow in chains of
various lengths and sometimes form tetrads. Under certain growth conditions
these bacteria are elongated and appear rod-like when Gram stained. Their name
is derived from their frequent chain formation stemming from the Greek "streptos" meaning twisted chain.
The most definitive
difference between the families Streptococcaceae
and Micrococcaceae is that catalase
is most often absent from the cultures of the former and present in the
cultures of the latter.
Streptococci and aerococci are mostly important in human and veterinary
medicine. Streptococci are oxidase negative and catalase negative. Some streptococcal species contain
specific polysaccharide antigens and are classified into distinct groups
(Lancefield groups) according to the presence of these group-specific antigens
(groups: A, B, C, D, E, F, G, H, K, L, M, N, O).
The group D streptococci
are normal inhabitants of the human gastrointestinal tract, but may spread to
cause wound infections and bacteremia. The medically
important group D streptococci are divided into the enterococcal
species (S. faecalis, S. faecium,
S. durans, S. avium) and the non-enterococcal
species. (S. bovis, S. equinus).
The group D streptococci produce colonies that resemble those of staphylococci.
Complementary to the above
grouping and a most useful characteristic for the identification of streptococci,
is their haemolytic action on red blood cells (RBC's). Four distinct types of
haemolytic action are described and characterise streptococcal colonies grown
on the surface of blood agar:
Alpha-haemolysis: An indistint
zone of partial destruction of rbc's
appears around the colonies, often with a greenish to brownish discoloration of
the medium.
Beta-haemolysis: A clear, colourless zone appears around the colonies,
where the rbc's have been
completely discoloured.
No-haemolysis: No apparent haemolytic activity or discolouration of rbc's is notable around the
colonies.
Wide-zone alpha-haemolysis: A small halo of intact or partially lysed rbc's
lies adjacent to the colonies, but a wider zone of complete haemolysis extends
farther out into the medium. (Macroscopically may be confused with
beta-haemolysis).
For the presumptive
identification of the major categories of streptococci and aerococci,
once isolated in pure culture, the catalase-negative,
gram positive coccus is tested for haemolysis. In
addition, the results of the tests that follow may be used:
Salt tolerance (6.5% NaCl) test: Visible growth within 24 hours after inoculation onto 6.5% NaCl agar indicates that the strain is salt tolerant, i.e.,
positive and it can be identified as an enterococcus.
Bile-esculin
(BE) hydrolysis test:
When an agar plate is incubated for 24-48 hours at 35-37°C subsequent to
inoculation by the BE medium, which has been inoculated in turn with 3
colonies, a positive test produces blackening of the medium. Otherwise the test
is negative. All group D streptococci (enterococci as
well as non-enterococci) are BE positive.
Susceptibility to SXT
test: Most group A
and B streptococci are resistant to SXT when cultures are incubated in a normal
atmosphere. (SXT disks containing 1.25 mg of trimethoprim
and 23.75 mg of sulfamethoxazole.)
Presumptive
identification of streptococci and aerococci
|
Category |
Cellular arrangement |
Haemolysis |
Group antigen |
SXT resistance |
BE test |
Salt tolerance |
|
Group A strept. |
chains |
beta |
A |
yes |
-- |
-- |
|
Group B strept. |
chains |
beta |
B |
yes |
-- |
+ |
|
"Groupable" beta-haemolytic
streptococci, not group A, B, or D |
chains |
beta |
Not A, B, or D |
no |
-- |
-- |
|
Group D, enterococci |
short chains, diplo |
alpha, beta, none |
D |
yes |
+ |
+ |
|
Group D, not enterococci |
short chains, diplo |
alpha, none |
D |
no |
+ |
-- |
|
Viridans streptococci |
chains |
alpha, none |
none |
no |
-- |
-- |
|
Pneumonococci |
diplo, short chains |
alpha |
none |
? |
-- |
-- |
|
Aerococci |
single cells, tetrads |
alpha, none |
none |
? |
variable |
+ |
Since the
first publication of fish streptococcicosis/streptococcosis in 1958, there has been confusion about the
number and nature of the bacterial species involved (Austin and Austin, 1999). Serology has indicated that the
most common fish pathogenic streptococci are representatives of enterococci. Generally, serological techniques have not
improved the taxonomic status of the strains isolated form fish world-wide.
Many characteristics are shared by the majority of fish pathogens and there is
variance in the overall descriptions reported by different groups of workers.
For example, traits of streptococci that have
supposedly taxonomic significance, such as the ability to attack blood, have
been reported to vary. Fish pathogenic strains of streptococci have been
described, at one time or another, as either alpha or beta haemolytic or as non
haemolytic (Austin and Austin, 1999).
Overall, the isolates
recovered from fish may be clustered in the following taxa
(Austin and Austin, 1999):
Enterococcus (Streptococcus) faecalis subsp. liquefaciens
Produces yellow colonies of 1-2mm in diameter on TSA (despite
the fact that streptococci normally produce white colonies on TSA). Gram
positive cocci, which do not produce catalase, H2S or indole
and are VP negative (Voges Proskauer
reaction).
Lactococcus garvieae
(=Enterococcus seriolicida)
Alpha
haemolytic, Gram positive cocci in short chains,
which do not produce catalase, H2S, indole or oxidase. The VP
reaction is positive. The isolates are salt tolerant and do not correspond to
any of the serologically defined Lancefield groups of streptococci.
Lactococcus piscium
Represents a group of fish pathogenic lactococci/Group
N streptococci. They comprise Gram positive, non-motile, short (ovoid) rods,
which do not produce catalase or H2S. They
grow at 5-30°C.
Streptococcus difficilis (=Str. agalactiae)
Causes
meningo-encephalitis in cultured fish. Fairly unreactive and non-haemolytic,
Gram positive cocci of varying diameters in small
chains, which do not produce catalase and are not
salt tolerant. The VP reaction is positive. Str. difficilis
is similar to other group B, type Ib
streptococci in terms of biochemistry.
Streptococcus iniae (=Str. shiloi)
This
streptococcus was first isolated from an Amazon fresh water dolphin, Inia geoffrensis
and was later described as a cause of mortality in fish. After incubation for
24h at 30°C, colonies on BHIA are 1mm in diameter and non-pigmented. They
comprise Gram positive cocci in pairs and chains (pleomorphism has been observed), which do not produce catalase and are not salt tolerant. The VP reaction is
negative and α-heamolysis
is produced on bovine blood.
Streptococcus milleri
This streptococcus has been obtained from kidney samples of ulcerated koi carp. They comprise Gram positive cocci
in chains, which are catalase and oxidase
negative and are not salt tolerant. Weak β-heamolysis is produced on horse blood.
Streptococcus parauberis (=Str. uberis genotype II)
This
streptococcus has been isolated from diseased farmed turbot in Spain. After
incubation for 24h, whitish colonies of 1.5-2mm in diameter are produced, which
are slightly α-haemolytic. They comprise
non-motile Gram positive short rods/cocco-bacilli in
pairs or short chains, which are catalase negative
and are not salt tolerant.
Vagococcus salmoninarum
It has been isolated from diseased adult rainbow trout in Oregon, USA.
Cultures comprise Gram positive short oval rods, which are catalase
negative, H2S positive and are α-haemolytic. The VP
reaction is negative.
Epizootiology (Fish
susceptibility and transmission)
Streptococcosis
Reported epizootics of
streptococcus septicemia of fish worldwide involve
either group B streptococci or group D streptococci/enterococci.
The disease caused by bacteria of the genus Streptococcus and the genus Enterococcus is termed streptococcosis
or streptococcicosis and was first described among
rainbow trout in Japan in 1958. Since then the disease has gained importance
affecting a multitude of economically important farmed fish species.
Streptococcus sp. are
causing infections in rainbow trout (Onchorynchus mykiss) (Munday et al.,
1993). Lactococcus garvieae
(=Enterococcus seriolicida)
is infecting yellowtail (Seriola quinqueradiata) in Japan with serious economic
implications (Kusuda et al., 1991) and Streptococcus
iniae causes losses particularly in cultured ayu (Plecoglossus altivelis) also in Japan (Pier and Madin,
1976). Japanese eels, tilapia and coho salmon are
also prone to infection. Streptococcosis has spread
among rainbow trout farms in Australia, Israel, Italy and South Africa, but
also in catfish, silver trout, sea trout, stingray, striped bass and striped
mullet in the USA as well as Atlantic salmon farmed in Chile.
Infections caused by Lactococcus garvieae
(Lactococcosis) to salmonid
fish in Europe are becoming increasingly severe, particularly during the summer
months and in those European countries that experience warm weather. Lactococcosis occurs in both fresh and seawater. The
disease occurs also in Northern European countries, such as the UK and Norway.
There is evidence that
potentially pathogenic streptococci are found throughout the year in the
aquatic environment, that is, in the water, sediment and in the vicinity of
fish net pens. Their abundance in seawater increases during the warmer seasons
of the year. However, since the taxonomic status of fish pathogenic
streptococci is unclear, it cannot be proved that the strains isolated from the
farming environment are those causing fish disease; nonetheless, their presence
is an indicator of a non-sanitary environment.
Besides the potential role
of environmental contamination to fish health, it has been found that fish
pathogenic streptococci may be present in fresh and frozen fish used for
yellowtail diets. Hence, contaminated diets or raw materials may introduce the
pathogens to fish populations and the environment. Food-borne infections may be
the most important source for the spread of streptococcosis
among cultured fish.
Further, it has been proved
experimentally, that fish to fish transmission of the disease can be
facilitated through contact with infected fish. Streptococcosis
has been transmitted by means of cohabitation experiments (cohabiting
an infected fish with healthy specimens of the same species). Fish which
survive the disease may act as carriers. Wild fish may also carry the disease
asymptomatically.
Some host specificity to
streptococci exists, since different fish species show different sensitivity to
infection (intensity of symptoms, extent of internal organ damage, mortality)
by various bacterial strains.
Staphylococcosis
Staphylococcus epidermidis has been isolated from marine fish in Japan causing disease in red sea
bream (Chrysophrys major) and yellowtail (Seriola quinqueradiata)
showing exophthalmos and skin ulcers (Kusuda and Sugiyama, 1981). The bacteria were found to have
pronounced antigenic differences to human related strains; hence the infections
by Sta. epidermidis are considered to
originate from the aquatic environment. In fresh water fish Staphylococcus aureus has been reported from silver carp (Hypophthalmichthys nobilis)
in India causing corneal damage progressing to phthisis bulbi
(Shah and Tyagi, 1986).
In Greece, sporadic disease
with distinct pathogenicity is observed in fish
affecting most often young sea bream (Sparus auratus) and sea bass (Dicentrarchus
labrax). The disease is pronounced at the nursery
stage, or soon after transportation to the on-growing sites. It has been
investigated in a number of fish farms located in distinct regions and the
causative agents have been identified to be Gram positive cocci
of the genera Staphylococcus and Micrococcus. Although the
relatively younger fish seem mostly susceptible to the disease, larger fish,
even close to harvest size (>250g) have been found infected by
staphylococci.
In particular, during the
spring of 1997 severe outbreaks in both sea bream and sea bass occurred in
several fish farms scattered virtually throughout all fish farming regions of
Greece with daily mortality up to 2%.
Since 1997 several species
of staphylococci have been isolated either from sea bass or sea bream grown at
different farming locations in Greece. The most frequent were Staphylococcus
epidermidis, S. xylosus, S.
lentus, S. capitis, S. lugdunensis, S. hominis, S. warneri, S. cohnii, S. chromogenes and S. aureus.
Subsequent to Gram staining, identification of them was based on the API STAPH
(Biomerieux) system.
Mainly young fish of 0.5g
to 30g suffer. Due to the appearance of the external skin and fin lesions, staphylococcosis is often confused with myxobacteriosis.
Myxobacteria (Flexibacter sp.) commonly infect
the surface wounds of fish subsequent to handling (Noga,
1996, Pepin and Emery, 1993). However, the condition
does not recede after medicated bath treatments, which comprise a common
measure against myxobacteriosis, thus, alarming the
farmers.
Fish populations weakened
by staphylococcosis soon become infected by other
common warm water, Gram negative bacterial fish pathogens, such as Vibrio
spp. causing vibriosis and/or Photobacterium damsela subsp. piscicida causing pasteurellosis in both bass and bream (Post, 1987). Fish
resistance against parasitic infestations is compromised as well. In such
cases, symptoms and lesions are confused and antibiotic treatments may improve
health but do not offer a long-term cure. Reduction in mortality is short lived
and disease returns in a matter of few days. In sea bream fingerlings
infections by staphylococci often coincide with lymphocystis, hence the
diagnosis of staphylococcosis is obscured.
Although staphylococci may
be present in the environment throughout the year, the disease is exacerbated
by the rise in seawater temperatures. It appears in the spring and is spread
causing severe problems during the summer. Once established in a fish
population, staphylococcosis is contagious and
spreads easily among the fish of similar species or across the species that are
grown on the same farm, that is, from sea bass to sea bream and vice versa.
Other species on Greek farms that have been found infected include sharp snout
sea bream (Puntazzo puntazzo)
and dentex (Dentex dentex). Wild fish, mainly grey mullets (Mugil cephalus), that are
usually scavenging around the cages, are apparently infected and have been
frequently observed moribund showing similar symptoms.
As with the streptococcus
infections world-wide, there is evidence also in Greece which points strongly
towards the potential role that contaminated fish feeds may have regarding the
spread of staphylococcus infections among the cultured fish populations.
Preliminary microbiological studies of commercial fish feeds have shown high
levels of contamination of these products by potentially pathogenic
staphylococci.
Pathogenesis and diagnosis
The staphylococcal
infections, which have been diagnosed so far on cultured marine fish in Greece,
comprise infectious systemic diseases characterised by septicaemia. Similar
symptoms and lesions prevail on all fish species infected.
Despite the increasing
daily mortality and the number of dark coloured, lethargic, moribund fish
swimming erratically close to the surface and the corners of the net cage, the
infected population as a whole does not seem to loose its appetite and behaves
rather normally. Apart from the dark colouration and ataxia, the sick fish show
rather large external skin lesions covered by whitish mucus. By removing the
mucus surface necrosis in the form of shallow skin ulcers are uncovered. The
lips, mouth and lower jaws as well as the pectoral and the thoracic fins are
inflamed and necrotic (mouth rot, fin rot). Exophthalmia, progressing
inflammation and necrosis of the eye are not uncommon. In large sea bass, a
rather common symptom is the inflamed and protruding anus and the inflamed and
necrotic caudal fin.
|
Sea bass fry with deep ulcer uncovered when
the mucous layer is removed |
Sea bass fry showing skin inflammation
(reddening) |
|
Sea bream fry with inflamed and necrotic lips
and mouth tissues |
Sea bream with ulcerated skin |
|
Deep ulcers and fin rot in infected sharp
snout sea bream fry |
|
Necropsy reveals that the stomach
is invariably empty and the gut is distended to varying degrees containing a
watery fluid. Often the spleen is enlarged and most often the gall bladder is
distended and full of light yellow or dark green bile, especially in sparids (breams). The gills are usually anaemic with areas
of necrosis. The liver is usually pale and may show inflamed, darkened areas.
Congestion and haemorrhage of the brain is evident in small fry, mainly of sea
bass.
Apparently, the
staphylococci proliferate in the intestinal tract and cause enteritis with
diarrhoea, which may spread the cocci in the water
flushing and infecting other fish. Distension of the gall bladder may be a
result of cholocystitis and accumulation of
haemolysis products.
The staphylococci have been
isolated almost in pure culture by plating material taken from the anterior
kidney or the brain of the fish or from external necrotic lesions usually onto
TSA agar, Blood agar and Chapman agar. Small about 1mm, white, round and
regular colonies appear subsequent to incubation for 18 to 20 hours at 30-37oC.
Most of the species of
staphylococci that have been isolated from fish are coagulase
negative, namely, Staphylococcus epidermidis, S. xylosus, S. lentus, S. capitis, S. lugdunensis, S. hominis, S. warneri, S. cohnii, S. chromogenes. Only Staphylococcus
aureus has been found to be coagulase
positive.
The following table shows
the biochemical attributes of five Staphylococcus species, which are
often isolated.
Frequently isolated staphylococci from fish
with some of their biochemical attributes:
Staphylococcus spp.
|
Substrates |
S. aureus |
S. lentus |
S. xylosus |
S. epidermidis |
S. capitis |
|
Negative control |
- |
- |
- |
- |
- |
|
D-Glucose |
+ |
+ |
+ |
+ |
+ |
|
D-Fructose |
+ |
+ |
+ |
+ |
+ |
|
D-Mannose |
+ |
+ |
+ |
± |
+ |
|
Maltose |
+ |
+ |
+ |
+ |
- |
|
Lactose |
± |
+ |
+ |
+ |
- |
|
D-Trehalose |
+ |
+ |
+ |
- |
- |
|
D-Mannitol |
± |
+ |
+ |
- |
- |
|
Xylitol |
- |
+ |
- |
- |
- |
|
D-Melibiose |
- |
+ |
- |
- |
- |
|
Potassium nitrate |
+ |
+ |
+ |
± |
- |
|
β-naphthyl-acid phosphate |
+ |
- |
+ |
+ |
+ |
|
Sodium pyruvate |
± |
+ |
+ |
± |
+ |
|
Raffinose |
- |
+ |
+ |
- |
- |
|
Xylose |
- |
+ |
+ |
- |
- |
|
Sucrose |
+ |
+ |
+ |
+ |
- |
|
α-methyl-D-glucose |
- |
+ |
+ |
- |
- |
|
N-acetyl-glucosamine |
+ |
+ |
+ |
± |
- |
|
Arginine |
+ |
- |
- |
+ |
+ |
|
Urea |
± |
- |
+ |
+ |
- |
± variable reaction
It has been observed that
the progress of the staphylococcal infections in caged fish populations is rather
slow. Only few fish show ill-symptoms and die daily. Mortality persists.
Stress-related acute outbursts may occur, killing increased numbers of fish in
the course of a few days.
The disease spreads rapidly
among the fish population as well as to neighbouring cages holding the same or
other fish species. Daily mortality ranges between 0.1% and 2% and is related
to the stocking density in the net cage. Usually, there is good response
subsequent to the administration of the appropriate therapy. However, the
condition often persists and mortality gradually reappears. Field evidence
suggests that it is not easy to eradicate a staphylococcal infection when
established in a fish population. Apparently, it is not possible to eliminate
the pathogen from the fish or the environment. In addition, secondary
infections by Gram negative bacteria (Vibrio spp., Aeromonas spp.,
Photobacterium spp., Tenacibaculum spp.) may require treatments with
alternative antibiotics.
Diagnosis is based on the
clinical signs and necropsy and is confirmed by the isolation of the bacteria
on culture. The spread of a septicaemic ulcerative
disease across different fish species on a farm is close to pathognomonic.
Plating material from the internal organs (anterior kidney, spleen, liver) or
from the brain on TSA medium results in the growth of usually small, convex,
regular, white colonies after about 36 hours at room temperature (20-25°C).
Stained squash preparations from these organs may reveal the presence of Gram
positive cocci.
Prevention and treatment
There have been recent
vaccine developments against streptococcosis/lactococcosis caused in salmonid
fish by Lactococcus garvieae.
Reports on vaccine developments refer also to formulations containing antigens
against both Streptococcus iniae and Lactococcus garvieae,
suitable for administration by immersion, injection and even oral application.
However, these pathogens have not been confirmed to produce disease in the fish
species that are cultured in Greece. Hence, vaccination against disease caused
by Gram positive coccobacteria (staphyloccocci
or micrococci) is not an option yet in Greece.
Good husbandry ensuring
clean nets and overall farm hygiene as well as supply of good quality certified
fish feeds, which are fresh and have been properly stored
are the means for prevention.
When treatment is
considered necessary, potentiated sulfonamides, and oxytetracycline are usually effective. Occasionally,
erythromycin, ampicillin and amoxycillin
may be good alternatives. Sensitivity testing is always required prior to
deciding the preferred therapy.
Economic implications
With the exception of the Spring and Summer of year 1997, when staphylococci produced
infections throughout Greece, experience suggests that Gram positive coccobacteria (staphyloccocci or micrococci) are only occasionally present as secondary
pathogens, especially in weakened fish. Even in cases of young fry suffering
from staphylococcus or micrococcus septicaemia, mortality is rather low and the
condition improves soon after the administration of the proper therapy.
Overall, there is no hard evidence that such pathologies should be considered
crucial for the Greek aquaculture industry.
Regulations
Although there is no proof
that contamination of fish destined for human consumption by Gram positive
bacteria may pose any risk to consumer's health, these bacteria are indicators
of sub-standard product quality. This may be due to poor environmental
conditions or contaminated fish feeds used.
It would be advisable that
such incidences are investigated further.
There are currently no
regulations in place.
Reference list
(1)
Pier, G.B. and Madin, S.H. (1976)
Streptococcus iniae sp. nov.,
a beta-haemolytic streptococcus isolated from an Amazon freshwater dolphin, Inia geoffrensis. International
Journal of Systematic Bacteriology 26, 545-553.
(2)
Kusuda, R. and Sugiyama A. (1981)
Studies on the characters of Staphylococcus epidermidis
isolated from diseased fishes. Part 1. On the morphological, biological and biochemical properties.
Fish Pathol. 16,
15-24.
(3)
Manual of Clinical Microbiology (1985) Fourth
Edition. American Society for Microbiology, Washington, D.C., pp. 143-175.
(4)
Shah, K.L. and Tyagi, B.C. (1986)
An eye disease in silver carp, Hypophthalmichthys
molitrix, held in tropical ponds, associated with
the bacterium Staphylococcus aureus. Aquaculture
55, 1-4.
(5)
Post, G. (1987) Textbook of Fish Health.
Revised and Expanded Edition. T.F.H. Publications Inc.
(6)
Kusuda, R., Kawai, K., Salati,
F., Banner, C.R. and Fryer, J.I. (1991) Enterococcus seriolicida
sp. nov., a fish pathogen. International Journal
of Systematic Bacteriology 41, 406-409.
(7)
Munday, B.L., Jack, D.L., Schmidtke,
L. (1993) Pathogenicity
of the species Streptococcus causing disease in rainbow trout (Onchorynchus mykiss). Bulletin
of the European Association of Fish Pathologists 13(1), 25-27.
(8)
Pepin, J.P. and Emery, E. (1993)
Marine Cytophaga-like bacteria (CLB) isolated from
diseased reared sea bass (Dicentrarchus labrax) from French Mediterranean coast. Bulletin of
the European Association of Fish Pathologists 13(5), 165-167.
(9)
Noga, E.J. (1996) Fish
Disease: Diagnosis and Treatment. Mosby-Year Book Inc.
(10)
Gould, C. (2000) Lactococcosis
- a disease waiting i the wings. Fish
Farmer 23(3), 43.
(11)
News report. (2000) First
appearance of Lactococcus in Britain. Fish Farmer 23(6), 5.
(12)
Padilla, D., Real, F., Rodriguez, V., Gomez, S., and Acosta, F. (2001) Histological changes in Staphylococcus xylosus experimentally infected red porgy (Pagrus pagrus). Poster
presented at the 10th International Conference of the European Association of
Fish Pathologists "Diseases of Fish and Shellfish", held at Trinity
College, Dublin, Ireland. 9-14 September 2001.
Author:
Dr. Panos Varvarigos
Freelance
Veterinarian – Fish Pathologist, Athens, Greece.
AquaHealthTM
Laboratory.
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Every effort has been made to ensure that the
information is accurate until the date of last editing. It is based upon the
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The contents may be used as an educational guide and are definitely not meant
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