217
The sub-acute or chronic form of furunculosis, which is more common in older
fi sh, is characterised by lethargy, slight exophthalmia, blood-shot fi ns, bloody discharge from the nares and vent, and multiple haemorrhages in the muscle and other
tissues. Internally, haemorrhaging in the liver, swelling of the spleen, and kidney
necrosis may occur (Snieszko 1958a ; McCarthy and Roberts 1980 ). This form of
the disease usually causes low rates of mortality, and fi sh may survive, although
survivors have scar tissue in the vicinity of the furuncles (McCarthy 1975a ). Oddly
enough, the chronic form of the disease is not the most frequently occurring, nor is
the presence of furuncles the most typical symptom of the disease (Snieszko 1958a ).
The acute form of furunculosis, which is most common particularly in growing
fi sh and adults, is manifested by a general septicaemia accompanied by melanosis,
inappetance, lethargy, and small haemorrhages at the base of the fi ns. This form of
the disease is of short duration, insofar as the fi sh usually die in 2–3 days, and
causes high mortalities. The bacteria occur in the blood, disseminated throughout
the tissues, and in the lesions. Internally, haemorrhaging occurs over the abdominal
walls, viscera and heart. The spleen may appear enlarged. The acute disease is of
sudden onset, with few, if any, external signs (McCarthy 1975a ).
McCarthy and Roberts ( 1980 ) discussed a third clinical form of furunculosis,
termed peracute furunculosis, which is confi ned to fi ngerling fi sh. The infected animals darken in colour, and may quickly die with only slight external symptoms,
such as mild exophthalmia. Haemorrhages may occur at the base of the pectoral fi n,
if the fi sh manage to survive for long enough periods. Losses in farmed stock may
be extremely high (Davis 1946 ).
Yet another form of furunculosis was discussed by Amlacher ( 1961 ), i.e. intestinal furunculosis. The symptoms were described as infl ammation of the intestine,
and anal inversion. This description is similar to a report by Herman ( 1968 ) of
chronic furunculosis, i.e. low, relatively constant rate of mortality with intestinal
infl ammation and variable haemorrhages.
In addition to furunculosis, Aer. salmonicida has been implicated in other conditions often ulcerative, in freshwater and marine species, including wrasse (Laidler
et al. 1999 ), Arctic charr ( Salvelinus alpinus ) and grayling ( Thymallus thymallus )
(Pylkkö et al. 2005 ). Atypical Aer. salmonicida has recently been associated with
ulcerations in Atlantic salmon in Chile (Godoy et al. 2010 ). The best known of the
ulcerative conditions is undoubtedly carp erythrodermatitis (CE; Fig. 5.3 ). Fijan
( 1972 ), who is credited with the name of the disease, demonstrated that CE was
caused by a transmissible, antibiotic-sensitive organism, which manifested itself as
predominantly a skin infection. Bootsma et al. ( 1977 ) isolated a small, Gramnegative, rod-shaped organism from skin lesions in mirror carp in Yugoslavia. This
organism was subsequently identifi ed as an “atypical” strain of Aer. salmonicida .
CE was described as a sub-acute to chronic contagious skin disease, which varied in
its morbidity and mortality (Bootsma et al. 1977 ). It appears that the infection often
starts at the site of injury to the epidermis. A haemorrhagic infl ammatory process
then develops between the epidermis and dermis. This red infl ammatory zone gradually extends as the infection spreads. The breakdown of tissue leads to the formation of a central ulcer, which may occur in any location on the body surface, although
Aeromonas salmonicida
The sub-acute or chronic form of furunculosis, which is more common in older
fi sh, is characterised by lethargy, slight exophthalmia, blood-shot fi ns, bloody discharge from the nares and vent, and multiple haemorrhages in the muscle and other
tissues. Internally, haemorrhaging in the liver, swelling of the spleen, and kidney
necrosis may occur (Snieszko 1958a ; McCarthy and Roberts 1980 ). This form of
the disease usually causes low rates of mortality, and fi sh may survive, although
survivors have scar tissue in the vicinity of the furuncles (McCarthy 1975a ). Oddly
enough, the chronic form of the disease is not the most frequently occurring, nor is
the presence of furuncles the most typical symptom of the disease (Snieszko 1958a ).
The acute form of furunculosis, which is most common particularly in growing
fi sh and adults, is manifested by a general septicaemia accompanied by melanosis,
inappetance, lethargy, and small haemorrhages at the base of the fi ns. This form of
the disease is of short duration, insofar as the fi sh usually die in 2–3 days, and
causes high mortalities. The bacteria occur in the blood, disseminated throughout
the tissues, and in the lesions. Internally, haemorrhaging occurs over the abdominal
walls, viscera and heart. The spleen may appear enlarged. The acute disease is of
sudden onset, with few, if any, external signs (McCarthy 1975a ).
McCarthy and Roberts ( 1980 ) discussed a third clinical form of furunculosis,
termed peracute furunculosis, which is confi ned to fi ngerling fi sh. The infected animals darken in colour, and may quickly die with only slight external symptoms,
such as mild exophthalmia. Haemorrhages may occur at the base of the pectoral fi n,
if the fi sh manage to survive for long enough periods. Losses in farmed stock may
be extremely high (Davis 1946 ).
Yet another form of furunculosis was discussed by Amlacher ( 1961 ), i.e. intestinal furunculosis. The symptoms were described as infl ammation of the intestine,
and anal inversion. This description is similar to a report by Herman ( 1968 ) of
chronic furunculosis, i.e. low, relatively constant rate of mortality with intestinal
infl ammation and variable haemorrhages.
In addition to furunculosis, Aer. salmonicida has been implicated in other conditions often ulcerative, in freshwater and marine species, including wrasse (Laidler
et al. 1999 ), Arctic charr ( Salvelinus alpinus ) and grayling ( Thymallus thymallus )
(Pylkkö et al. 2005 ). Atypical Aer. salmonicida has recently been associated with
ulcerations in Atlantic salmon in Chile (Godoy et al. 2010 ). The best known of the
ulcerative conditions is undoubtedly carp erythrodermatitis (CE; Fig. 5.3 ). Fijan
( 1972 ), who is credited with the name of the disease, demonstrated that CE was
caused by a transmissible, antibiotic-sensitive organism, which manifested itself as
predominantly a skin infection. Bootsma et al. ( 1977 ) isolated a small, Gramnegative, rod-shaped organism from skin lesions in mirror carp in Yugoslavia. This
organism was subsequently identifi ed as an “atypical” strain of Aer. salmonicida .
CE was described as a sub-acute to chronic contagious skin disease, which varied in
its morbidity and mortality (Bootsma et al. 1977 ). It appears that the infection often
starts at the site of injury to the epidermis. A haemorrhagic infl ammatory process
then develops between the epidermis and dermis. This red infl ammatory zone gradually extends as the infection spreads. The breakdown of tissue leads to the formation of a central ulcer, which may occur in any location on the body surface, although
Aeromonas salmonicida