520
Pathogenicity
Isolates caused disease and mortalities when injected i.p. into tongue sole, albeit at
high doses, i.e. 10
5 to 10
7 CFU/fi sh, with putative pathogenicity factors including
DNase, ß-haemolysin, lecithinase, lipase and protease (Zhang et al. 2011b ).
Vibrio alginolyticus
Characteristics of the Disease
The most extensive study of the role of V. alginolyticus as a fi sh pathogen concerned
the observations of mortalities in farmed sea bream (Sparus aurata) in Israel.
Mortalities were recorded after extensive handling of the fi sh (Colorni et al. 1981 ).
However, these workers were unable to reproduce the infection under laboratory
conditions, which casts some doubt on the importance of this organism in fi sh
pathology. Nevertheless, there is additional evidence linking this organism with a
pathogenic mode. From the description of Colorni et al. ( 1981 ) and Austin et al.
( 1993 ), the disease may be classifi ed as a typical bacterial septicaemia. Infected fi sh
were observed to become sluggish, the skin darkened, scales loosened and sloughed
off, and ulcers developed. The liver, capillaries in the intestinal wall, air bladder, and
peritoneum became congested. Simultaneously, the intestine and gall bladder
became distended with clear fl uid and bile, respectively. Anaemia and gill rot were
also reported. Austin et al. ( 1993 ) attributed the organism with gill disease leading
to progressive low-level mortalities in turbot, which were maintained at supraoptimal temperatures in a recirculating aquarium. Lee ( 1995 ) recovered one isolate,
which was identifi ed phenotypically, from diseased grouper (Epinephelus malabaricus), and attributed the organism with causing exophthalmia and corneal
opaqueness; signs that are reminiscent of the pathology caused by V. harveyi. Also,
occasional isolations have been made from ulcers (Akazaka 1968 ). Woo et al.
( 1995 ) and Ye et al. ( 1997 ) considered that V. alginolyticus was responsible for
heavy mortalities in silver sea bream (Sparus sarba) in Hong Kong. The organism
has also been associated with disease in gilt-head sea bream in Spain (Balebona
et al. 1998 ). Additionally, V. alginolyticus has been reported as a secondary invader
of sea mullet suffering with ‘red spot’ (Burke and Rodgers 1981 ). V. alginolyticus
has also been implicated with mortalities in cultured black sea bream fry (Kusuda
et al. 1986 ) and in cobia ( Rachycentron canadum ) in the latter case the disease signs
focused on sluggish swimming and bilateral exophthalmia leading to death
(Rameshkumar et al. 2014 ). Overall, there is some evidence that V. alginolyticus
may constitute an opportunistic invader of already damaged tissues, or a weak
pathogen of stressed fi sh.
10 Vibrios
Pathogenicity
Isolates caused disease and mortalities when injected i.p. into tongue sole, albeit at
high doses, i.e. 10
5 to 10
7 CFU/fi sh, with putative pathogenicity factors including
DNase, ß-haemolysin, lecithinase, lipase and protease (Zhang et al. 2011b ).
Vibrio alginolyticus
Characteristics of the Disease
The most extensive study of the role of V. alginolyticus as a fi sh pathogen concerned
the observations of mortalities in farmed sea bream (Sparus aurata) in Israel.
Mortalities were recorded after extensive handling of the fi sh (Colorni et al. 1981 ).
However, these workers were unable to reproduce the infection under laboratory
conditions, which casts some doubt on the importance of this organism in fi sh
pathology. Nevertheless, there is additional evidence linking this organism with a
pathogenic mode. From the description of Colorni et al. ( 1981 ) and Austin et al.
( 1993 ), the disease may be classifi ed as a typical bacterial septicaemia. Infected fi sh
were observed to become sluggish, the skin darkened, scales loosened and sloughed
off, and ulcers developed. The liver, capillaries in the intestinal wall, air bladder, and
peritoneum became congested. Simultaneously, the intestine and gall bladder
became distended with clear fl uid and bile, respectively. Anaemia and gill rot were
also reported. Austin et al. ( 1993 ) attributed the organism with gill disease leading
to progressive low-level mortalities in turbot, which were maintained at supraoptimal temperatures in a recirculating aquarium. Lee ( 1995 ) recovered one isolate,
which was identifi ed phenotypically, from diseased grouper (Epinephelus malabaricus), and attributed the organism with causing exophthalmia and corneal
opaqueness; signs that are reminiscent of the pathology caused by V. harveyi. Also,
occasional isolations have been made from ulcers (Akazaka 1968 ). Woo et al.
( 1995 ) and Ye et al. ( 1997 ) considered that V. alginolyticus was responsible for
heavy mortalities in silver sea bream (Sparus sarba) in Hong Kong. The organism
has also been associated with disease in gilt-head sea bream in Spain (Balebona
et al. 1998 ). Additionally, V. alginolyticus has been reported as a secondary invader
of sea mullet suffering with ‘red spot’ (Burke and Rodgers 1981 ). V. alginolyticus
has also been implicated with mortalities in cultured black sea bream fry (Kusuda
et al. 1986 ) and in cobia ( Rachycentron canadum ) in the latter case the disease signs
focused on sluggish swimming and bilateral exophthalmia leading to death
(Rameshkumar et al. 2014 ). Overall, there is some evidence that V. alginolyticus
may constitute an opportunistic invader of already damaged tissues, or a weak
pathogen of stressed fi sh.
10 Vibrios