335
Although catastrophic losses of catfi sh have not been recorded, the disease has a
severe economic effect on infected sites. When infected fi sh enter processing plants,
the noxious odours effectively stop production by necessitating disinfection and
deodorisation. Thus, heavy fi nancial losses to the processors may result from the
presence of only a small number of infected animals (Meyer and Bullock 1973 ).
Examination of naturally diseased tilapia has indicated a range of symptoms
including loss of pigmentation, the presence of a swollen abdomen fi lled with ascitic
fl uid, protruded haemorrhaged anus and opaqueness to the eyes. Internally, small
white nodules may be observed in the gills, kidney, liver and spleen, and occasionally the intestine. These nodules are packed with bacteria (Kubota et al. 1981 ).
Diseased turbot in Spain revealed the presence of eye tumefaction, haemorrhaging, infl ammation (kidney, liver and spleen) and ascites (Padrós et al. 2006 ).
Subsequently, the organism became associated with disease in farmed Senegalese
sole in Spain (Castro et al. 2012 ).
In China, turbot exhibited one of two set of external signs – blackening of the
dorsal surface on the posterior part of the body; and red cutaneous foci on the ventral surface. The kidneys were enlarged (Qin et al. 2014 ). Giant mottled eel ( Anguilla
marmorata ) developed extreme ulceration with haemorrhaging, swelling of the kidney and liver, and liquefactive necrosis in the brain leading to high mortalities (Mo
et al. 2015 ).
Isolation
Isolation of Edw. tarda from diseased fi sh is a straightforward procedure involving
the use of commonly available media, such as TSA (Meyer and Bullock 1973 ;
Alcaide et al. 2006 ) or BHIA (Amandi et al. 1982 ). On such media, small round
(0.5 mm in diameter) raised, transparent colonies develop in 48 h at 24–26 °C
(Meyer and Bullock 1973 ). The use of thioglycollate broth followed by subculturing on BHIA has also been used successfully (Appendix in Chap. 12 ; Amandi et al.
1982 ). Indeed, this two-step enrichment procedure has proved to be more sensitive
than BHIA used alone. In one experiment, this two-step procedure enabled the
recovery of Edw. tarda from 19 % of a group of chinook salmon, compared to only
2 % recovery on BHIA used alone (Amandi et al. 1982 ). A selective and differential
medium, ET, which was originally published by Lindquist ( 1991 ), has enabled the
recovery of Edw. tarda from mixed cultures following incubation at 25 °C for
24–48 h when transparent colonies with black centres were indicative of the pathogen (Appendix in Chap. 12 ; Castro et al. 2011 ).
Edwardsiella tarda
Although catastrophic losses of catfi sh have not been recorded, the disease has a
severe economic effect on infected sites. When infected fi sh enter processing plants,
the noxious odours effectively stop production by necessitating disinfection and
deodorisation. Thus, heavy fi nancial losses to the processors may result from the
presence of only a small number of infected animals (Meyer and Bullock 1973 ).
Examination of naturally diseased tilapia has indicated a range of symptoms
including loss of pigmentation, the presence of a swollen abdomen fi lled with ascitic
fl uid, protruded haemorrhaged anus and opaqueness to the eyes. Internally, small
white nodules may be observed in the gills, kidney, liver and spleen, and occasionally the intestine. These nodules are packed with bacteria (Kubota et al. 1981 ).
Diseased turbot in Spain revealed the presence of eye tumefaction, haemorrhaging, infl ammation (kidney, liver and spleen) and ascites (Padrós et al. 2006 ).
Subsequently, the organism became associated with disease in farmed Senegalese
sole in Spain (Castro et al. 2012 ).
In China, turbot exhibited one of two set of external signs – blackening of the
dorsal surface on the posterior part of the body; and red cutaneous foci on the ventral surface. The kidneys were enlarged (Qin et al. 2014 ). Giant mottled eel ( Anguilla
marmorata ) developed extreme ulceration with haemorrhaging, swelling of the kidney and liver, and liquefactive necrosis in the brain leading to high mortalities (Mo
et al. 2015 ).
Isolation
Isolation of Edw. tarda from diseased fi sh is a straightforward procedure involving
the use of commonly available media, such as TSA (Meyer and Bullock 1973 ;
Alcaide et al. 2006 ) or BHIA (Amandi et al. 1982 ). On such media, small round
(0.5 mm in diameter) raised, transparent colonies develop in 48 h at 24–26 °C
(Meyer and Bullock 1973 ). The use of thioglycollate broth followed by subculturing on BHIA has also been used successfully (Appendix in Chap. 12 ; Amandi et al.
1982 ). Indeed, this two-step enrichment procedure has proved to be more sensitive
than BHIA used alone. In one experiment, this two-step procedure enabled the
recovery of Edw. tarda from 19 % of a group of chinook salmon, compared to only
2 % recovery on BHIA used alone (Amandi et al. 1982 ). A selective and differential
medium, ET, which was originally published by Lindquist ( 1991 ), has enabled the
recovery of Edw. tarda from mixed cultures following incubation at 25 °C for
24–48 h when transparent colonies with black centres were indicative of the pathogen (Appendix in Chap. 12 ; Castro et al. 2011 ).
Edwardsiella tarda