22
representatives of the family Bacteroidaceae. It is of course questionable whether or
not these bacteria will be recognised as fi sh pathogens in the future.
Clostridiaceae Representative
Clostridium botulinum
Characteristics of the Disease
The fi rst report of botulism as a disease of fi sh was from Denmark, stemming from
the work of Huss and Eskildsen ( 1974 ) when it was shown that the disease was
chronic, termed ‘bankruptcy disease’, and occurred in farmed trout, with the causal
agent recognised as Cl. botulinum type E. Later, the disease was found on one farm
of rainbow trout in Great Britain (Cann and Taylor 1982 , 1984 ) and was similarly
identifi ed among farmed coho salmon in the USA (Eklund et al. 1982 ), and subsequently associated with channel catfi sh in the USA (Chatla et al. 2012 ).
Characteristic disease symptoms were very vague, but fi sh have been observed to
exhibit abnormal sluggish, erratic swimming, appeared to be listless, and alternately fl oated and sank, before showing temporary rejuvenation. This pattern was
repeated until death eventually ensued (Cann and Taylor 1982 ; Khoo et al. 2011 ;
Beecham et al. 2014 ). Internally, there may be ascites, the brain, spleen and liver
may be congested, vascular dilation, oedema (fl uid retention) in the kidneys and
gastro-intestinal tract, and the blood supply interrupted to the intestines which
appeared to be blanched (Khoo et al. 2011 ). When the swimming speed is adversely
affected, the fi sh are likely to become more prone to predation (Beecham et al.
2014 ).
Isolation/Diagnosis of the Pathogen
Isolation is achieved by use of straightforward anaerobic techniques. Samples of
intestinal contents, which probably support a resident anaerobic microfl ora, and
internal organs should be homogenised in 1 % (w/v) peptone phosphate buffer at
pH 7.0, and diluted fi ve-fold. These diluted samples should be inoculated into
100 ml or 200 ml aliquots of Robertson’s meat broth (see Appendix in Chap. 12 ),
with subsequent anaerobic incubation at 30 °C for up to 6 days. Thereupon, the
presence of Cl. botulinum and its toxicity may be assessed (Cann et al. 1965a , b ;
Cann and Taylor 1982 ). In addition, sterile culture fi ltrates may be injected into
mice and/or fi sh to assess the presence of toxic factors (Cann and Taylor 1982 ).
However, the recovery of Cl. botulinum from intestinal samples should not be used
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)
representatives of the family Bacteroidaceae. It is of course questionable whether or
not these bacteria will be recognised as fi sh pathogens in the future.
Clostridiaceae Representative
Clostridium botulinum
Characteristics of the Disease
The fi rst report of botulism as a disease of fi sh was from Denmark, stemming from
the work of Huss and Eskildsen ( 1974 ) when it was shown that the disease was
chronic, termed ‘bankruptcy disease’, and occurred in farmed trout, with the causal
agent recognised as Cl. botulinum type E. Later, the disease was found on one farm
of rainbow trout in Great Britain (Cann and Taylor 1982 , 1984 ) and was similarly
identifi ed among farmed coho salmon in the USA (Eklund et al. 1982 ), and subsequently associated with channel catfi sh in the USA (Chatla et al. 2012 ).
Characteristic disease symptoms were very vague, but fi sh have been observed to
exhibit abnormal sluggish, erratic swimming, appeared to be listless, and alternately fl oated and sank, before showing temporary rejuvenation. This pattern was
repeated until death eventually ensued (Cann and Taylor 1982 ; Khoo et al. 2011 ;
Beecham et al. 2014 ). Internally, there may be ascites, the brain, spleen and liver
may be congested, vascular dilation, oedema (fl uid retention) in the kidneys and
gastro-intestinal tract, and the blood supply interrupted to the intestines which
appeared to be blanched (Khoo et al. 2011 ). When the swimming speed is adversely
affected, the fi sh are likely to become more prone to predation (Beecham et al.
2014 ).
Isolation/Diagnosis of the Pathogen
Isolation is achieved by use of straightforward anaerobic techniques. Samples of
intestinal contents, which probably support a resident anaerobic microfl ora, and
internal organs should be homogenised in 1 % (w/v) peptone phosphate buffer at
pH 7.0, and diluted fi ve-fold. These diluted samples should be inoculated into
100 ml or 200 ml aliquots of Robertson’s meat broth (see Appendix in Chap. 12 ),
with subsequent anaerobic incubation at 30 °C for up to 6 days. Thereupon, the
presence of Cl. botulinum and its toxicity may be assessed (Cann et al. 1965a , b ;
Cann and Taylor 1982 ). In addition, sterile culture fi ltrates may be injected into
mice and/or fi sh to assess the presence of toxic factors (Cann and Taylor 1982 ).
However, the recovery of Cl. botulinum from intestinal samples should not be used
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)