247
established that the pathogen survived up to 6 days on both dry and wet contaminated nets. In addition, wet and dry contaminated netting was disinfected using
three compounds, i.e. acrifl avine, Teepol-sodium hydroxide and hypochlorite solutions. Aer. salmonicida was not recovered from either wet or dry netting disinfected
with the acrifl avine or Teepol-sodium hydroxide solutions, but the hypochlorite
solution failed to disinfect dry nets. McCarthy ( 1980 ) concluded from these results
that the use of contaminated and improperly disinfected nets is potentially dangerous to healthy stock as it is known that netting abrades fi sh to some extent, and such
abrasions can facilitate bacterial invasion. In addition, Aer. salmonicida has been
reported to attach in higher numbers to plastic rather than stainless steel surfaces,
which opens up the possibility that the pathogen may have a preference for certain
substrates/surfaces in the aquaculture environment (Carballo et al. 2000 ).
More recently, it has been found that wrasse (these are small inshore benthic fi sh
which have gained popularity as a means of controlling sea lice populations among
infested Atlantic salmon) are also susceptible to furunculosis (Treasurer and Cox
1991 ). These investigators reported the recovery of typical Aer. salmonicida from
the liver and kidney, and the presence of skin lesions reminiscent of chronic furunculosis in golsinny, rock cook and cuckoo wrasse of fi sh farm origin. But could
salmon lice harbour and transmit Aer. salmonicida? By means of recovery techniques with immunomagnetic beads coated with monoclonal antibodies to LPS and
culturing techniques, it was determined that Aer. salmonicida was recoverable from
lice (~10
4 Aer. salmonicida cells/louse) and also marine plankton 600 Aer. salmonicida cells/g of homogenised plankton) (Nese and Enger 1993 ). Perhaps more worrisome is the report by Frerichs et al. ( 1992 ) of the recovery of atypical Aer.
salmonicida from apparently healthy wild wrasse captured in the open sea.
Fortunately in this instance, the isolates were proven to be non-pathogenic to
Atlantic salmon smolts. Consequently, both groups have cautioned against the arbitrary stocking of wrasse in fi sh farms without fi rst checking for the possible presence of Aer. salmonicida in the fi sh. Furthermore, Treasurer and Cox ( 1991 )
recommended that wrasse should not be released back into the wild, or transferred
between fi sh farms at the end of the production cycle.
Only a few investigators have examined animals, other than fi sh, as a potential
source of infection. The extensive study carried out on this topic was that of Cornick
et al. ( 1969 ); a total of 2954 vertebrate and invertebrate specimens, collected from
fi sh ponds during an epizootic of furunculosis, were examined for the presence of
Aer. salmonicida. No isolates of the pathogen were recovered despite this heroic
attempt. This study is cited time and time again as evidence against the likelihood
of animals, other than fi sh, acting as reservoirs of infection. Williamson ( 1928 ) was
also unsuccessful in isolating the pathogen from water snails under similar conditions. Allen ( 1982 ) examined macroscopic algae and zooplankton taken from fi sh
tanks prior to, during, and after a furunculosis epizootic at a fi sh-rearing unit in
Essex, UK, in an unsuccessful attempt to recover Aer. salmonicida from these
organisms. In contrast, King and Shotts ( 1988 ) determined that viable cells of Aer.
salmonicida survived and, indeed, multiplied (two-fold) within the digestive tract of
the ciliated protozoan, Tetrahymena pyriformis. It may be concluded from some of
Aeromonas salmonicida
established that the pathogen survived up to 6 days on both dry and wet contaminated nets. In addition, wet and dry contaminated netting was disinfected using
three compounds, i.e. acrifl avine, Teepol-sodium hydroxide and hypochlorite solutions. Aer. salmonicida was not recovered from either wet or dry netting disinfected
with the acrifl avine or Teepol-sodium hydroxide solutions, but the hypochlorite
solution failed to disinfect dry nets. McCarthy ( 1980 ) concluded from these results
that the use of contaminated and improperly disinfected nets is potentially dangerous to healthy stock as it is known that netting abrades fi sh to some extent, and such
abrasions can facilitate bacterial invasion. In addition, Aer. salmonicida has been
reported to attach in higher numbers to plastic rather than stainless steel surfaces,
which opens up the possibility that the pathogen may have a preference for certain
substrates/surfaces in the aquaculture environment (Carballo et al. 2000 ).
More recently, it has been found that wrasse (these are small inshore benthic fi sh
which have gained popularity as a means of controlling sea lice populations among
infested Atlantic salmon) are also susceptible to furunculosis (Treasurer and Cox
1991 ). These investigators reported the recovery of typical Aer. salmonicida from
the liver and kidney, and the presence of skin lesions reminiscent of chronic furunculosis in golsinny, rock cook and cuckoo wrasse of fi sh farm origin. But could
salmon lice harbour and transmit Aer. salmonicida? By means of recovery techniques with immunomagnetic beads coated with monoclonal antibodies to LPS and
culturing techniques, it was determined that Aer. salmonicida was recoverable from
lice (~10
4 Aer. salmonicida cells/louse) and also marine plankton 600 Aer. salmonicida cells/g of homogenised plankton) (Nese and Enger 1993 ). Perhaps more worrisome is the report by Frerichs et al. ( 1992 ) of the recovery of atypical Aer.
salmonicida from apparently healthy wild wrasse captured in the open sea.
Fortunately in this instance, the isolates were proven to be non-pathogenic to
Atlantic salmon smolts. Consequently, both groups have cautioned against the arbitrary stocking of wrasse in fi sh farms without fi rst checking for the possible presence of Aer. salmonicida in the fi sh. Furthermore, Treasurer and Cox ( 1991 )
recommended that wrasse should not be released back into the wild, or transferred
between fi sh farms at the end of the production cycle.
Only a few investigators have examined animals, other than fi sh, as a potential
source of infection. The extensive study carried out on this topic was that of Cornick
et al. ( 1969 ); a total of 2954 vertebrate and invertebrate specimens, collected from
fi sh ponds during an epizootic of furunculosis, were examined for the presence of
Aer. salmonicida. No isolates of the pathogen were recovered despite this heroic
attempt. This study is cited time and time again as evidence against the likelihood
of animals, other than fi sh, acting as reservoirs of infection. Williamson ( 1928 ) was
also unsuccessful in isolating the pathogen from water snails under similar conditions. Allen ( 1982 ) examined macroscopic algae and zooplankton taken from fi sh
tanks prior to, during, and after a furunculosis epizootic at a fi sh-rearing unit in
Essex, UK, in an unsuccessful attempt to recover Aer. salmonicida from these
organisms. In contrast, King and Shotts ( 1988 ) determined that viable cells of Aer.
salmonicida survived and, indeed, multiplied (two-fold) within the digestive tract of
the ciliated protozoan, Tetrahymena pyriformis. It may be concluded from some of
Aeromonas salmonicida