414
The level of mortality may be extremely high, and fi gures of 60–90 % are not
uncommon. For example, columnaris was considered to be the most important contributing factor for 72.3–97.6 % and 75.4–95.4 % mortality among populations of
adult sockeye salmon and adult chinook salmon, respectively (Fish and Hanavan
1948 ). Similarly, Chen et al. ( 1982 ) reported 77 % and 88.3 % losses among groups
of carp and goldfi sh, respectively. Certainly, there are good data demonstrating the
seasonal effects of mortalities due to columnaris, insofar as Bowser ( 1973 ) reported
60 % infection of bullheads in mid May whereas only a few months later the incidence had dropped to only 10 %.
In addition to water temperature, the severity of columnaris is infl uenced by a
multiplicity of environmental (stress) and host-related factors. Chen et al. ( 1982 )
described the highest eel mortality levels to be associated with stagnant running
water, whereas the lowest losses occurred in running water. Interestingly with aeration, the total losses fell between these two extremes. In this respect, the mortality
rate has been inversely correlated with the level of dissolved oxygen in the water.
Moreover, with adequate dissolved oxygen, deaths increased with a concomitant
rise in the level of ammonia.
Rucker et al. ( 1953 ) isolated highly virulent strains of Fla. columnare, which
were capable of killing fi sh within 24 h, from the water in the upper Columbia River
basin. Furthermore, it has been demonstrated that large numbers of Fla. columnare
cells are present in water during epizootics (McCarthy 1975 ), with good survival
occurring over a wide range of pH and harness values (Fijan 1968 ). Moreover, in
one study, Collins ( 1970 ) reported a relationship between eutrophication and the
numbers of Fla. columnare cells in lake water.
The susceptibility of juvenile Chinook salmon has been correlated with the age
of the fi sh and the stocking density as well as water temperature (Fujihara et al.
1971 ). These workers concluded that rainbow trout of 1 g average weight and
Chinook salmon of 3 g average weight were less susceptible to columnaris than
smaller fi sh. Therefore, it was concluded that age was more important than weight
in determining susceptibility to infection.
Fourteen isolates were recovered from a river by the intake to a fi sh farm and
400 m upstream of the site. One isolate was from a lake without any association
with aquaculture. Generally, these isolates were less virulent than those from a disease outbreak. The isolates survived for months outside of fi sh, and changed their
colony morphology. These data indicate that the pathogen occurs upstream of fi sh
farms, and may be a potential source for outbreaks of disease (Kunttu et al. 2012 ).
Pathogenicity
Initially, Fla. columnare is attracted chemotactically to fi sh mucus (Peatman et al.
2013 ), and grows in and colonises the skin, mucus and gills (Shoemaker and
LaFrentz 2015 ). Certainly, there is a marked variation in the virulence of isolates of
Fla. columnare, with PFGE genetic group A, comprising isolates from channel
7 Flavobacteria and Cytophagas
The level of mortality may be extremely high, and fi gures of 60–90 % are not
uncommon. For example, columnaris was considered to be the most important contributing factor for 72.3–97.6 % and 75.4–95.4 % mortality among populations of
adult sockeye salmon and adult chinook salmon, respectively (Fish and Hanavan
1948 ). Similarly, Chen et al. ( 1982 ) reported 77 % and 88.3 % losses among groups
of carp and goldfi sh, respectively. Certainly, there are good data demonstrating the
seasonal effects of mortalities due to columnaris, insofar as Bowser ( 1973 ) reported
60 % infection of bullheads in mid May whereas only a few months later the incidence had dropped to only 10 %.
In addition to water temperature, the severity of columnaris is infl uenced by a
multiplicity of environmental (stress) and host-related factors. Chen et al. ( 1982 )
described the highest eel mortality levels to be associated with stagnant running
water, whereas the lowest losses occurred in running water. Interestingly with aeration, the total losses fell between these two extremes. In this respect, the mortality
rate has been inversely correlated with the level of dissolved oxygen in the water.
Moreover, with adequate dissolved oxygen, deaths increased with a concomitant
rise in the level of ammonia.
Rucker et al. ( 1953 ) isolated highly virulent strains of Fla. columnare, which
were capable of killing fi sh within 24 h, from the water in the upper Columbia River
basin. Furthermore, it has been demonstrated that large numbers of Fla. columnare
cells are present in water during epizootics (McCarthy 1975 ), with good survival
occurring over a wide range of pH and harness values (Fijan 1968 ). Moreover, in
one study, Collins ( 1970 ) reported a relationship between eutrophication and the
numbers of Fla. columnare cells in lake water.
The susceptibility of juvenile Chinook salmon has been correlated with the age
of the fi sh and the stocking density as well as water temperature (Fujihara et al.
1971 ). These workers concluded that rainbow trout of 1 g average weight and
Chinook salmon of 3 g average weight were less susceptible to columnaris than
smaller fi sh. Therefore, it was concluded that age was more important than weight
in determining susceptibility to infection.
Fourteen isolates were recovered from a river by the intake to a fi sh farm and
400 m upstream of the site. One isolate was from a lake without any association
with aquaculture. Generally, these isolates were less virulent than those from a disease outbreak. The isolates survived for months outside of fi sh, and changed their
colony morphology. These data indicate that the pathogen occurs upstream of fi sh
farms, and may be a potential source for outbreaks of disease (Kunttu et al. 2012 ).
Pathogenicity
Initially, Fla. columnare is attracted chemotactically to fi sh mucus (Peatman et al.
2013 ), and grows in and colonises the skin, mucus and gills (Shoemaker and
LaFrentz 2015 ). Certainly, there is a marked variation in the virulence of isolates of
Fla. columnare, with PFGE genetic group A, comprising isolates from channel
7 Flavobacteria and Cytophagas