397
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_7
Chapter 7
Flavobacteria and Cytophagas
Abstract An increasing number of Gram-negative chromogens have become associated with fi sh diseases particularly involving the gills and external surfaces [fi n/
tail rot]. New additions to the list of pathogens include Chryseobacterium piscicola,
Flavobacterium oncorhynchi, Tenacibaculum dicentrarchi, T. discolor, T. gallaicum
and T. soleae with research interest focusing on molecular diagnoses and disease
control by vaccination, probiotics, immunostimulants and bacteriophages.
Keywords Gill disease • Flavobacteriosis • RTFS • Coldwater disease • Columnaris
Numerous reports have centred around the role of Gram-negative chromogens as
agents of fi sh disease, particularly associated with gill disease involving hyperplasia, hypertrophy and fusion of the gill lamellae (Fig. 7.1 ). Genera that have been
mentioned frequently include Cytophaga, Flavobacterium, Flexibacter,
Myxobacterium, Myxococcus and Sporocytophaga. The common factor is that these
genera comprise diffi cult-to-identify species, a taxonomic re-evaluation of which
has at long last occurred. Moreover from the early literature it is often uncertain into
which of these genera unknown isolates should have been placed. In particular, the
distinction between Cytophaga and Flexibacter was confusing (Christensen 1977 ;
Allen et al. 1983 ). The authenticity of Flavobacterium has been questioned repeatedly, insofar as it became a recipient of problematical pigmented bacteria.
Fortunately, more recent work has improved the taxonomy of Flavobacterium
(Holmes et al. 1984 ; Bernardet et al. 1996 ). Myxobacterium, considered to be a
causal agent of gill disease (Ghittino 1967 ; Wood 1968 ; Bullock and McLaughlin
1970 ; Ashburner 1978 ), is not included in the ‘Approved Lists of Bacterial Names’
(Skerman et al. 1980 ) or their supplements. Therefore, this genus lacks taxonomic
meaning. It is possible that the organisms, identifi ed as Myxobacterium (and referred
to as myxobacters), belong in either Cytophaga, Flavobacterium or Flexibacter.
Historically, interest in chromogenic Gram-negative bacteria started with a publication by Davis ( 1922 ), who reported serious mortalities (columnaris) among
warm-water fi sh, namely small mouth bass and common perch, from the Mississippi
River. These fi sh were held at the US Biological Station at Fairport, Iowa, when the
disease occurred. Davis recognised two important features of the disease, namely
that occurrence was primarily in injured (damaged/stressed) fi sh, and that the water
temperature was high, i.e. >21.1 °C. Unfortunately, Davis did not succeed in isolat-
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_7
Chapter 7
Flavobacteria and Cytophagas
Abstract An increasing number of Gram-negative chromogens have become associated with fi sh diseases particularly involving the gills and external surfaces [fi n/
tail rot]. New additions to the list of pathogens include Chryseobacterium piscicola,
Flavobacterium oncorhynchi, Tenacibaculum dicentrarchi, T. discolor, T. gallaicum
and T. soleae with research interest focusing on molecular diagnoses and disease
control by vaccination, probiotics, immunostimulants and bacteriophages.
Keywords Gill disease • Flavobacteriosis • RTFS • Coldwater disease • Columnaris
Numerous reports have centred around the role of Gram-negative chromogens as
agents of fi sh disease, particularly associated with gill disease involving hyperplasia, hypertrophy and fusion of the gill lamellae (Fig. 7.1 ). Genera that have been
mentioned frequently include Cytophaga, Flavobacterium, Flexibacter,
Myxobacterium, Myxococcus and Sporocytophaga. The common factor is that these
genera comprise diffi cult-to-identify species, a taxonomic re-evaluation of which
has at long last occurred. Moreover from the early literature it is often uncertain into
which of these genera unknown isolates should have been placed. In particular, the
distinction between Cytophaga and Flexibacter was confusing (Christensen 1977 ;
Allen et al. 1983 ). The authenticity of Flavobacterium has been questioned repeatedly, insofar as it became a recipient of problematical pigmented bacteria.
Fortunately, more recent work has improved the taxonomy of Flavobacterium
(Holmes et al. 1984 ; Bernardet et al. 1996 ). Myxobacterium, considered to be a
causal agent of gill disease (Ghittino 1967 ; Wood 1968 ; Bullock and McLaughlin
1970 ; Ashburner 1978 ), is not included in the ‘Approved Lists of Bacterial Names’
(Skerman et al. 1980 ) or their supplements. Therefore, this genus lacks taxonomic
meaning. It is possible that the organisms, identifi ed as Myxobacterium (and referred
to as myxobacters), belong in either Cytophaga, Flavobacterium or Flexibacter.
Historically, interest in chromogenic Gram-negative bacteria started with a publication by Davis ( 1922 ), who reported serious mortalities (columnaris) among
warm-water fi sh, namely small mouth bass and common perch, from the Mississippi
River. These fi sh were held at the US Biological Station at Fairport, Iowa, when the
disease occurred. Davis recognised two important features of the disease, namely
that occurrence was primarily in injured (damaged/stressed) fi sh, and that the water
temperature was high, i.e. >21.1 °C. Unfortunately, Davis did not succeed in isolat-