431
increasing with time (Decostere et al. 2001 ). Within macrophages, the pathogen is
cytotoxic and resists ROS thereby overcoming the bacterial killing abilities of these
cells. Spleen macrophages were found to have lower antibacterial activity compared
to those from head kidney therefore it was reasoned that the former will be a safer
location for Fla. psychrophilum to exist (Nematollahi et al. 2005a ). Additional evidence has been published that shows that the addition of Fla. psychrophilum cells or
their metabolites to head kidney phagocytes from rainbow trout leads to immediate
oxidative activity as determined by chemiluminescence (Lammens et al. 2000 ).
Furthermore, the ability of isolates to grow in fi sh serum correlates well with pathogenicity, particularly in the case of ayu (Nagai and Nakai 2011 ). There is a clear
relationship between early body weight of rainbow trout and resistance to infection,
but not to genetic diversity of the host (Overturf et al. 2010 ).
The impact of bacteriophage on the host pathogen resulted in a study of four
cultures that were exposed to three virus isolates. Using zebra fi sh, the ancestral
rhizoid morphotype were associated with mortalities of 25–100 %, whereas the
bacteriophage-resistant rough morphotypes that had lost virulence and the ability to
glide did not affect the fi sh. Both morphotypes maintained their colony morphologies over 10- serial passages in broth, except for one low-virulence culture, Os06,
which changed morphology with each passage (Laanto et al. 2012 ).
Also, research has indicated a link between the presence of oxidized lipids in
diets with the development of RTFS (Daskalov et al. 2000 ). In this work fi sh that
were fed with diets containing oxidized lipids developed dystrophic changes in the
kidney, liver and muscle.
A genotyping method analysing two SNPs in the gyrA gene distinguished [ayu]
virulent from avirulent isolates. In total, 232 isolates from four families of fi sh were
equated with four genotypes, G-C, A-T, A-C and G-T, of which the fi rst mentioned
was highly pathogenicity to ayu. Th A-C genotype was at most weakly virulent, but
A-T and G-T types not at all (Fujiwara-Nagata et al. 2012 ).
Disease Control
Management Practices Madsen and Dalsgaard ( 2008 ) were of the opinion that
bore-hole water recirculation systems and good management, i.e. egg disinfection
were important to the control of RTFS infections in rainbow trout. Use of warm
water (28 °C compared with the norm of 18 °C) for 3 days has been successful for
controlling coldwater disease in ayu (Sugahara et al. 2010a ). This was explored
further when protective immunity was found to be induced in ayu by warmed, i.e.
28 °C, water treatment, for 3-days. Thus, ayu subjected to warm water at 1, 6 and
24 h after infection by immersion experienced cumulative mortalities of 36 %, 30 %,
and 18 %, respectively, compared to 90 % mortalties of the controls. Moreover, the
warmed fi sh had higher antibody titres to the pathogen (Sugahara and Eguchi 2012 ).
Flavobacterium psychrophilum
increasing with time (Decostere et al. 2001 ). Within macrophages, the pathogen is
cytotoxic and resists ROS thereby overcoming the bacterial killing abilities of these
cells. Spleen macrophages were found to have lower antibacterial activity compared
to those from head kidney therefore it was reasoned that the former will be a safer
location for Fla. psychrophilum to exist (Nematollahi et al. 2005a ). Additional evidence has been published that shows that the addition of Fla. psychrophilum cells or
their metabolites to head kidney phagocytes from rainbow trout leads to immediate
oxidative activity as determined by chemiluminescence (Lammens et al. 2000 ).
Furthermore, the ability of isolates to grow in fi sh serum correlates well with pathogenicity, particularly in the case of ayu (Nagai and Nakai 2011 ). There is a clear
relationship between early body weight of rainbow trout and resistance to infection,
but not to genetic diversity of the host (Overturf et al. 2010 ).
The impact of bacteriophage on the host pathogen resulted in a study of four
cultures that were exposed to three virus isolates. Using zebra fi sh, the ancestral
rhizoid morphotype were associated with mortalities of 25–100 %, whereas the
bacteriophage-resistant rough morphotypes that had lost virulence and the ability to
glide did not affect the fi sh. Both morphotypes maintained their colony morphologies over 10- serial passages in broth, except for one low-virulence culture, Os06,
which changed morphology with each passage (Laanto et al. 2012 ).
Also, research has indicated a link between the presence of oxidized lipids in
diets with the development of RTFS (Daskalov et al. 2000 ). In this work fi sh that
were fed with diets containing oxidized lipids developed dystrophic changes in the
kidney, liver and muscle.
A genotyping method analysing two SNPs in the gyrA gene distinguished [ayu]
virulent from avirulent isolates. In total, 232 isolates from four families of fi sh were
equated with four genotypes, G-C, A-T, A-C and G-T, of which the fi rst mentioned
was highly pathogenicity to ayu. Th A-C genotype was at most weakly virulent, but
A-T and G-T types not at all (Fujiwara-Nagata et al. 2012 ).
Disease Control
Management Practices Madsen and Dalsgaard ( 2008 ) were of the opinion that
bore-hole water recirculation systems and good management, i.e. egg disinfection
were important to the control of RTFS infections in rainbow trout. Use of warm
water (28 °C compared with the norm of 18 °C) for 3 days has been successful for
controlling coldwater disease in ayu (Sugahara et al. 2010a ). This was explored
further when protective immunity was found to be induced in ayu by warmed, i.e.
28 °C, water treatment, for 3-days. Thus, ayu subjected to warm water at 1, 6 and
24 h after infection by immersion experienced cumulative mortalities of 36 %, 30 %,
and 18 %, respectively, compared to 90 % mortalties of the controls. Moreover, the
warmed fi sh had higher antibody titres to the pathogen (Sugahara and Eguchi 2012 ).
Flavobacterium psychrophilum