148
1
Introduction
It is well known that fi shing and aquaculture are
very important to world food production. World
market demand for high quality products has
stimulated much of the growth in aquaculture,
especially for salmonid, shrimp, and shellfi sh
species (Nakano 2007 ). Cultured fi sh are exposed
to biotic and abiotic stressors, such as toxicants
and acute changes in temperature, which can
increase the chances of these fi sh succumbing to
infectious disease (Pickering 1993 ; Nakano and
Takeuchi 1997 ; Nakano et al. 1999a ; Iwama et al.
2006 ; Nakano 2007 , 2011 ; Pankhurst 2011 ; Ellis
et al. 2012 ; Prunet et al. 2012 ). Furthermore,
perturbations due to global climate change,
typhoon, tsunami, and artifi cial factors such as
environmental pollutants, radioactive contaminants derived from nuclear power plant accident,
in aquatic biological systems have recently
become a serious problem (Pörtner 2002 ; Lesser
2006 ; Valavanidis et al. 2006 ; Hofmann and
Todgham 2010 ; Urushihara 2013 ; Hara 2014 ).
In response to a particular stressor, a series of
biochemical and physiological changes occur at
both the cellular and organismal levels. These
stress responses in fi sh can affect their general
health, disease resistance, growth, and reproduction (Barton and Iwama 1991 ; Pickering 1993 ;
Pickering and Pottinger 1995 ; Pankhurst and
Kraak 1997 ; Barton 1997 ; Nakano 2011 ; Prunet
et al. 2012 ).
The growth of fi sh is regulated to a large extent
by liver-derived insulin-like growth factor
(IGF)-1 in response to pituitary-secreted growth
hormone (GH) binding to GH receptor (GHR) in
the liver. The GH-IGF-1 axis has a critical role in
regulating both fi sh growth and development
(Kopchick and Andry 2000 ; Moriyama et al.
2000 ; Björnsson et al. 2002 ; Reineck et al. 2005 ;
Klein and Sheridan 2008 ; Deane and Woo 2009 ;
Reineck 2010 ).
Fish growth is genetically regulated and is
also infl uenced by cellular, endocrinological, and
environmental factors. The responses of endocrine tissue are affected by the integration of
external stimuli with internal signals according to
the physiological state (Peter 1979 ; Barton and
Iwama 1991 ; Pickering 1993 ; Pickering and
Pottinger 1995 ; Duan 1998 ; Moriyama et al.
2000 ; Mommsen and Moon 2001 ; Iwama et al.
2006 ; Kameda et al. 2008 ; Deane and Woo 2009 ;
Reineck 2010 ; Nakano 2011 ; Prunet et al. 2012 ).
The physiological states of ectothermal organisms, such as fi sh, depend on the environmental
temperature. Studies on thermal stress in fi sh
have primarily focused on cellular molecular
chaperones, heat shock proteins (HSPs), expression, and characterization (Iwama et al. 1998 ;
Feder and Hofmann 1999 ; Basu et al. 2001 , 2002 ;
Pörtner 2002 ; Nakano 2011 ; Iwama et al. 2006 ).
Little is known about the effects of severe acute
stressors, such as heat shock, on the expression
levels of genes that are related to growth in fi sh
(Pörtner 2002 ; Lushchak and Bagnyukova 2006a ;
Kameda et al. 2008 ; Deane and Woo 2009 ;
Reineck 2010 ; Nakano 2011 ; Beckman 2011 ;
Nakano et al. 2013 , 2014 ). Therefore, it is important to determine the effects of thermal stress on
fi sh fi tness and tolerance in order to improve their
production and health in both natural and cultural
conditions.
In this study, we examined changes in mRNA
expression levels of the gh, ghr, and igf1 genes in
response to a severe acute stress derived from heat
shock in coho salmon ( Oncorhynchus kisutch ).
Coho salmon is known to be one of the most valued species used in aquaculture. We discuss the
relationships between the thermal stress responses,
expressions of growth-related genes, and the oxidative stress in fi sh in the context of our fi ndings.
2
Materials and Methods
2.1
Fish, Rearing Conditions,
Stress Performance,
and Sampling
Coho salmon were purchased from a local
hatchery, Sakai Hatchery Co., in Zao town,
T. Nakano et al.
1
Introduction
It is well known that fi shing and aquaculture are
very important to world food production. World
market demand for high quality products has
stimulated much of the growth in aquaculture,
especially for salmonid, shrimp, and shellfi sh
species (Nakano 2007 ). Cultured fi sh are exposed
to biotic and abiotic stressors, such as toxicants
and acute changes in temperature, which can
increase the chances of these fi sh succumbing to
infectious disease (Pickering 1993 ; Nakano and
Takeuchi 1997 ; Nakano et al. 1999a ; Iwama et al.
2006 ; Nakano 2007 , 2011 ; Pankhurst 2011 ; Ellis
et al. 2012 ; Prunet et al. 2012 ). Furthermore,
perturbations due to global climate change,
typhoon, tsunami, and artifi cial factors such as
environmental pollutants, radioactive contaminants derived from nuclear power plant accident,
in aquatic biological systems have recently
become a serious problem (Pörtner 2002 ; Lesser
2006 ; Valavanidis et al. 2006 ; Hofmann and
Todgham 2010 ; Urushihara 2013 ; Hara 2014 ).
In response to a particular stressor, a series of
biochemical and physiological changes occur at
both the cellular and organismal levels. These
stress responses in fi sh can affect their general
health, disease resistance, growth, and reproduction (Barton and Iwama 1991 ; Pickering 1993 ;
Pickering and Pottinger 1995 ; Pankhurst and
Kraak 1997 ; Barton 1997 ; Nakano 2011 ; Prunet
et al. 2012 ).
The growth of fi sh is regulated to a large extent
by liver-derived insulin-like growth factor
(IGF)-1 in response to pituitary-secreted growth
hormone (GH) binding to GH receptor (GHR) in
the liver. The GH-IGF-1 axis has a critical role in
regulating both fi sh growth and development
(Kopchick and Andry 2000 ; Moriyama et al.
2000 ; Björnsson et al. 2002 ; Reineck et al. 2005 ;
Klein and Sheridan 2008 ; Deane and Woo 2009 ;
Reineck 2010 ).
Fish growth is genetically regulated and is
also infl uenced by cellular, endocrinological, and
environmental factors. The responses of endocrine tissue are affected by the integration of
external stimuli with internal signals according to
the physiological state (Peter 1979 ; Barton and
Iwama 1991 ; Pickering 1993 ; Pickering and
Pottinger 1995 ; Duan 1998 ; Moriyama et al.
2000 ; Mommsen and Moon 2001 ; Iwama et al.
2006 ; Kameda et al. 2008 ; Deane and Woo 2009 ;
Reineck 2010 ; Nakano 2011 ; Prunet et al. 2012 ).
The physiological states of ectothermal organisms, such as fi sh, depend on the environmental
temperature. Studies on thermal stress in fi sh
have primarily focused on cellular molecular
chaperones, heat shock proteins (HSPs), expression, and characterization (Iwama et al. 1998 ;
Feder and Hofmann 1999 ; Basu et al. 2001 , 2002 ;
Pörtner 2002 ; Nakano 2011 ; Iwama et al. 2006 ).
Little is known about the effects of severe acute
stressors, such as heat shock, on the expression
levels of genes that are related to growth in fi sh
(Pörtner 2002 ; Lushchak and Bagnyukova 2006a ;
Kameda et al. 2008 ; Deane and Woo 2009 ;
Reineck 2010 ; Nakano 2011 ; Beckman 2011 ;
Nakano et al. 2013 , 2014 ). Therefore, it is important to determine the effects of thermal stress on
fi sh fi tness and tolerance in order to improve their
production and health in both natural and cultural
conditions.
In this study, we examined changes in mRNA
expression levels of the gh, ghr, and igf1 genes in
response to a severe acute stress derived from heat
shock in coho salmon ( Oncorhynchus kisutch ).
Coho salmon is known to be one of the most valued species used in aquaculture. We discuss the
relationships between the thermal stress responses,
expressions of growth-related genes, and the oxidative stress in fi sh in the context of our fi ndings.
2
Materials and Methods
2.1
Fish, Rearing Conditions,
Stress Performance,
and Sampling
Coho salmon were purchased from a local
hatchery, Sakai Hatchery Co., in Zao town,
T. Nakano et al.