234
M.L. Cancela et al.
The muscle fibre number in mammals and avian species is determined by prenatal events (maternal nutrition, bioactive agents, abiotic factors, breed and genotype),
but in fish it is also affected by factors post hatching (Johnston 2006). Although the
cell biology of myogenesis in teleosts is distinct from that described in mammals,
the genes involved in growth regulation are apparently highly conserved (Watabe
2001). The completion of the genome sequences of the Japanese pufferfish (Takifugu
rubripes) and the zebrafish (Danio rerio) provide new opportunities for understanding the molecular regulation of post-embryonic muscle growth. The zebrafish
periostin gene was recently found to be important for the adhesion of muscle fiber
bundles to the myoseptum and for the differentiation of muscle fibers (Kudo et al.
2004). In rodents, periostin (also named osteoblast-specific factor 2 or Osf2) was
found to be strongly upregulated during the muscle regeneration process (Goetsch
et al. 2003), and has been considered a candidate gene for enhanced muscle growth
in pigs (Bílek et al. 2008). Its potential as a flesh quality trait still remains to be
assessed in fish.
Such studies have considerable economic importance in aquaculture since the
plasticity of muscle growth under different production conditions is a major factor in determining quality, in particular the texture and processing characteristics
of the flesh (Johnston 1999). Furthermore, since the vast majority of teleosts are
ectothermic with external fertilisation, environmental factors have far more impact
on muscle growth than in mammals (Johnston 2006).
7.5.2.3 Texture (as Affected by Postmortem Degradation)
The texture of fish fillets undergoes rapid changes in the post-mortem stage. A vast
body of literature shows that texture, measured as shear force, varies also with farming practices including harvesting stress, slaughter method, dietary factors, storage
time and storage temperature (Sigholt et al. 1997, Johnston et al. 2002, Bencze-Røra
et al. 2003, Bugeon et al. 2003, Espe et al. 2004). Despite a large bibliography on
degradation patterns during post-mortem storage of fish, many uncertainties remain
regarding how degradation of specific proteins relates to flesh firmness.
A detailed characterisation of post-mortem changes in fish muscle would benefit
from experimental approaches and technologies aimed at parallel analysis of numerous genes and proteins simultaneously. Genomic and proteomic technologies offer
a comprehensive approach to study biochemical systems by expanding the investigation from single to multiple genes/proteins simultaneously. Recently, a subtracted
cDNA library was used to identify specific genes whose expression is increased in
post-mortem muscle of rainbow trout (Oncorhynchus mykiss) during on-ice storage (Saito et al. 2006). Of the 200 cDNAs analyzed, 82 had significant homologies
to other previously identified fish genes such as troponin I and glyceraldehyde-3phosphate dehydrogenase (GAPDH). Comparison of gene expression profiles by
dot blot hybridization confirmed an increase of mRNA in muscle after 3 h of onice storage compared to that at 0 h after death. Real-time reverse transcriptase-PCR
analysis indicated that the cells of muscle tissues are able to synthesize troponin I
and GAPDH mRNAs for at least 24 h, and maybe up to 48 h, in fish kept on ice.
M.L. Cancela et al.
The muscle fibre number in mammals and avian species is determined by prenatal events (maternal nutrition, bioactive agents, abiotic factors, breed and genotype),
but in fish it is also affected by factors post hatching (Johnston 2006). Although the
cell biology of myogenesis in teleosts is distinct from that described in mammals,
the genes involved in growth regulation are apparently highly conserved (Watabe
2001). The completion of the genome sequences of the Japanese pufferfish (Takifugu
rubripes) and the zebrafish (Danio rerio) provide new opportunities for understanding the molecular regulation of post-embryonic muscle growth. The zebrafish
periostin gene was recently found to be important for the adhesion of muscle fiber
bundles to the myoseptum and for the differentiation of muscle fibers (Kudo et al.
2004). In rodents, periostin (also named osteoblast-specific factor 2 or Osf2) was
found to be strongly upregulated during the muscle regeneration process (Goetsch
et al. 2003), and has been considered a candidate gene for enhanced muscle growth
in pigs (Bílek et al. 2008). Its potential as a flesh quality trait still remains to be
assessed in fish.
Such studies have considerable economic importance in aquaculture since the
plasticity of muscle growth under different production conditions is a major factor in determining quality, in particular the texture and processing characteristics
of the flesh (Johnston 1999). Furthermore, since the vast majority of teleosts are
ectothermic with external fertilisation, environmental factors have far more impact
on muscle growth than in mammals (Johnston 2006).
7.5.2.3 Texture (as Affected by Postmortem Degradation)
The texture of fish fillets undergoes rapid changes in the post-mortem stage. A vast
body of literature shows that texture, measured as shear force, varies also with farming practices including harvesting stress, slaughter method, dietary factors, storage
time and storage temperature (Sigholt et al. 1997, Johnston et al. 2002, Bencze-Røra
et al. 2003, Bugeon et al. 2003, Espe et al. 2004). Despite a large bibliography on
degradation patterns during post-mortem storage of fish, many uncertainties remain
regarding how degradation of specific proteins relates to flesh firmness.
A detailed characterisation of post-mortem changes in fish muscle would benefit
from experimental approaches and technologies aimed at parallel analysis of numerous genes and proteins simultaneously. Genomic and proteomic technologies offer
a comprehensive approach to study biochemical systems by expanding the investigation from single to multiple genes/proteins simultaneously. Recently, a subtracted
cDNA library was used to identify specific genes whose expression is increased in
post-mortem muscle of rainbow trout (Oncorhynchus mykiss) during on-ice storage (Saito et al. 2006). Of the 200 cDNAs analyzed, 82 had significant homologies
to other previously identified fish genes such as troponin I and glyceraldehyde-3phosphate dehydrogenase (GAPDH). Comparison of gene expression profiles by
dot blot hybridization confirmed an increase of mRNA in muscle after 3 h of onice storage compared to that at 0 h after death. Real-time reverse transcriptase-PCR
analysis indicated that the cells of muscle tissues are able to synthesize troponin I
and GAPDH mRNAs for at least 24 h, and maybe up to 48 h, in fish kept on ice.