7 Genomic Approaches in Aquaculture and Fisheries
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which may be regulated by various hormones. A better understanding of the biological basis for quality traits is therefore of great importance in order to successfully
produce tailor-made seafood in a predictable way.
7.5.2.1 Colour
Muscle colouration is a complex trait and cannot be deduced from external morphology, which has prevented selection using traditional quantitative genetic methods.
This problem has been partially solved in some breeding programs by using scores
from full sibs for breeding value predictions and selection (Gjedrem 2000). Flesh
colour has medium to low heritability in the main fish species. Selective breeding
for this trait is difficult, since phenotypic evaluation requires individuals to be sacrificed for scoring. A single RAPD polymorphism segregating for flesh colour in
Coho salmon was used to derive a molecular single locus SCAR marker (Oki206,
GenBank accession AY661427) associated with muscle colour traits and suggested
as potentially useful in marker-assisted selection (Araneda et al. 2005, Lam et al.
2007). Genetic correlations between muscle carotenoid content and perceived and
colorimetric traits were also lower, suggesting that the retention of pigment is not
under the control of the same genes as perceived colour. It may be that fillet colour
is influenced by factors other than pigment retained in the flesh.
A better understanding of the interaction between carotenoids (e.g. astaxanthin)
and salmon muscle proteins is important to achieve better retention of carotenoid
in salmon flesh. Knowledge regarding the mechanisms associated to astaxanthin
binding to fish muscle is extremely scarce (Matthews et al. 2006). Proteome analysis
of membrane bound astaxanthin transport proteins in adult Atlantic salmon revealed
some up-regulated proteins in response to dietary astaxanthin (Saha 2005). Further
investigations are necessary to elucidate the transport mechanism of astaxanthin
from blood plasma to the muscle proteins.
7.5.2.2 Texture (as Muscle Cellularity)
Texture is one of the major criteria of flesh quality. It is a sensory characteristic
for the consumer and an important attribute for the mechanical processing of fillets.
Because soft texture is frequently reported, the industry is requesting methods able
to measure fish texture, and is also seeking answers to what causes fillet softness.
Textural properties depend both on chemical composition and structural properties,
in particular of myofibrillar and connective tissue proteins. The muscle cellularity
(fiber number and distribution) has been found to affect the texture in fish (Johnston
1999, Kiessling et al. 2006). Intra-species comparison has shown that muscle fibres
measured as average fibre cross-section area, increases with decreasing sensory
firmness in cooked fish (Hurling et al. 1996). Also in fresh and smoked Atlantic
salmon and in fresh brown trout, studies have shown a weak decrease in flesh firmness as the size of the fibres increases (or the fibre density decreases) (Johnston et al.
2004, Bugeon et al. 2003).
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which may be regulated by various hormones. A better understanding of the biological basis for quality traits is therefore of great importance in order to successfully
produce tailor-made seafood in a predictable way.
7.5.2.1 Colour
Muscle colouration is a complex trait and cannot be deduced from external morphology, which has prevented selection using traditional quantitative genetic methods.
This problem has been partially solved in some breeding programs by using scores
from full sibs for breeding value predictions and selection (Gjedrem 2000). Flesh
colour has medium to low heritability in the main fish species. Selective breeding
for this trait is difficult, since phenotypic evaluation requires individuals to be sacrificed for scoring. A single RAPD polymorphism segregating for flesh colour in
Coho salmon was used to derive a molecular single locus SCAR marker (Oki206,
GenBank accession AY661427) associated with muscle colour traits and suggested
as potentially useful in marker-assisted selection (Araneda et al. 2005, Lam et al.
2007). Genetic correlations between muscle carotenoid content and perceived and
colorimetric traits were also lower, suggesting that the retention of pigment is not
under the control of the same genes as perceived colour. It may be that fillet colour
is influenced by factors other than pigment retained in the flesh.
A better understanding of the interaction between carotenoids (e.g. astaxanthin)
and salmon muscle proteins is important to achieve better retention of carotenoid
in salmon flesh. Knowledge regarding the mechanisms associated to astaxanthin
binding to fish muscle is extremely scarce (Matthews et al. 2006). Proteome analysis
of membrane bound astaxanthin transport proteins in adult Atlantic salmon revealed
some up-regulated proteins in response to dietary astaxanthin (Saha 2005). Further
investigations are necessary to elucidate the transport mechanism of astaxanthin
from blood plasma to the muscle proteins.
7.5.2.2 Texture (as Muscle Cellularity)
Texture is one of the major criteria of flesh quality. It is a sensory characteristic
for the consumer and an important attribute for the mechanical processing of fillets.
Because soft texture is frequently reported, the industry is requesting methods able
to measure fish texture, and is also seeking answers to what causes fillet softness.
Textural properties depend both on chemical composition and structural properties,
in particular of myofibrillar and connective tissue proteins. The muscle cellularity
(fiber number and distribution) has been found to affect the texture in fish (Johnston
1999, Kiessling et al. 2006). Intra-species comparison has shown that muscle fibres
measured as average fibre cross-section area, increases with decreasing sensory
firmness in cooked fish (Hurling et al. 1996). Also in fresh and smoked Atlantic
salmon and in fresh brown trout, studies have shown a weak decrease in flesh firmness as the size of the fibres increases (or the fibre density decreases) (Johnston et al.
2004, Bugeon et al. 2003).