224
M.L. Cancela et al.
occur in some shellfish species. This is particularly true for scallop (Martinez and di
Giovanni 2007) but also for the European flat oyster (Lallias et al. 2008). Therefore,
molecular markers can be used to discriminate between selfed and outcrossed
families or individuals within a family.
The choices made at the founding of a breeding programme are critical for its
long term success. This is especially true for the choice of the founder individuals.
Hence lack of adequate base populations is the main reason for the lack of selection response observed in some fish (Gjedrem 2000) and shellfish (Naciri-Graven
et al. 2000). Increasing the effective population size in a breeding programme
will decrease random genetic drift and increase likelihood of showing response to
selection. Molecular markers can be used to infer relatedness between individuals
available as candidate bloodstock to generate the first generation of offspring or at
any level of reproduction in a breeding programme (Hayes et al. 2006), and thereby
avoid mating among close relatives and prevent negative consequences of high levels of inbreeding and genetic load (Gallardo et al. 2004, Camara et al. 2008). Hence,
molecular markers are used on a routine basis to monitor genetic diversity of broodstock of oysters (Hedgecock and Davis 2007), seabream (Blanco et al. 2007), trout
(Was and Wenne 2002, Gross et al. 2007), salmon (Norris et al. 1999, Koljonen et al.
2002, Rengmark et al. 2006), cod (Pampoulie et al. 2006) and flounder (Liu et al.
2005b). Furthermore, in the European flat oyster (Launey et al. 2001) and Japanese
flounder (Sekino et al. 2002), microsatellites were used to demonstrate a loss of
genetic variability in mass selected populations.
Currently, MAS does not yet play a major role in genetic improvement programmes in any of the agricultural sectors, and this is particularly so in aquaculture.
Traditionally, fish and shellfish selective breeding programmes have targeted traits
that can be easily individually recorded and improved using mass selection (body
weight, growth, etc.). However traits that are difficult, expensive or time consuming
to score or that express late in the life of the organism (disease resistance, carcass
quality, feed efficiency, sexual maturation, etc.) may be considered as good candidates to perform MAS in the context of the recent and important development of
molecular markers and high through-put genotyping techniques. Furthermore, compared with genetic modification, the use of MAS is more relaxed, at the level of
research and development, as well as field testing, commercial exchanges, or public
acceptance for which the technology is not an issue.
As a prerequisite for MAS, there must be a known association between genetic
markers and genes affecting the phenotype (trait) of interest. Searching for those
associations corresponds to searching for QTL. To date only two published papers
report the identification of QTLs in shellfish species compared with more than 20
in fish species. For example, in fish, QTLs have been detected affecting cold tolerance and body weight in several species of Oreochromis (Cnaani et al. 2003, Moen
et al. 2004), body weight in salmonids (Reid et al. 2005 and references therein),
disease resistance (Ozaki et al. 2001, Moen et al. 2004, Rodriguez et al. 2004, Khoo
et al. 2004, Cnaani et al. 2004), or upper thermal resistance in salmonids (Somorjai
et al. 2003 and references therein). In shellfish, Yu and Guo (2006) identified QTLs
for resistance to Perkinsus marinus in the American oyster C. virginica and Liu
M.L. Cancela et al.
occur in some shellfish species. This is particularly true for scallop (Martinez and di
Giovanni 2007) but also for the European flat oyster (Lallias et al. 2008). Therefore,
molecular markers can be used to discriminate between selfed and outcrossed
families or individuals within a family.
The choices made at the founding of a breeding programme are critical for its
long term success. This is especially true for the choice of the founder individuals.
Hence lack of adequate base populations is the main reason for the lack of selection response observed in some fish (Gjedrem 2000) and shellfish (Naciri-Graven
et al. 2000). Increasing the effective population size in a breeding programme
will decrease random genetic drift and increase likelihood of showing response to
selection. Molecular markers can be used to infer relatedness between individuals
available as candidate bloodstock to generate the first generation of offspring or at
any level of reproduction in a breeding programme (Hayes et al. 2006), and thereby
avoid mating among close relatives and prevent negative consequences of high levels of inbreeding and genetic load (Gallardo et al. 2004, Camara et al. 2008). Hence,
molecular markers are used on a routine basis to monitor genetic diversity of broodstock of oysters (Hedgecock and Davis 2007), seabream (Blanco et al. 2007), trout
(Was and Wenne 2002, Gross et al. 2007), salmon (Norris et al. 1999, Koljonen et al.
2002, Rengmark et al. 2006), cod (Pampoulie et al. 2006) and flounder (Liu et al.
2005b). Furthermore, in the European flat oyster (Launey et al. 2001) and Japanese
flounder (Sekino et al. 2002), microsatellites were used to demonstrate a loss of
genetic variability in mass selected populations.
Currently, MAS does not yet play a major role in genetic improvement programmes in any of the agricultural sectors, and this is particularly so in aquaculture.
Traditionally, fish and shellfish selective breeding programmes have targeted traits
that can be easily individually recorded and improved using mass selection (body
weight, growth, etc.). However traits that are difficult, expensive or time consuming
to score or that express late in the life of the organism (disease resistance, carcass
quality, feed efficiency, sexual maturation, etc.) may be considered as good candidates to perform MAS in the context of the recent and important development of
molecular markers and high through-put genotyping techniques. Furthermore, compared with genetic modification, the use of MAS is more relaxed, at the level of
research and development, as well as field testing, commercial exchanges, or public
acceptance for which the technology is not an issue.
As a prerequisite for MAS, there must be a known association between genetic
markers and genes affecting the phenotype (trait) of interest. Searching for those
associations corresponds to searching for QTL. To date only two published papers
report the identification of QTLs in shellfish species compared with more than 20
in fish species. For example, in fish, QTLs have been detected affecting cold tolerance and body weight in several species of Oreochromis (Cnaani et al. 2003, Moen
et al. 2004), body weight in salmonids (Reid et al. 2005 and references therein),
disease resistance (Ozaki et al. 2001, Moen et al. 2004, Rodriguez et al. 2004, Khoo
et al. 2004, Cnaani et al. 2004), or upper thermal resistance in salmonids (Somorjai
et al. 2003 and references therein). In shellfish, Yu and Guo (2006) identified QTLs
for resistance to Perkinsus marinus in the American oyster C. virginica and Liu