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M.L. Cancela et al.
due to higher fat content. Moreover, as a result of global limits on the supply of fish
oil, there is a drive to replace dietary fish oils with plant derived oils, which are rich
in C18 PUFA but devoid of the n-3 HUFA abundant in fish oils (Tocher 2003). This
issue has raised concerns over reduced levels of n-3 HUFA in farmed fish, which
could be considered detrimental or likely to compromise the established nutritional
benefits of fish for the consumer.
Experimental evidence suggests that the dependence of marine fish on dietary
HUFA is caused by deficiency in the activity of one or more of the key enzymes, D5
and D6 fatty acid desaturases, and fatty acid elongases, required for HUFA biosynthesis (Tocher 2003). Comparison of genes encoding key elements in the fatty acid
desaturation and elongation pathways between freshwater and marine species is
increasing our knowledge of the molecular genetic basis involved in the modulation
of PUFA biosynthesis in fish. This area is currently the object of intense research
(Zheng et al. 2005, Tocher et al. 2006, Salem et al. 2007, Izquierdo et al. 2008,
Leaver et al. 2008, Panserat et al. 2008a). Although much is known regarding the
composition and catabolism of lipids, the molecular components necessary for the
biogenesis of lipid droplets have remained obscure. Kadereit et al. (2008) reported
the characterization of a conserved gene family important for lipid droplet formation
named fat-inducing transcript (FIT1 and FIT2). Through a morpholino antisense
approach, they showed that by knocking down FIT2 in zebrafish they induced a
blockage of diet-induced accumulation of lipid droplets in intestine and liver, highlighting an important role for FIT2 in lipid droplet formation in vivo. Other genes
of interest for regulating the extent and the pattern of fat deposition, such as lipin-1a
and leptin, are now being studied in farmed animals, including fish (Hanchuan et al.
2006, He et al. 2008).
7.5.3 Other Emerging Quality Traits
As production methods gain importance to many consumers, issues of ethical
production, animal treatment and welfare, and environment-friendly production systems as well as sustainability have more and more influence on seafood product
choices (Harlizius et al. 2004). This “ethical quality” concept of fish is mainly associated with aquaculture products, but sustainable exploitation conditions in the case
of capture fisheries are also gaining importance in seafood markets. This is largely
due to increasing public concern about sustainability issues in the food chain and
anticipated regulatory changes, but also because the welfare standards by which a
fish is reared then slaughtered may produce an impact upon both production and
flesh quality. In general, aquatic animal welfare involves philosophical and ethical
interpretations of humane practices (Håstein et al. 2005). However, physical health
and biological stress indicators are the most universally accepted measures of welfare. An effective health management program must cover all aspects of aquaculture
activity including: real time knowledge of the health status of the fish; identifying
and managing risks to fish health; reducing exposure to or the spread of pathogens;
and managing the use of drugs and/or chemicals (Hill 2005).
M.L. Cancela et al.
due to higher fat content. Moreover, as a result of global limits on the supply of fish
oil, there is a drive to replace dietary fish oils with plant derived oils, which are rich
in C18 PUFA but devoid of the n-3 HUFA abundant in fish oils (Tocher 2003). This
issue has raised concerns over reduced levels of n-3 HUFA in farmed fish, which
could be considered detrimental or likely to compromise the established nutritional
benefits of fish for the consumer.
Experimental evidence suggests that the dependence of marine fish on dietary
HUFA is caused by deficiency in the activity of one or more of the key enzymes, D5
and D6 fatty acid desaturases, and fatty acid elongases, required for HUFA biosynthesis (Tocher 2003). Comparison of genes encoding key elements in the fatty acid
desaturation and elongation pathways between freshwater and marine species is
increasing our knowledge of the molecular genetic basis involved in the modulation
of PUFA biosynthesis in fish. This area is currently the object of intense research
(Zheng et al. 2005, Tocher et al. 2006, Salem et al. 2007, Izquierdo et al. 2008,
Leaver et al. 2008, Panserat et al. 2008a). Although much is known regarding the
composition and catabolism of lipids, the molecular components necessary for the
biogenesis of lipid droplets have remained obscure. Kadereit et al. (2008) reported
the characterization of a conserved gene family important for lipid droplet formation
named fat-inducing transcript (FIT1 and FIT2). Through a morpholino antisense
approach, they showed that by knocking down FIT2 in zebrafish they induced a
blockage of diet-induced accumulation of lipid droplets in intestine and liver, highlighting an important role for FIT2 in lipid droplet formation in vivo. Other genes
of interest for regulating the extent and the pattern of fat deposition, such as lipin-1a
and leptin, are now being studied in farmed animals, including fish (Hanchuan et al.
2006, He et al. 2008).
7.5.3 Other Emerging Quality Traits
As production methods gain importance to many consumers, issues of ethical
production, animal treatment and welfare, and environment-friendly production systems as well as sustainability have more and more influence on seafood product
choices (Harlizius et al. 2004). This “ethical quality” concept of fish is mainly associated with aquaculture products, but sustainable exploitation conditions in the case
of capture fisheries are also gaining importance in seafood markets. This is largely
due to increasing public concern about sustainability issues in the food chain and
anticipated regulatory changes, but also because the welfare standards by which a
fish is reared then slaughtered may produce an impact upon both production and
flesh quality. In general, aquatic animal welfare involves philosophical and ethical
interpretations of humane practices (Håstein et al. 2005). However, physical health
and biological stress indicators are the most universally accepted measures of welfare. An effective health management program must cover all aspects of aquaculture
activity including: real time knowledge of the health status of the fish; identifying
and managing risks to fish health; reducing exposure to or the spread of pathogens;
and managing the use of drugs and/or chemicals (Hill 2005).