206
J.G. Bell and R. Waagbø
Besides being rich in calcium, fish products contain considerable amounts of
iodine (I) and selenium (Se) that can contribute a significant part of the human
recommended daily intakes. It is possible to tailor fillet Se concentration by dietary
supplementation in salmonids, however both the retained form and efficacy of
retention depends on the dietary chemical form of the element (Bell and Cowey
1989; Lorentzen et al. 1994). It also appears that the bioavailability of Se, as
observed in rats (Ørnsrud and Lorentzen 2002), and the benefits of Se in human
nutrition and health depend upon the chemical form supplied (Drake 2006). For example, the oxidative nature of selenite seems to exert higher cancer chemopreventive
effects than the amino acid forms, selenomethionine and Se-methyl-selenocysteine,
which lack oxidation capability (Drake 2006). FM contains considerably more
Se compared to soybean meal (Table 6.3). Recently, Polatajko et al. (2006) reviewed
the complexity of chemical Se species in biological samples. In this regard, speciation of Se in feed and food is necessary to evaluate risks and benefits of using FM
substitutes, in addition to considering the total Se content (Table 6.3).
Iodine deficiency disorders, such as goitre, hypothyroidism, cretinism and related
mental effects occur frequently in humans, especially in developing countries, with
estimates of 1 billion at risk (Hetzel and Clugston 1999). Fish and seaweed are
among the food items with the highest naturally occurring iodine contents, however,
there is large variation among fish species and even between individuals. Despite
relatively low levels in salmonids, it has recently been demonstrated that it is possible to increase fillet iodine levels three fold in adult Atlantic salmon farmed in seawater (from 0.25 to 0.9 mg I kg
−1 wet weight) by feeding diets supplemented with
high levels of an iodine salt (0–80 mg I kg
−1
) (Julshamn et al. 2006). Freshwater char
(Salvelinus sp.) seem to respond in a similar range when using a marine algae in the
feed (fillet conc. 0.14 to 0.54 mg I kg
−1 wet weight) (Schmid et al. 2003). Other species show higher levels of fillet iodine, for example, wild caught Atlantic cod
(Gadus morhua) from the Barents Sea, range between 0.34 and 12.7 mg I kg
−1 (Julshamn
et al. 2001), and may be an even better species for tailoring muscle iodine content
than Atlantic salmon. Replacing FM with plant meals may introduce variations in
fillet iodine content, even though the minimum iodine requirement for growth of fish
(1 mg/kg diet; National Research Council 1993) may easily be covered through
uptake from seawater and diet (Lall 2002).
6.8.2 Fish Oil and Fish Meal Substitutes – Consequences
for Lipid Soluble Vitamins A and D
Fish are among the few natural sources of vitamins A and D, originating from the
lower trophic levels in the marine food web. Fish species with oily flesh, like the
salmonids, contain considerable amounts of vitamin D in their fillets (Ostermeyer
and Schmidt 2006) and less vitamin A, while lean fish species normally have higher
concentrations of fat soluble vitamins in their liver stores (for example, cod liver oil
used as human vitamin A and D supplements). FO-based aquafeeds normally supply
J.G. Bell and R. Waagbø
Besides being rich in calcium, fish products contain considerable amounts of
iodine (I) and selenium (Se) that can contribute a significant part of the human
recommended daily intakes. It is possible to tailor fillet Se concentration by dietary
supplementation in salmonids, however both the retained form and efficacy of
retention depends on the dietary chemical form of the element (Bell and Cowey
1989; Lorentzen et al. 1994). It also appears that the bioavailability of Se, as
observed in rats (Ørnsrud and Lorentzen 2002), and the benefits of Se in human
nutrition and health depend upon the chemical form supplied (Drake 2006). For example, the oxidative nature of selenite seems to exert higher cancer chemopreventive
effects than the amino acid forms, selenomethionine and Se-methyl-selenocysteine,
which lack oxidation capability (Drake 2006). FM contains considerably more
Se compared to soybean meal (Table 6.3). Recently, Polatajko et al. (2006) reviewed
the complexity of chemical Se species in biological samples. In this regard, speciation of Se in feed and food is necessary to evaluate risks and benefits of using FM
substitutes, in addition to considering the total Se content (Table 6.3).
Iodine deficiency disorders, such as goitre, hypothyroidism, cretinism and related
mental effects occur frequently in humans, especially in developing countries, with
estimates of 1 billion at risk (Hetzel and Clugston 1999). Fish and seaweed are
among the food items with the highest naturally occurring iodine contents, however,
there is large variation among fish species and even between individuals. Despite
relatively low levels in salmonids, it has recently been demonstrated that it is possible to increase fillet iodine levels three fold in adult Atlantic salmon farmed in seawater (from 0.25 to 0.9 mg I kg
−1 wet weight) by feeding diets supplemented with
high levels of an iodine salt (0–80 mg I kg
−1
) (Julshamn et al. 2006). Freshwater char
(Salvelinus sp.) seem to respond in a similar range when using a marine algae in the
feed (fillet conc. 0.14 to 0.54 mg I kg
−1 wet weight) (Schmid et al. 2003). Other species show higher levels of fillet iodine, for example, wild caught Atlantic cod
(Gadus morhua) from the Barents Sea, range between 0.34 and 12.7 mg I kg
−1 (Julshamn
et al. 2001), and may be an even better species for tailoring muscle iodine content
than Atlantic salmon. Replacing FM with plant meals may introduce variations in
fillet iodine content, even though the minimum iodine requirement for growth of fish
(1 mg/kg diet; National Research Council 1993) may easily be covered through
uptake from seawater and diet (Lall 2002).
6.8.2 Fish Oil and Fish Meal Substitutes – Consequences
for Lipid Soluble Vitamins A and D
Fish are among the few natural sources of vitamins A and D, originating from the
lower trophic levels in the marine food web. Fish species with oily flesh, like the
salmonids, contain considerable amounts of vitamin D in their fillets (Ostermeyer
and Schmidt 2006) and less vitamin A, while lean fish species normally have higher
concentrations of fat soluble vitamins in their liver stores (for example, cod liver oil
used as human vitamin A and D supplements). FO-based aquafeeds normally supply