6 Safe and Nutritious Aquaculture Produce
189
fish species that could be used directly as food for humans, in animal feeds (Tacon
1997; Goldburg and Naylor 2005). Furthermore, there is also heightened public and
non-governmental organisations (NGO) awareness over the management of feed
grade fisheries and the potential impact on marine ecosystems particularly effects
on sea birds and marine mammals (Huntington et al. 2004).
A further reason to substitute FO for VO in fish diets is that carnivorous fish
have evolved to use oil for the energy required to fuel growth and reproduction.
Thus, in effect, most of the oil consumed by fish is effectively “burned” to supply
energy and fish do not seem to discriminate greatly between which fatty acids are
retained and which are metabolised. Therefore, once essential fatty acid requirements
have been met the excess n-3 PUFA in FO are stored as triacylglycerols in body
stores and then used for energy production (Sargent et al. 2002). For that reason, it
might be more productive to feed VO for energy production, in place of FO, for
most of the production cycle and not waste valuable n-3 HUFA in the production
of energy for growth. Further, the use of FO finishing diets can still be used to
increase n-3 HUFA in fish body oils at a point where the fish has undergone most
of its growth increment but has not yet reached the reproductive phase.
A final reason for seeking substitutes for FM and FO relates to the levels of POPs
present in some geographical sources of marine raw materials. It is generally established that the lowest levels of contaminants are found in pelagic fish species from
South America, while the highest levels are found in those caught in Northern Europe
(Easton et al. 2002; FIN 2004). In addition, due to tightening of EU legislation in
2001, a significant proportion of Northern European FO and FM, particularly some
of those originating from the Baltic and Barent seas, would no longer be eligible for
inclusion in animal and aquafeeds (SCAN 2000; FIN 2004; EC, 2006b).
6.3 Fish Oil and Fish Meal Substitution
6.3.1 Effects of Fish Oil Replacement on Growth Performance
Over the last five years a large number of studies have investigated a range of FO
substitutes in a wide range of species. However, all of these earlier studies fed the
experimental diets for only a small part of the growth cycle for each species, usually
only for 8–20 weeks. By contrast, the studies undertaken as part of the EU project,
RAFOA, were unique in that they were long term trials from juvenile stages or
covered the whole cycle from first feeding to harvest (www.rafoa.stir.ac.uk).
In salmon smolts, replacement of FO with increasing quantities (25–100%) of linseed oil (LO), rapeseed oil (RO) and olive oil (OO) had no effect on growth or survival
(Torstensen et al. 2004a; Bell et al. 2004a) and confirms reports of similar studies using
either low (Hardy et al. 1987; Bell et al. 1991; Waagbø et al. 1991, 1993) or high
energy diets in Atlantic salmon (Bell et al. 2001a, 2002; Rosenlund et al. 2001;
Torstensen et al. 2000, 2004b). These studies show similar growth responses to other
189
fish species that could be used directly as food for humans, in animal feeds (Tacon
1997; Goldburg and Naylor 2005). Furthermore, there is also heightened public and
non-governmental organisations (NGO) awareness over the management of feed
grade fisheries and the potential impact on marine ecosystems particularly effects
on sea birds and marine mammals (Huntington et al. 2004).
A further reason to substitute FO for VO in fish diets is that carnivorous fish
have evolved to use oil for the energy required to fuel growth and reproduction.
Thus, in effect, most of the oil consumed by fish is effectively “burned” to supply
energy and fish do not seem to discriminate greatly between which fatty acids are
retained and which are metabolised. Therefore, once essential fatty acid requirements
have been met the excess n-3 PUFA in FO are stored as triacylglycerols in body
stores and then used for energy production (Sargent et al. 2002). For that reason, it
might be more productive to feed VO for energy production, in place of FO, for
most of the production cycle and not waste valuable n-3 HUFA in the production
of energy for growth. Further, the use of FO finishing diets can still be used to
increase n-3 HUFA in fish body oils at a point where the fish has undergone most
of its growth increment but has not yet reached the reproductive phase.
A final reason for seeking substitutes for FM and FO relates to the levels of POPs
present in some geographical sources of marine raw materials. It is generally established that the lowest levels of contaminants are found in pelagic fish species from
South America, while the highest levels are found in those caught in Northern Europe
(Easton et al. 2002; FIN 2004). In addition, due to tightening of EU legislation in
2001, a significant proportion of Northern European FO and FM, particularly some
of those originating from the Baltic and Barent seas, would no longer be eligible for
inclusion in animal and aquafeeds (SCAN 2000; FIN 2004; EC, 2006b).
6.3 Fish Oil and Fish Meal Substitution
6.3.1 Effects of Fish Oil Replacement on Growth Performance
Over the last five years a large number of studies have investigated a range of FO
substitutes in a wide range of species. However, all of these earlier studies fed the
experimental diets for only a small part of the growth cycle for each species, usually
only for 8–20 weeks. By contrast, the studies undertaken as part of the EU project,
RAFOA, were unique in that they were long term trials from juvenile stages or
covered the whole cycle from first feeding to harvest (www.rafoa.stir.ac.uk).
In salmon smolts, replacement of FO with increasing quantities (25–100%) of linseed oil (LO), rapeseed oil (RO) and olive oil (OO) had no effect on growth or survival
(Torstensen et al. 2004a; Bell et al. 2004a) and confirms reports of similar studies using
either low (Hardy et al. 1987; Bell et al. 1991; Waagbø et al. 1991, 1993) or high
energy diets in Atlantic salmon (Bell et al. 2001a, 2002; Rosenlund et al. 2001;
Torstensen et al. 2000, 2004b). These studies show similar growth responses to other