World Aquaculture - December 2014

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• WORLD AQUACULTURE • DECEMBER 2014 37
of the issue is growing among
nutritionists, two inevitable
developments might aggravate
the risk of inflammatory
disorders in cultured fish.
Raw material availability.
Diets rich in fish oil have strong
anti-inflammatory properties
but these benefits are less likely
to be found in future aquafeeds.
Enabling further double-digit
growth rates of aquaculture
will require ongoing reductions
in the incorporation of fish oil
in aquafeed formulation, as
has already been observed in
recent years (Fig. 2). Fish oil is
mainly produced from small
pelagic fish species and the
global capture of these species
has increased 7-fold since the
1950s but has stabilized at
approximately 20-25 million
t within the last two decades.
Future increases in aquaculture
production will evidently
require efficient replacement of
fish oil, if high-energy diets with
current lipid contents of up to 40
percent in salmonid feeds are to
be produced (Pettersson 2010).
Fish oil is an excellent
source of polyunsaturated
fatty acids (PUFA), key
substances that reduce intestinal
inflammation. Although
substitution by vegetable oils
might improve the bottleneck
of oil availability and generate benefits in aquaculture sustainability,
the fatty acid concentrations of both oil sources are different. Many
oils of plant origin are rich in linoleic acid (18:2n-6), oleic acid
(18:1n-9) and partially α-linoleic acid (18:3n-3). However, they lack
the highly unsaturated fatty acids (HUFA), fatty acids with ≥ 20 C20
and ≥ 3 double bonds (Sargent et al. 1989).
Breeding and improved genetics. Enhanced growth performance
is linked to increased metabolic formation of reactive oxygen
compounds that can induce oxidative stress and lead to the devel-
opment of chronic inflammation. Compared to many land-based
livestock, a number of the most important cultured aquatic species
have been domesticated during the last decades or only relatively
recently included in breeding programs. Atlantic salmon breeders
can already look back on some decades of successful work, with a
gradual inclusion of functional traits, such as disease resistance (fu-
runculosis, infectious salmon anaemia), fat content and fat distribu-
tion or body shape. Further genetic improvement with higher growth
performance or feed efficiency can be expected for most cultured
aquatic species (Gjøen and Bentsen 1997, Ponzoni et al. 2008).
The electron transport
chain, a central part of the
process of making dietary
energy available to the
organism, is an important
source of free radicals, such
as reactive oxygen. Increases
in energy metabolism,
resulting in faster growth
rates, are closely related to an
elevated production of these
reactive oxidants, which will
increase the development of
inflammatory effects.
Potential of
Anti-inflammatory
Additives
One promising
approach to controlling the
frequent chronic form of
inflammation—and thus
to improving nutrition,
performance and health of
fish—is the inclusion of special
plant-derived ingredients with
strong anti-inflammatory
properties in diets of animals.
Although future research
must close some gaps in
knowledge, such as absorption
and bioavailability of the
substances, a growing number
of in vitro and in vivo trials
have shown the benefits of such
additives.
Flavonoids, secondary
plant metabolites found in
nearly all higher plants, are an interesting group of naturally active
substances. The compounds consist of two aromatic and one
heterocyclic ring and can be divided in different sub-classes wherein
flavan derivatives exhibit strong anti-inflammatory properties (Fig.
3). The sub-classes differ in the functional group of the ring system.
The main effect of flavonoids is an inhibition of the activation of
the protein complex NF-ĸB, which is considered a central regulator
of inflammation at the cellular level. Other mechanisms might
contribute to the amelioration of inflammatory actions, inasmuch
as flavonoids also are related to a reduced metabolic production
of reactive oxidants. Flavonoids have good processing properties
because they are relatively heat stable during practical aquafeed
manufacturing (Wuerzbach et al. 2014).
The anti-inflammatory effects of flavonoids have been
demonstrated repeatedly in studies investigating a variety of samples,
such as immune, blood or intestinal cells (Gonzales et al. 2011).
So far, most information is available on the benefits of flavonoids
derived from green tea and red grapes (Fig. 4) and most flavonoid
TOP, FIGURE 3. Sub-groups of polyphenols. MIDDLE, FIGURE 4. Red grapes,
a good source of flavonoids (Photos: Susanne Kirwan). BOTTOM, FIGURE 5.
Sturgeon used for commercial caviar production (Photos: Susanne Kirwan).
( C O N T I N U E D O N P A G E 3 8 )