In 1951 Dr John E Halver of the School of Fisheries Science, University of Washington, USA presented the ‘model semi-purified fish diet’ to the aquatic nutrition research community. This innovation allowed for the proliferation of deficiency studies with mainly salmonid fish such as rainbow trout and Pacific salmon to evaluate the significance of vitamins in complete diets for cultured fish.
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3. I
n 1951 Dr John E Halver of the
School of Fisheries Science, University
of Washington, USA presented the
‘model semi-purified fish diet’ to the
aquatic nutrition research community. This
innovation allowed for the proliferation of
deficiency studies with mainly salmonid fish
such as rainbow trout and Pacific salmon
to evaluate the significance of vitamins in
complete diets for cultured fish.
With such an ‘ideal’ diet, vitamins could
easily be assayed by using this vitamin test
diet, consisting of ‘vitamin free’ carbohydrate
and protein sources i.e. casein, purified gelatin,
potato starch, hydrogenated cotton seed oil,
alpha-cellulose flour, minerals, cod liver oil,
combined with crystalline vitamins. Each vita-
min could then be systematically assessed by
selective exclusion from this advanced basal
diet formulation. The water soluble vitamins
such as the B-complex and especially vitamin
C (ascorbate) were all found to be essential
in fish as in other terrestrial animals of com-
mercial importance and indeed having the
same basic functions as in humans.
The role of niacin (vitamin B3) is no
less important within aquatic species; as fish
farming became more prevalent, the health
status of stocks fluctu-
ated due to the wide
spectrum of feed for-
mulations at that time.
A number of nega-
tive symptoms were
attributed to niacin
deficiency and steps
were taken to protect
against them based on
early evidence.
In the 1940s and
1950s fish were found
to have a loss of appetite and poor food
conversion (food intake to body weight ratio)
that progressed into a darker skin colour,
anorexia, posterior gut lesions, oedema of
the stomach and intestine, erratic motion and
at-rest muscle spasms. In the late 1950s and
1960s, a predilection to sunburn in fish was
discovered and, in carp, subcutaneous haem-
orrhages developed under chronic and acute
niacin deficiency.
In the 1970s, eels were found to develop
skin lesions and display erratic swimming,
while lesions, deformed jaws, and anaemia
were discovered in catfish, Ictalarus punctatus.
The period from 1980 to date encompassed
a series of investigations that augments earlier
knowledge, but there have been relatively few
studies in the early 21st century except for the
work of Shaik Mohammed et al. (2001) where
pathological effects of niacin deficiency similar
to this described above were reported from
studies with Indian catfish (Heteropneustes
fossilis).
Metabolic considerations
Exogenous proteins within the diet supply
the metabolic pool with essential and non-
essential amino acids. Among these is tryp-
tophan which has considerable importance in
fish nutrition. In mammals, there is a recog-
nised and documented conversion pathway
from tryptophan to niacin, thus allowing tryp-
tophan, and proteins rich in tryptophan, to be
an important reservoir for niacin biosynthesis.
Although the essential amino acid tryp-
tophan is a precursor of niacin, this endog-
enous synthesis, comprising 13 steps in a
metabolic sequence is not deemed efficient.
Studies in man have shown that approximately
60 mg of tryptophan are required to produce
1 mg of niacin and this ratio varies consider-
ably within different vertebrate groups.
Fish, however, may even lack this conver-
sion capacity or have very a poor efficacy for
this metabolic pathway. By supplementing
both a niacin deficient and niacin complete
diet with varying amounts of tryptophan, it
was previously determined that tryptophan
levels have no effect on niacin accumulation.
Serrano and Nagayama (1991) found that the
3-hydroxyanthranilic acid (3-HAA) to picolinic
acid carbolase (PC) activity ratio in rainbow
trout suggested an ineffective conversion from
tryptophan to niacin. This finding will help
explain higher niacin requirements for some
fish, as others do carry the capacity in some
degree but this cannot be an insurance against
providing a separate dietary supply. Niacin
and niacinamide
are required by
all living cells
and their chemi-
cal structure
is depicted in
Figure 1.
They are
essential com-
ponents of two
coenzymes,
niacinamide
adenine dinucle-
Niacin: one of the key B
vitamins for sustaining healthy
fish growth and production
by Simon J Davies and Mark Rawling, Aquaculture Nutrition & Health Group, Plymouth
University, United Kingdom
Nicotinic Acid Nicotinamide
Figure 1: Niacin in its two biologically active forms as presented to fish for assimilation
20 | InternatIonal AquAFeed | May-June 2013
FEATURE
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6. carbohydrate. In general, certain warm
water fish, namely carnivorous species, uti-
lise dietary carbohydrate poorly and it
is recognised that carbohydrate obtained
from different sources may not be equally
available to all fish of the same species.
There is merit for consideration of the
changes in protein level, quality, and protein
to energy ratio for optimum vitamin levels
to be recommended. Modern fish diets are
much higher in energy, presented as oil for
carnivorous fish, whilst carbohydrate in the
form of starch is quite acceptable for omni-
vores such as tilapia and carp. Niacin is given
special importance in this area due to its
relevancy in the metabolism of protein and
the release of energy from these nutrients
as stated previously.
However implications towards dietary
requirement and variability, warrants a need
to establish additional scientific information
regarding the digestibility of niacin and sub-
sequent availability coefficients within varying
diets formulations based on practical ingre-
dients.
From the data of Ng et al. (1998), it was
suggested that niacin supplementation can be
reduced to a more efficient level due to the
relatively high amount of biologically available
niacin found in typical feed ingredients used
in modern fish feed formulations. However,
the provisions may not be adequate to
meet current safety margins to guarantee
production and health criteria for all spe-
cies. Also, the inability to utilise particular
fish feeds due to varying dietary constraints
would justify continued supplementation and
refinement. In addition, it was found that the
bioavailability of niacin increased by some
57 percent when corn meal was extrusion
cooked rather than administered in the
diet in its native form. This suggests that
processing technology is an important area
for further investigation for determining the
optimum inclusion levels of niacin for a range
of aquatic species.
Stability and processing losses
Niacin is regarded as a highly stable vitamin
in animal nutrition and is usually added to
feed as nicotinic acid or nicotinamide within
the vitamin premix formulations within a dry
mixture with a carrier material along with
other vitamins and possibly mineral supple-
ments as well.
The advent of high energy and nutrient
dense feeds in many countries engaged in
intensive fish farming operations has also
placed a higher burden on maintaining the
health of fish, whilst promoting faster growth
rates and efficient feed utilisation. The use
of expanded and extruded feeds offer more
scope in feeding management but may greatly
influence the levels of vitamins available to
fish under various conditions. Extrusion of
diets has the tendency to reduce the activity
of vitamins especially those within the water
soluble class and the processing of raw materi-
als may lead to serious losses. Generally this is
in the order of 10-20 percent for most vita-
mins reported (Tacon, 1985, Gabaudan and
Hardy, 2000). Further reductions are caused
by storage of pelleted feed and this may result
in impairment to fish health and production
efficiency over extended time.
Future perspective
Indeed, the movement towards new fish
species in aquaculture such as flounders;
turbot, sole and halibut as well as sea bass
and sea bream in Europe, cobia in the
USA and Brazil have generated considerable
interest in producing specific diets that can
meet their individual requirements for growth,
development and health. Much is known
about the gross nutritional requirements of
these emerging species but little on vitamins,
especially niacin. Intensive rearing conditions
(i.e. UV light exposure to outdoor pens)
and husbandry related factors may adversely
affect the physiological status of fish and
induce metabolic stress causing tissue dam-
age and impaired performance. The potential
of niacin supplementation in reducing such
effects could prove a valuable area for future
investigation.
22 | InternatIonal AquAFeed | May-June 2013
FEATURE
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They are what they eat
Enhancing the nutritional value of live feeds
with microalgae
Controlling mycotoxins with
binders
Ultraviolet
water disinfection for fish
farms and hatcheries
Niacin
– one of the key B vitamins for sustaining
healthy fish growth and production
Volume 16 Issue 3 2013 - mAY | Ju Ne
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