1. Oceanography Department, Faculty of Science, Alexandria University, Alexandria, Egypt
This study was conducted to evaluate the effects of dietary
taurine on growth performance and feed utilization of
Nile tilapia (Oreochromis niloticus) larvae. Four plant
protein-based, isonitrogenous (400 g kgÀ1
protein), isoener-
getic (19 MJ kgÀ1
) diets supplemented with four taurine
concentrations (0.0, 5.0, 10.0 and 15.0 g kgÀ1
; designated
as T0, T0.5, T1 and T1.5, respectively) were prepared. The
diets were fed to triplicate groups of fish larvae (0.024 g
average body weight), to apparent satiation, three times
per day for 60 days. Larval growth rates and feed utiliza-
tion efficiency were significantly improved with increasing
supplemental taurine up to 10 g kgÀ1
and decreased with
further taurine supplementation. The quadratic regression
analyses indicated that the maximum larval performance
occurred at about 9.7 g kgÀ1
of total dietary taurine. Fish
survival was significantly lower at 15 g kgÀ1
dietary taurine
than at other taurine levels. Body protein significantly
increased, while body moisture and ash decreased, with
increasing dietary taurine up to 10 g kgÀ1
and decreased
with further taurine supplementation to 15 g kgÀ1
. Body
lipid was not significantly affected by dietary taurine con-
centration. A number of body amino acids (tryptophan,
arginine, histidine, leucine, isoleucine, valine, alanine, gly-
cine, threonine and taurine) significantly increased with
increasing supplemental taurine up to 10 g kgÀ1
and then
decreased with further increase in dietary taurine levels.
The rest of body amino acids were not significantly affected
by dietary taurine. The present results suggest that about
9.7 g kgÀ1
dietary taurine is required for optimum perfor-
mance of Nile tilapia larvae fed soybean meal-based diets.
KEY WORDS: feed utilization, growth, larvae, Nile tilapia,
soybean meal, taurine
Received 9 July 2014; accepted 22 October 2014
Correspondence: A.-F.M. El-Sayed, Oceanography Department, Faculty
of Science, Alexandria University, Moharram Bey 21511, Alexandria,
Egypt.
E-mail: abdelfatah.youssif@alexu.edu.eg
Tilapia culture has grown rapidly during the past two dec-
ades, so that tilapias are currently the second largest
farmed finfish group in the world, only after carps (FAO
2014). This rapid industrialization of tilapia production in
recent years has led to gradual shift in tilapia culture from
extensive and semi-intensive systems to more intensive
farming practices, with an increasing demand for quality
seeds and dependence on formulated feeds (El-Sayed 2006).
Therefore, the production of sufficient quantities of high-
quality seeds and the formulation of appropriate, cost-
effective feeds have become a major challenge facing tilapia
culture industry. This means that the profitability of tilapia
culture is directly related to the quality of the seeds used
and the quantity and quality of feed consumed by the fish.
The shortage of quality tilapia seed production to meet the
increasing farmers’ demand remains one of the major chal-
lenges facing the expansion of tilapia culture (El-Sayed 2006).
Therefore, considerable attention has been paid to larval rear-
ing and nutrition of farmed tilapia during the past two dec-
ades. Similarly, the nutrient requirements and feeding
management of tilapia broodstock have been extensively stud-
ied (Gunasekera et al. 1996a,b; Gunasekera & Lam 1997;
El-Sayed et al. 2003, 2005; El-Sayed & Kawanna 2008).
The increasing demand for fish meal (FM) accompanied
by shortage in global supply has resulted in escalating FM
prices during the past few years (Tacon et al. 2012). There-
fore, intensive efforts have been given to the replacement
of FM with less costly and more available plant protein
sources for aquaculture feed production. In this regard,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ª 2015 John Wiley & Sons Ltd
2015 doi: 10.1111/anu.12266. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aquaculture Nutrition

2. particular attention has been given to oil plant sources,
such as soybean meal (SBM), cotton seed meal, sunflower
meal and sesame seed meal, as a partial or total fishmeal
replacer in aquafeed industry (Tacon et al. 2011). Despite
that these sources have good protein contents and essential
amino acid (EAA) profiles, they are limited in a number of
EAAs, such as sulphur-containing amino acids (methionine
and cysteine) and lysine. They also contain many endoge-
nous antinutrients including protease inhibitors, phytohae-
magglutinin and antivitamins, which may negatively affect
their nutritional values (El-Sayed 2006).
Most of the ingredients of plant origin are also limited in
taurine (2-aminoethanesulfonic acid) which is an end prod-
uct of metabolism of sulphur-containing amino acids. Tau-
rine is often classified as amino acid, despite that it lacks a
carboxyl group. It is not also incorporated into protein
synthesis or degradation of mammalian tissues (Kuzmina
et al. 2010). However, taurine accounts for 30–50% of the
entire amino acid pool, depending on the animal species
(Jacobsen & Smith 1968). Taurine is involved in many
physiological functions in mammals, including modulation
of immune response, calcium transport (Takahashi et al.
1992), retina development (Omura & Yoshimura 1999), bile
acid metabolism (Hofmann & Small 1967), osmotic regula-
tion (Thurston et al. 1980) and endocrine functions (Kuz-
mina et al. 2010). It also plays an important role in the
development of both muscular and neural systems. Full
details of taurine synthesis and functions in fish and shrimp
are reviewed by El-Sayed (2014).
Taurine synthesis in fish varies widely among fish species,
depending on fish species and developmental stage, feeding
habits and feeding histories and the water environment in
which the fish lives. This could also be related to the varia-
tion in the activity of L-cysteinesulfinate decarboxylase
(CSD), which is a key enzyme for the oxidation and direct
conversion of cysteine to taurine or conversion of methio-
nine into cysteine, mainly in the liver and brain (Jacobsen
& Smith 1968; Chang et al. 2013).
Although taurine is a non-essential nutrient, its inclu-
sion in the diet could improve fish performance. For
example, marine fish species, such as Japanese flounder
(Paralichthys olivaceus), Red sea bream (Pagrus major)
and yellowtail (Seriola quinqueradiata), lack, or have low
ability of taurine synthesis due to the absence of or lim-
ited CSD activities (Goto et al. 2001; Yokoyama et al.
2001; Park et al. 2002; Takagi et al. 2005, 2008, 2011;
Kim et al. 2008). Dietary taurine supplementation may be
indispensible for these fishes, particularly if they are fed
plant-based diets.
On the other hand, studies on taurine synthesis and
physiological functions in freshwater fishes are contradic-
tory. Some freshwater fishes, such as common carp, rain-
bow trout and Atlantic salmon, have been reported to
have the ability to synthesize taurine; thus, they may not
require exogenous supplemental taurine (Goto et al. 2001;
Yokoyama et al. 2001; Espe et al. 2008, 2012). In contrast,
taurine supplementation has been found essential for opti-
mal performance of freshwater fish such as rainbow trout
(Gaylord et al. 2006, 2007), grass carp (Ctenopharymgodon
idellus) (Luo et al. 2006) and Nile tilapia (Goncßalves et al.
2011). It is evident that taurine is conditionally essential
when these fishes are fed diets of plant origin and deficient
in methionine and/or cysteine. The essentiality of taurine
for freshwater fishes may also be affected by the feeding
habits and previous feeding histories of these fishes
(Gaylord et al. 2006).
The effects of dietary taurine supplementation on the
performance and biological functions of Nile tilapia
(Oreochromis niloticus) are not well understood. As far the
authors know, only one study investigated the response of
Nile tilapia larvae fed plant protein diets to supplemental
taurine (Goncßalves et al. 2011). The preliminary results of
that study revealed that the larvae require 8 g kgÀ1
taurine
for optimum performance. However, the taurine range used
in that study was relatively narrow (2–8 g kgÀ1
); and there-
fore, it is not known whether Nile tilapia larvae would
require higher dietary taurine levels. It is evident that more
research is urgently needed to study the effects of wider
exogenous taurine levels on the growth performance and
feed efficiency of different sizes and growth stages of Nile
tilapia fed protein sources of plant origins.
Therefore, this study was carried out at Oceanography
Department, Faculty of Science, Alexandria University,
Egypt, to investigate the effects of dietary taurine on growth,
feed efficiency, body composition and amino acid profiles of
Nile tilapia (O. niloticus) larvae fed soybean-based diets.
Newly hatched Nile tilapia (O. niloticus) larvae were
obtained from a private hatchery near Alexandria, Egypt.
The fish were stocked in a 1-m3
fibreglass tank filled with
dechlorinated tap water for 24 h for resting. Triplicate
groups of 200 larvae (0.024 g average weight) were stocked
in 140-L glass aquaria connected in a closed, recirculating
system containing a biological filter. The culture system
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Aquaculture Nutrition ª 2015 John Wiley & Sons Ltd

3. was also provided with continuous aeration using an air
compressor (BOYU; Boyu industries Co., Ltd., North City
Industrial Village, Raoping, China). Water temperature
was maintained at 27 Æ 1 °C, while natural light was used
throughout the study. Faeces were siphoned each morning,
before the first feeding and about 10% of the water was
replaced with fresh dechlorinated water of the same tem-
perature. Water quality parameters including dissolved oxy-
gen (DO), ammonia (NH4–N), nitrates (NO3–N), nitrites
(NO2–N) and pH were examined twice a week using
HACH test kit (Loveland, CO, USA). The average values
of these parameters throughout the study were as follows:
DO = 5.7 Æ 1.2 mg LÀ1
, pH = 7.8 Æ 0.10, NH4–
N = 0.081 Æ 0.002 mg LÀ1
, NO3–N = 0.72 Æ 1.61 mg LÀ1
and NO2–N = 0.00 mg LÀ1
.
Four SBM-based, isonitrogenous (400 g kgÀ1
cp), isoener-
getic (19 MJ kgÀ1
) diets were prepared, containing four
concentrations of taurine (0.0, 5.0, 10.0 and 15.0 g kgÀ1
;
designated as T0, T0.5, T1 and T1.5, respectively). In fact,
when we started this series of experiments on taurine
requirement of Nile tilapia, we used five levels (0.0, 5.0,
10.0, 15.0 and 20.0 g kgÀ1
) fed to fingerling fish (1.0 g).
We found that beyond 10.0 dietary taurine, the perfor-
mance and survival of the fish were reduced substantially
(data are being processed for publication). Therefore, we
decided to reduce the inclusion levels to four (0.0, 5.0, 10.0
and 15.0 g kgÀ1
) for broodstock study and larval study.
The composition and proximate analysis and amino acid
profiles of the diets are shown in Tables 1 & 2. The diets
were prepared as described by El-Sayed et al. (2013). The
fish were fed the test diets to apparent satiation, three times
per day (at 09.00, 13.00 and 17.00 h), for 60 days. The fish
in each aquarium were collected and weighed at 15-day
intervals, and the average weights were recorded. The
amounts of feed consumed by fish in each aquarium during
each feeding interval were also recorded.
At the termination of the study, all fish in each aquarium
were netted, counted, weighed to the nearest mg and stored
at À20 °C for final body composition and amino acid
analyses. Initial body analyses were performed on a pooled
sample of fish, which was weighed and frozen before the
study. A sample of each test diet was also stored at
À20 °C for chemical analysis. Proximate analysis of mois-
ture, protein, lipid and ash was performed according to
Table 1 Composition and proximate analysis (g kgÀ1
dry weight) of the test diets
Ingredients
Experimental diets
T0 T0.5 T1 T1.5
Fish meal 100 100 100 100
Soybean meal 700 700 700 700
Wheat bran 110 105 100 95
Taurine 0.0 5 10 15
Soybean oil 20 20 20 20
Fish oil 20 20 20 20
Vitamins and minerals mix1
20 20 20 20
Dicalcium phosphate 20 20 20 20
Binder (CMC)2
10 10 10 10
Total 1000 1000 1000 1000
Crude protein 404.0 396.1 398.8 392.9
Ether extract 81.0 79.3 82.1 75.5
Crude fibre 31.3 28.0 35.0 30.0
Ash 141.0 134.0 128.0 130.0
NFE3
342.7 362.6 356.1 371.6
Taurine 0.9 7.0 11.0 16.5
GE4
18.78 18.87 18.93 18.80
1
Vitamins & minerals mixture contains mg kgÀ1
or IU kgÀ1
of dry vitamins & minerals powder: Vit. A 2 200 000 IU., Vit. D3 1 100 000
I.U., Vit. E 1500 I.U., Vit. K 800 mg, Vit. B1 1100 mg, Vit. B2 200 mg, Vit. B6 2000 mg, Vit. H 15 mg, Vit. B12 4 mg, Vit. C 3000 mg, Iron
160 mg, Magnesium 334 mg, Copper 21.6 mg, Zink 21.6 mg, Selenium 25 mg, Cobalt 2.38 mg.
2
Carboxymethyl cellulose used as binder.
3
Nitrogen-free extract determined by difference.
4
Gross energy calculated based on 23.64, 39.54 and 17.57 KJ gÀ1
for protein, lipid and carbohydrate, respectively.
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Aquaculture Nutrition ª 2015 John Wiley & Sons Ltd

4. standard AOAC (1995) methods. Amino acids profiles in
the diets and in the whole fish body (freeze dried) were
determined using an automated amino acid analyzer (Hit-
achi L-8500A; Hitachi, Ibaraki, Japan), as described by
Kim et al. (2005).
Growth rates and feed efficiency were calculated as follows:
Percentage weight gain (PWG) ¼ 100 ðWf À WiÞ=Wi;
Specific growth rate ð% SGRÞ ¼ 100 ðln Wf À ln WiÞ=t;
where Wi and Wf are initial and final weights (g), and t is
the time of experiment (days).
Feed conversion ratio (FCR) ¼ dry feed intake (g)=
fish live weight gain (g):
Protein productive value (PPV) ¼ 100 ðprotein gain (g)Þ=
protein fed (g) on dry weight basis
.
Simple linear and nonlinear regressions were performed to
correlate the relationships between fish performance and die-
tary taurine concentrations. Nonlinear and linear functions
were estimated by the least square method using the SPSS
program, version 12 (SPSS Inc., Chicago, IL, USA). All data
were also subjected to a one-way analysis of variance
(ANOVA) at a 95% confidence limit, using SPSS software.
Duncan’s multiple range test was used to compare means
when F-values from the ANOVA were significant (P < 0.05).
The present results showed that supplementation of dietary
taurine significantly affected (P < 0.05) the growth rates and
feed utilization efficiency of Nile tilapia larvae (Table 3).
Larval growth rates and feed utilization efficiency were sig-
nificantly improved (P < 0.05) with increasing supplemental
taurine up to 10 g kgÀ1
and decreased with further taurine
supplementation. The quadratic regression analyses indi-
cated that the maximum larval performance occurred at
9.7 g kgÀ1
of total dietary taurine. The equations represent-
ing the relationships between fish performance (y) and die-
tary taurine (x) were as follows:
PWG : y ¼ À36:261x2
þ 707:82x þ 4001:9; R2
¼ 0:7887
SGR : y ¼ À0:0095x2
þ 0:1836x þ 6:3169; R2
¼ 0:8215
FCR : y ¼ 0:0049x2
þ 0:0947x þ 1:5949; R2
¼ 0:7825
Larval survival was not significantly affected by taurine
supplementation up to 10 kgÀ1
(P > 0.05). Increasing
Table 2 Amino acid content (% dry weight) of the test diets
Amino acid
Experimental diets
T0 T0.5 T1 T1.5
Lysine 2.27 2.31 2.26 2.17
Methionine 0.54 0.55 0.54 0.51
Threonine 1.25 1.26 1.25 1.20
Tryptophan 0.58 0.61 0.60 0.58
Arginine 3.01 2.87 2.94 3.00
Phenylalanine 1.56 1.42 1.66 1.58
Histidine 0.98 0.98 0.95 1.02
Isoleucine 1.15 1.22 1.16 1.21
Leucine 2.32 2.51 2.38 2.44
Valine 2.13 2.10 2.21 1.99
Cysteine 0.41 0.35 0.39 0.42
Alanine 2.00 2.14 2.01 1.96
Glutamic acid 6.86 6.69 6.58 6.62
Glycine 1.51 1.44 1.40 1.39
Serine 1.62 1.58 1.56 1.60
Aspartic acid 3.68 3.38 3.43 3.52
Proline 2.42 2.41 2.39 2.27
Taurine 0.09 0.70 1.10 1.65
Table 3 Effects of dietary taurine supplementation on growth rates, feed utilization and survival (mean Æ SEM) of Nile tilapia fry
Growth parameter
Experimental diets
T0 T0.5 T1 T1.5
Initial weight (g fishÀ1
) 0.024 0.024 0.024 0.024
Final weight (g fishÀ1
) 1.18 Æ 0.011d
1.61 Æ 0.02b
1.94 Æ 0.08a
1.46 Æ 0.03c
Percentage weight gain 4817 Æ 48d
6608 Æ 87b
7997 Æ 337a
5983 Æ 127c
Specific growth rate 6.49 Æ 0.02d
7.01 Æ 0.02b
7.32 Æ 0.07a
6.84 Æ 0.04c
Feed consumed (g fishÀ1
) 1.82 Æ 0.087b 2.44 Æ 0.050a 2.68 Æ 0.017a 2.43 Æ 0.044a
Feed conversion ratio 1.57 Æ 0.05b
1.54 Æ 0.05b
1.40 Æ 0.07a
1.69 Æ 0.02c
Protein productive value 23.32 Æ 0.85c
27.39 Æ 1.24b
35.55 Æ 2.24a
26.22 Æ 0.22b
Survival (%) 84.50 Æ 0.29a
86.33 Æ 4.06a
85.33 Æ 2.33a
75.34 Æ 1.45b
Values in the same row with different letters are significantly different at P = 0.05.
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Aquaculture Nutrition ª 2015 John Wiley & Sons Ltd

5. supplemental taurine to 15 kgÀ1
resulted in a sharp reduc-
tion in fish survival (P < 0.05).
Body composition of Nile tilapia larvae was significantly
affected (P < 0.05) by dietary taurine supplementation
(Table 4). Body moisture and ash decreased with increasing
dietary taurine up to 10 kgÀ1
and increased afterwards.
Body protein significantly increased with increasing dietary
taurine up to 10 kgÀ1
and levelled off with further taurine
supplementation to 15 kgÀ1
. Body lipid was also signifi-
cantly increased with increasing supplemental taurine up to
10 kgÀ1
and decreased with further taurine supplementa-
tion to 15 kgÀ1
.
The following body amino acids (tryptophan, arginine,
histidine, leucine, isoleucine, threonine, valine, alanine, gly-
cine and taurine) significantly increased (P < 0.05) with
increasing supplemental taurine up to 10 g kgÀ1
and then
decreased, or levelled off (leucine and taurine) with further
increase in taurine levels (Table 5). On the other hand,
other amino acids (lysine, methionine, phenylalanine, cyste-
ine, glutamic acid, serine, aspartic acid and proline) were
not significantly affected by dietary taurine (P > 0.05).
Generally, marine fish and shrimp larvae lack the ability to
synthesize taurine from methionine through cysteinesulfi-
nate decarboxylase (CSD) pathway (Brotons-Martinez
et al. 2004; Mayasari 2005). Therefore, they have been
reported to require exogenous taurine supplementation for
maximum development, growth, feed utilization and sur-
vival. For example, enriching live food such as Artemia
and rotifers with taurine improved morphology, develop-
ment and performance of marine fish larvae (Salze et al.
2011; Yun et al. 2012). When larval red sea bream
(P. major) (Chen et al. 2004), European sea bass (Dicen-
trarchus labrax) (Brotons-Martinez et al. 2004), Japanese
Table 4 Body composition (g kgÀ1
) (mean Æ SEM) on wet weight basis of Nile tilapia larvae fed the test diets
Composition (g kgÀ1
) Initial
Experimental diets
T0 T0.5 T1 T1.5
Moisture 692.00 740.22 Æ 2.82a
729.41 Æ 2.37a
683.13 Æ 3.3b
703.20 Æ 1.56c
Protein 187.89 147.82 Æ 1.72a
166.00 Æ 0.25b
168.91 Æ 0.38c
168.07 Æ 1.23c
Lipid 40.69 44.85 Æ 0.36a
51.11 Æ 1.19b
58.24 Æ 1.96c
54.69 Æ 1.86d
Ash 85.62 66.35 Æ 0.26b
60.87 Æ 1.58a
66.73 Æ 2.94b
72.21 Æ 0.98c
Values in the same row with different letters are significantly different at P = 0.05.
Table 5 Amino acid profiles in whole body (mean Æ SEM) (% dry weight) of Nile tilapia fry fed the test diets
Body amino acid
Experimental diets
T0 T0.5 T1 T1.5
Lysine 3.66 Æ 0.04a
3.71 Æ 0.01a
3.90 Æ 0.02a
3.63 Æ 0.16a
Methionine 1.47 Æ 0.012a
1.42 Æ 0.08a
1.37 Æ 0.13a
1.42 Æ 0.09a
Threonine 1.87 Æ 0.08b
2.19 Æ 0.005a
2.31 Æ 0.01a
1.91 Æ 0.05b
Tryptophan 0.54 Æ 0.003d
0.60 Æ 0.005b
0.65 Æ 0.007a
0.58 Æ 0.001c
Arginine 2.46 Æ 0.05c
2.79 Æ 0.09b
3.09 Æ 0.016a
2.60 Æ 0.04bc
Phenylalanine 1.79 Æ 0.11a
1.79 Æ 0.066a
1.90 Æ 0.05a
1.83 Æ 0.019a
Histidine 1.22 Æ 0.017d
1.59 Æ 0.035b
1.74 Æ 0.040a
1.29 Æ 0.004c
Isoleucine 2.64 Æ 0.011b
2.67 Æ 0.02b
2.85 Æ 0.051a
2.70 Æ 0.004b
Leucine 3.29 Æ 0.02b
3.52 Æ 0.035a
3.72 Æ 0.013a
3.59 Æ 0.13a
Valine 2.43 Æ 0.08b
2.71 Æ 0.11ab
2.85 Æ 0.027a
2.65 Æ 0.05ab
Cysteine 0.77 Æ 0.011a
0.72 Æ 0.026a
0.74 Æ 0.004a
0.78 Æ 0.032a
Alanine 2.93 Æ 0.02b
2.95 Æ 0.035b
3.16 Æ 0.05a 2.91 Æ 0.048b
Glutamic acid 6.57 Æ 0.34a
6.91 Æ 0.29a
6.79 Æ 0.76a
6.32 Æ 0.11a
Glycine 2.60 Æ 0.02c
2.73 Æ 0.025b
2.87 Æ 0.045a
2.66 Æ 0.015bc
Serine 1.74 Æ 0.07a
1.57 Æ 0.005a
1.71 Æ 0.02a
1.76 Æ 0.22a
Aspartic acid 5.58 Æ 0.25a
4.98 Æ 0.17a
4.93 Æ 0.03a
5.06 Æ 0.18a
Proline 3.10 Æ 0.20a
2.69 Æ 0.16a
2.82 Æ 0.065a
3.05 Æ 0.19a
Taurine 0.13 Æ 0.003c
0.74 Æ 0.04b
1.09 Æ 0.09a
1.15 Æ 0.06a
Total 44.83 Æ 1.06a
46.36 Æ 0.84a
48.57 Æ 1.16a
45.84 Æ 0.52a
Values in the same row with different letters are significantly different at P = 0.05.
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Aquaculture Nutrition ª 2015 John Wiley & Sons Ltd

6. flounder (P. olivaceus) (Chen et al. 2005), California
yellowtail (Seriola lalandi) and white sea bass Atractoscion
nobilis (Rotman et al. 2012) were fed taurine-enriched
rotifers, larval growth, survival and body taurine were also
significantly improved. Supplementing microencapsulated
diets with taurine may also improve marine larval perfor-
mance and survival (Takeuchi et al. 2001; Salze et al.
2012).
On the contrary, studies on the freshwater species rain-
bow trout (Yokoyama & Nakazoe 1992; Boonyoung et al.
2013), channel catfish (Robinson et al. 1978) and Atlantic
salmon (Salmo salar) (Espe et al. 2012) indicated that they
have the ability to synthesize taurine from CSD pathway.
Exogenous dietary taurine did not support the performance
and survival of these fishes. However, a number of other
studies indicated that some freshwater fishes may lack the
ability of taurine synthesis through CSD pathway, and, in
turn, they may require exogenous taurine for optimum per-
formance and physiological functions. For example, taurine
supplementation (0.5%) was essential for optimal perfor-
mance of juvenile rainbow trout fed soy protein concen-
trate-based diets (Gaylord et al. 2006, 2007). Taurine
supplementation also improved growth rates, feed digest-
ibility and feed efficiency of carps (Liu et al. 2006; Luo
et al. 2006).
However, these studies were carried out on fingerling,
juvenile and grow-out stages, while the available informa-
tion on the effects of dietary taurine on larval performance
of freshwater fishes, especially Nile tilapia larvae, is very
limited. In the present study, a taurine-free diet resulted in
poor growth performance, whereas 10 g kgÀ1
dietary tau-
rine resulted in the best growth rates and feed efficiency.
However, the quadratic regression analyses indicated that
the maximum larval performance occurred at about
9.7 kgÀ1
of dietary taurine. This value is slightly higher
than that reported by Goncßalves et al. (2011). But taurine
range used by Goncßalves et al. (2011) was relatively narrow
(2–8 g kgÀ1
), and the fish may have required higher taurine
levels if wider dietary taurine range had been used. This
result may indicate that Nile tilapia larvae are unable (or
have limited ability) to synthesize taurine from methionine
through CSD pathway, despite that methionine and cyste-
ine in the test diets used in the present study were within
the range reported for optimum performance of Nile tilapia
(El-Saidy & Gaber 1998; Nguyen & Davis 2009; Furuya &
Furuya 2010). The low body taurine concentration in
the taurine-free group compared to those fed taurine-
supplemented diets may also suggest that Nile tilapia larvae
did not receive sufficient taurine from the control diet, and
supplemental taurine was necessary. Similar results have
also been reported in white shrimp (Yue et al. 2013).
In the present study, dietary taurine at 9.7 g kgÀ1
level
was sufficient for optimum performance and biological func-
tions, while further increase in taurine concentration lowered
larval performance. This suggests that when taurine was pro-
vided at higher concentrations, excessive taurine may have
been excreted to keep body taurine at optimum concentra-
tion. This process is energy-demanding, leading to increasing
energy consumption and therefore reducing or levelling off
growth performance (Yue et al. 2013). Similar findings were
reported in rainbow trout (Yokoyama & Nakazoe 1992) and
gilthead sea bream (Pinto et al. 2013). Excessive dietary tau-
rine may also lead to cessation of growth rates through
reducing feed intake as has been reported in Japanese floun-
der (Park et al. 2002) and rainbow trout (Gaylord et al.
2006). Mayasari (2005) found also that excessive exogenous
taurine reduced moulting and survival of white shrimp
(Litopenaeus vannamei) larvae. The author referred that
result to the possible poisonous effect of taurine when
provided at excessive concentrations. This may explain the
increase of fish mortality in the present study with increasing
dietary taurine concentration beyond 10 kgÀ1
.
Body protein in the present study was highest, while
body water and ash were lowest (P < 0.05) at 10 kgÀ1
die-
tary taurine. Further increase in dietary taurine led to a
decrease in body protein and an increase in both moisture
and ash contents. Similar results were reported on juvenile
turbot (Scophthalmus maximus) (Qi et al. 2012), presum-
ably due to the stimulation effect of taurine on growth by
stimulating feeding (Carr 1982) and increasing protein syn-
thesis and deposit when taurine was supplemented at opti-
mum levels (Li et al. 2009).
In the present study, body taurine was significantly
increased with increasing dietary taurine supplementation
(P < 0.05). This means that body methionine was not used
for taurine synthesis, supporting the argument that Nile
tilapia larvae lack the ability to biosynthesize taurine and
indicating that supplemental taurine is necessary for their
optimum performance. As previously mentioned, marine
fish species, such as Japanese flounder (P. olivaceus), red
sea bream (P. major) and yellowtail (S. quinqueradiata),
also have low or negligible ability of taurine synthesis due
to the absence of or low CSD activities during intermediate
metabolism from methionine to hypotaurine (Goto et al.
2001; Yokoyama et al. 2001; Park et al. 2002; Kim et al.
2003, 2005, 2008; Takagi et al. 2005, 2006a,b, 2008, 2011).
Therefore, supplemental taurine may be indispensible, par-
ticularly if they are fed plant-based feed.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aquaculture Nutrition ª 2015 John Wiley & Sons Ltd

7. In conclusion, the present study suggests that Nile tilapia
larvae lack the ability to biosynthesize taurine from methi-
onine through CSD pathway. However, more research is
needed to support this assumption. About 9.7 g kgÀ1
die-
tary taurine is required for optimum growth rates, feed effi-
ciency and survival of these fish larvae.
The authors thank GISIS Company, Ecuador, for provid-
ing the taurine that was used in the present study.
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