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 kg1 protein), isoener-

getic (19 MJ kg1) diets supplemented with four taurine

concentrations (0.0, 5.0, 10.0 and 15.0 g kg1; 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 kg1 and decreased with

further taurine supplementation. The quadratic regression

analyses indicated that the maximum larval performance

occurred at about 9.7 g kg1 of total dietary taurine. Fish

survival was significantly lower at 15 g kg1 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 kg1 and decreased

with further taurine supplementation to 15 g kg1. 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 kg1 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 kg1 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,

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2015 John Wiley & Sons Ltd

2015 doi: 10.1111/anu.12266. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Aquaculture Nutrition

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 3050% 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 (Goncalves 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 (Goncalves et al. 2011). The preliminary results ofthat study revealed that the larvae require 8 g kg1 taurine

for optimum performance. However, the taurine range used

in that study was relatively narrow (28 g kg1); 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 2015 John Wiley & Sons Ltd

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 1 C, while natural light was usedthroughout 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 (NH4N), nitrates (NO3N), nitrites

(NO2N) 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 1.2 mg L1, pH = 7.8 0.10, NH4N = 0.081 0.002 mg L1, NO3N = 0.72 1.61 mg L1and NO2N = 0.00 mg L

1.

Four SBM-based, isonitrogenous (400 g kg1 cp), isoener-

getic (19 MJ kg1) diets were prepared, containing four

concentrations of taurine (0.0, 5.0, 10.0 and 15.0 g kg1;

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 kg1) 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 kg1) 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 20 C for final body composition and amino acidanalyses. 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

20 C for chemical analysis. Proximate analysis of mois-ture, protein, lipid and ash was performed according to

Table 1 Composition and proximate analysis (g kg1 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 kg1 or IU kg1 of dry vitamins & minerals powder: Vit. A 2 200 000 IU., Vit. D3 1 100 000I.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 g1 for protein, lipid and carbohydrate, respectively.

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Aquaculture Nutrition 2015 John Wiley & Sons Ltd

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) 100 Wf Wi=Wi;

Specific growth rate % SGR 100 ln Wf lnWi=t;where Wi and Wf are initial and final weights (g), and t is

the time of experiment (days).

Feed conversion ratio (FCR) dry feed intake (g)=fish live weight gain (g):

Protein productive value (PPV) 100 protein gain (g)=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.

Duncans 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 kg1 and decreased with further taurine

supplementation. The quadratic regression analyses indi-

cated that the maximum larval performance occurred at

9.7 g kg1 of total dietary taurine. The equations represent-

ing the relationships between fish performance (y) and die-

tary taurine (x) were as follows:

PWG : y 36:261x2 707:82x 4001:9;R2 0:7887SGR : y 0:0095x2 0:1836x 6:3169;R2 0:8215FCR : y 0:0049x2 0:0947x 1:5949;R2 0:7825

Larval survival was not significantly affected by taurine

supplementation up to 10 kg1 (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 SEM) of Nile tilapia fry

Growth parameter

Experimental diets

T0 T0.5 T1 T1.5

Initial weight (g fish1) 0.024 0.024 0.024 0.024Final weight (g fish1) 1.18 0.011d 1.61 0.02b 1.94 0.08a 1.46 0.03cPercentage weight gain 4817 48d 6608 87b 7997 337a 5983 127cSpecific growth rate 6.49 0.02d 7.01 0.02b 7.32 0.07a 6.84 0.04cFeed consumed (g fish1) 1.82 0.087b 2.44 0.050a 2.68 0.017a 2.43 0.044aFeed conversion ratio 1.57 0.05b 1.54 0.05b 1.40 0.07a 1.69 0.02cProtein productive value 23.32 0.85c 27.39 1.24b 35.55 2.24a 26.22 0.22bSurvival (%) 84.50 0.29a 86.33 4.06a 85.33 2.33a 75.34 1.45b

Values in the same row with different letters are significantly different at P = 0.05.

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Aquaculture Nutrition 2015 John Wiley & Sons Ltd

supplemental taurine to 15 kg1 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 kg1 and increased afterwards.

Body protein significantly increased with increasing dietary

taurine up to 10 kg1 and levelled off with further taurine

supplementation to 15 kg1. Body lipid was also signifi-

cantly increased with increasing supplemental taurine up to

10 kg1 and decreased with further taurine supplementa-

tion to 15 kg1.

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 kg1 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 kg1) (mean SEM) on wet weight basis of Nile tilapia larvae fed the test diets

Composition (g kg1) Initial

Experimental diets

T0 T0.5 T1 T1.5

Moisture 692.00 740.22 2.82a 729.41 2.37a 683.13 3.3b 703.20 1.56cProtein 187.89 147.82 1.72a 166.00 0.25b 168.91 0.38c 168.07 1.23cLipid 40.69 44.85 0.36a 51.11 1.19b 58.24 1.96c 54.69 1.86dAsh 85.62 66.35 0.26b 60.87 1.58a 66.73 2.94b 72.21 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 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 0.04a 3.71 0.01a 3.90 0.02a 3.63 0.16aMethionine 1.47 0.012a 1.42 0.08a 1.37 0.13a 1.42 0.09aThreonine 1.87 0.08b 2.19 0.005a 2.31 0.01a 1.91 0.05bTryptophan 0.54 0.003d 0.60 0.005b 0.65 0.007a 0.58 0.001cArginine 2.46 0.05c 2.79 0.09b 3.09 0.016a 2.60 0.04bcPhenylalanine 1.79 0.11a 1.79 0.066a 1.90 0.05a 1.83 0.019aHistidine 1.22 0.017d 1.59 0.035b 1.74 0.040a 1.29 0.004cIsoleucine 2.64 0.011b 2.67 0.02b 2.85 0.051a 2.70 0.004bLeucine 3.29 0.02b 3.52 0.035a 3.72 0.013a 3.59 0.13aValine 2.43 0.08b 2.71 0.11ab 2.85 0.027a 2.65 0.05abCysteine 0.77 0.011a 0.72 0.026a 0.74 0.004a 0.78 0.032aAlanine 2.93 0.02b 2.95 0.035b 3.16 0.05a 2.91 0.048bGlutamic acid 6.57 0.34a 6.91 0.29a 6.79 0.76a 6.32 0.11aGlycine 2.60 0.02c 2.73 0.025b 2.87 0.045a 2.66 0.015bcSerine 1.74 0.07a 1.57 0.005a 1.71 0.02a 1.76 0.22aAspartic acid 5.58 0.25a 4.98 0.17a 4.93 0.03a 5.06 0.18aProline 3.10 0.20a 2.69 0.16a 2.82 0.065a 3.05 0.19aTaurine 0.13 0.003c 0.74 0.04b 1.09 0.09a 1.15 0.06aTotal 44.83 1.06a 46.36 0.84a 48.57 1.16a 45.84 0.52a

Values in the same row with different letters are significantly different at P = 0.05.

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Aquaculture Nutrition 2015 John Wiley & Sons Ltd

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 kg1 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 kg1 of dietary taurine. This value is slightly higher

than that reported by Goncalves et al. (2011). But taurinerange used by Goncalves et al. (2011) was relatively narrow(28 g kg1), 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 kg1 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 kg1.

Body protein in the present study was highest, while

body water and ash were lowest (P < 0.05) at 10 kg1 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 2015 John Wiley & Sons Ltd

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 kg1 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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