95

Comparative analysis of fatty acids profiles

in muscle and liver of Tunisian thick lipped grey mullet Chelon labrosus

reared in seawater and freshwater

Imen Rabeh a *, Khaoula Telahigue a Douha Boussoufa a,

Raouf Besbes b and M’Hamed El Cafsi a

a Université Tunis El Manar, Faculté des Sciences de Tunis, Département des Sciences Biologiques,

Unité de Physiologie et Environnement Aquatique, Campus universitaire Farhat Hached, 2092 Tunis, Tunisie

b Institut national des Sciences et Technologies de la mer (INSTM),

Centre de Monastir, Monastir, Tunisie

(Received: 19 April 2015, accepted: 31 December 2015)

Abstract: This study was conducted to determine differences between thick lipped grey mullet Chelon labrosus

reared in seawater (SW) and freshwater (FW) in terms of proximate composition and fatty acid composition. The

Juveniles of seawater originating C. labrosus were acclimated to freshwater in same conditions as their counterparts

in Seawater. Decrease in salinity led to higher moisture and lipid content and lower protein content (P < 0.05) in

muscle, but had not marked impacts on moisture and led to higher lipid content of liver . Dominant fatty acids in

both SW- and FW-reared fish were C14:0 (myristic acid), C16:0 (palmitic acid), C18:0 (stearic acid), C18:1n - 9

(oleic acid), C18:2n - 6 (linoleic acid), C20:4n-6 (Arachidonic acid), C18:3n-3 (alpha-linolenic acid), C20:5n-3

(eicosapentaenoic acid) , C22:6n - 3 (docosahexaenoic acid).The lipids of SW-reared fish contained significantly

(P< 0.05) higher level of saturated and monounsaturated fatty acids. However FW fish contained a higher level of

n-3 polyunsaturated fatty acids (PUFA), particularly docosahexaenoic acids (DHA) and eicosapentaenoic acids

(EPA). Considering the overall nutritional quality indices (n-3/ n-6, FLQ, AI and TI), the muscle of C labrosus

reared in freshwater were good sources of n-3 PUFAs particularly EPA and DHA.

Key words: Chelon labrosus, Freshwater, Seawater, Fatty acids, PUFA

Résumé: Cette étude a été menée pour comparer la composition biochimique globale et les profils en acides gras

du mulet lippu Chelon labrosus acclimatés à l'eau de mer et à l'eau douce. Les juvéniles de C. labrosus

provenant de l'eau de mer ont été acclimatés à l'eau douce durant un mois. D’après nos résultats, le stress hypo-

osmotique a engendré au niveau du muscle : une augmentation de la teneur en eau et de la teneur en lipides totaux

et une diminution des protéines. Cependant, nous avons enregistré une augmentation significative de la teneur en

lipides totaux hépatiques. Nos résultats ont montré aussi une dominance des acides gras suivants: C14:0 (Acide

myristique), C16:0 (Acide palmitique), C18:0 (Acide stéarique), C18:1n - 9 (Acide oléique), C18:2n - 6 (acide

linoléique), C20 :4n-6 (acide arachidonique), C18:3n-3 (acide alpha-linoléique), C20:5n-3 (Acide

eicosapentaénoïque), C22:6n - 3 (acide docosahexaénoïque). Les poissons d’eau de mer sont caractérisés par une

dominance des acides gras saturés et monoinsaturés alors que les poissons acclimatés à l’eau douce sont

caractérisés par l’accumulation des acides gras polyinsaturés (PUFA), en particulier l’acide docosahexaénoïque

(DHA) et l'acide eicosapentaénoïque (EPA). Considérons les valeurs des indices de la qualité nutritionnelle (n - 3 /

n - 6, FLQ, AI et TI), le muscle de Chelon labrosus acclimaté à l’eau douce peut constituer une bonne source en

AGPI particulièrement n-3.

Mots clés: Chelon labrosus, eau douce, eau de mer, acide gras, AGPI

* Corresponding author, e-mail address : rabehimen@yahoo.fr Tél : + 21626099892

Journal of the Tunisian Chemical Society, 2015, 17, 95-104

96 Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104

INTRODUCTION

Fish and fishery products are rich in high-

quality proteins, and provide high portions of

valuable polyunsaturated fatty acids

(PUFAs), liposoluble vitamins, and essential

minerals [1, 2]. The potential health benefits

of fish consumption are mainly attributed to

long chain n-3 polyunsaturated fatty acid,

especially eicosapentaenoic (EPA, C20:5 n-3),

docosahexaenoic (DHA, C22:6 n-3), and

arachidonic (C20:4 n-6) [3, 4]. These acids

cannot be synthesized by the the human body

but their inclusion in human diets is essential

[5]. PUFA are essential for the development

and function of certain organs .They can be

beneficial for the prevention of human

coronary artery disease [6], and have been

recognised to prevent inflammatory

conditions, arrhythmias, hypertension and

triacylglycerolemia, atherosclerosis, and

autoimmune disorders [7]. Due to different

effects of fatty acids on health, it is necessary

to define the nutritional quality index (NQI)

with regard to the fatty acid profile and their

biological functions. The nutritional quality

index is estimated by several indices of fatty

acid composition; the indices of atherogenicity

(IA) and thrombogenicity (IT), according to

[8], EPA + DHA, according to [9], n-3/n-6

PUFA ratios according to [10] .

The biochemical composition of fish is

influenced by a number of factors such as

biological variations (species, sex, size and

age), diet and seasonal changes [11]. It is also

recognized that environmental factors such as

temperature [12], salinity, light exert an effect

on the lipid contents and fatty acid

composition of aquatic organisms.

In this respect, many authors showed that

water salinity has the potential to influence

fatty acid composition of fish tissues [13, 14,

15 et 16] particularly the PUFA levels of fish

and then n-3/n-6 FA ratio, which is an

important parameter to appraise fish nutrition

and its safety [17] .

In Tunisia, the aquaculture production is at

present 9000 tons per year among which 7272

tons from marine farming and 1000 tons of

continental fish farming. The main produced

species are, the sea bass, the sea bream and the

mullet. The fish species selected for this study

is the thick lip grey mullet Chelon labrosus

(Mugilidae). It is a marine euryhaline teleost,

very common in estuaries and coastal waters

and is useful specie for semi intensive and

extensive aquaculture in Tunisia [18].

Furthermore, mullet farming contributes to

satisfy the increased local market’s demands

which are commonly used by local people. As

a contribution to sustain national effort on

freshwater aquaculture, the objective of this

study was to compare the fatty acid profiles of

grey mullet reared in seawater and freshwater

fed with the same diet and if freshwater fish

are as good a source of these fatty acids as are

marine fish.

MATERIAL AND METHODS

1. Fish, rearing conditions and diet

Immature thick lipped grey mullet (Chelon

labrosus) (30-40g body mass) were provided

by an experimental fish culturing centre

(INSTM- Centre de Monastir- Tunisia) and

transferred to the laboratory at Tunis faculty of

sciences. Animals were acclimated to

Seawater (38 ppt.salinity) in a closed system at

least 30 days before the experiment. During

the experiments fish were maintained under

natural photoperiod (12h/12h) and temperature

(18-20°C). Fish were fed once daily with local

semi-wet feed at ration of 1% of the estimated

body weight. Feed composition was: 35 %

humidity, 37% crude protein, 13% crude fat

and 2% ash (434 kcal / 100 g of feed) [19].

Fishes were fasted for 24 h before sampling in

all experiments conducted.

2. Experimental design

Before transfer, 8 SW-adapted fish were

sampled on day 0 to form the pre-transfer

control group (time 0). SW-adapted fish were

transferred directly to low salinity water (FW,

0,5 ppt), and acclimated to the new salinity for

30 days. At the end of the experiment (day

30), fishes were netted and anaesthetized with

2-phenoxyethanol (1 ml l−1), weighed and

Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104 97

sampled. Liver and a portion of white muscle

were removed quickly from each fish, frozen

in liquid nitrogen, and stored at - 80° C until

assay.

3. Proximate composition analysis

Moisture content was determined

gravimetrically. Tissues were initially

weighted and then dried at 103°C to constant

weight. Water Content was expressed as a

percentage of initial tissue mass. Tissue

protein was determined using the

bicinchoninic acid method with BCA protein

kit (Pierce, Rockford, USA) for microplates,

with bovine serum albumin as standard. Those

assays were adapted to 96-well microplates

and run on a PowerWaveTM 340 microplate

spectrophotometer (BioTek Instruments,

Winooski, VT, USA) using KCjunior. Data

Analysis Software for Microsoft® Windows

XP. Total lipids were extracted following the

method of [20] using chloroform/methanol

(2:1 v/v) as the solvent containing 0.01%

butylated hydroxy toluene (BHT) as

antioxidant. The organic solvent was

evaporated under a stream of nitrogen and the

lipid content was determined gravimetrically.

Then, the extracted lipids were resuspended in

chloroform/methanol (2:1 v/v) and stored at -

30°C prior to gas chromatographic analysis.

4. Fatty acid analysis

After evaporation to dryness, lipid extracts

were trans-esterified according to [21] method.

Methyl nonadecanoate C19:0 (Sigma) was

added as internal standard. Separation of

FAMEs was carried out on a HP 6890 gas

chromatograph with a split/splitless injector

equipped with a flame ionisation detector at

275°C, and a 30 m HP Innowax capillary

column with an internal diameter of 250 µm

and a 0.25 µm film thickness. Injector

temperature was held at 250°C. The oven was

programmed to rise from 50 to 180 °C at a rate

of 4 °C/min, from 180 to 220°C at 1.33°C/min

and to stabilize at 220°C for 7 min. Carrier gas

was nitrogen. Identification of FAMEs was

based on the comparison of their retention

times with those of a mixture of methyl esters

(SUPELCO PUFA-3) and to well-

characterized fish oil (Mehaden oil by

Supelco). Fatty acid peaks were integrated and

analysed using HP chemstation software.

5. Indices of lipid quality

From the data on the fatty-acid composition,

the following were calculated:

1) Index of atherogenicity (IA): indicating the

relationship between the sum of the main

saturated fatty acids and that of the main

classes of unsaturated, the former being

considered pro-atherogenic (favouring the

adhesion of lipids to cells of the

immunological and circula-tory system), and

the latter anti-atherogenic (inhibiting the

aggregation of plaque and diminishing the

levels of esterified fatty acid, cholesterol, and

phospholipids, thereby preventing the

appearance of micro- and macro- coronary

diseases) [22]. The following equation was

applied:

IA= [(12:0+ (4×14:0) +16:0)] /

[ΣMUFAs+PUFAn6+PUFAn3]

2) Index of thrombogenicity (IT): showing the

tendency to form clots in the blood vessels.

This is defined as the relationship between the

pro-thrombogenetic (saturated) and the anti-

thrombogenetic fatty acids [22].

The following equation was applied:

IT= (C14:0+C16:0+C18:0) / (0.50*MUFA)

+ (0.5*PUFA n-6) + (3* PUFA n-3)

+ (PUFA n-3 / PUFA n-6)

A Flesh lipid quality (FLQ) index indicating

the percentage relationship in which the main

HUFA n-3 (EPA and DHA) appear in muscle

with respect to the totality of the lipids was

calculated as the following formula suggested

by [23].

FLQ% = [(EPA + DHA) / lipid] x 100

98 Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104

Statistical analysis

Data were analysed using the software

Statistica Version 8.0 to assess significant

differences between means according to the

one way analysis of variance method

(ANOVA). For this, the Duncan test was

applied and differences were considered

significant when p < 0.05.

RESULTS AND DISCUSSION

1. Biochemical composition of diet

The proximate biochemical composition of

diet used for Chelon labrosus in the

experiment are presented in Table I. The fish

feed contained 37 % protein in order to cover

fish protein needs and, more particularly, fish

amino acid needs [24]. Lipids were 13 %.

Twenty six fatty acids were detected in the diet

(Table I), which included saturated fatty acids

(SFAs), monounsaturated fatty acids

(MUFAs), n-6 PUFAs and n-3 PUFAs. The

characterized fatty acid in SFAs, MUFAs, n-6

PUFAs and n-3 PUFAs was: C16:0, C18:1,

C18:2n-6 and C20:5n-3, respectively.

2. Proximate composition

Results of proximate analysis of C. labrosus

reared in seawater and freshwater are shown in

Table II. Salinity affected the biochemical

composition of muscle tissue significantly.

Lower muscle moisture was detected in SW

fish, while muscle crude protein and crude

lipid contents in the SW group demonstrated

markedly higher values than those in the FW

group. Similar result was also reported in

rainbow trout [25], red drum [26]; milk fish

[27]; Japanese Sea bass [28] and yellow’eels

[15]. Increasing muscle protein and lipid

contents in the SW might result from lower

energy requirements for osmoregulation in SW

than in FW because fingerlings in this

experiment originated from marine waters.

Salinity showed no marked impacts on the

water content (Moisture) of liver in the two

groups. Protein content was significantly

decreased (P<0.05), while total lipid content

was significantly increased (P<0.05) by

decrease in salinity. The present study showed

Proximate composition (%)

Crude protein 37

Crude lipid 13

Ash 2

Fatty acid (%)

SFA 31.56

MUFA 31.71

PUFA 36.71

n-3 11.58

n-6 22.62

n-3/ n-6 0.511

C14 :0 5.99

C15 :0 0.30

C16 :0 21.84

C17 :0 0.39

C18 :0 3.04

C20 :0 0.02

C15 :1 0.50

C16 :1 5.67

C18 :1 24.12

C20 :1 1.43

C18 :2n-6 22.03

C20 :2n-6 0.14

C20 : 3n-6 0.02

C20 :4n-6 0.27

C22 :5n-6 0.17

C18 :3n-3 3.81

C18 :4n-3 1.41

C20 :3n-3 0.04

C20 :4n-3 0.21

C20 :5n-3 3.52

C22 :5n-3 0.37

C22 :6n-3 2.23

C16 :2 0.90

C16 :3 0.93

C16 :4 0.50

C21 :5 0.19

Table I. Proximate composition (%) and fatty acids

profiles (% of total lipids) of the experimental diet of

Chelon labrosus.

Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104 99

that salinity had marked impact (P<0.05) on

proximate composition of liver (Table II).

These results were opposite to the findings of

[28, 2] in Japanese sea bass and Capoeta

damascina respectively reared in seawater and

freshwater.

3. Fatty acid profile

The fatty acid profiles of muscle and liver of

Chelon labrosus reared in SW and FW are

presented in Table III. Fatty acid types in

muscle, liver for the two groups were similar.

This fatty acid pattern is similar to some other

fish species (Oreochromis niloticus: [29],

Maccullochella peelii : [30]; Perca fluviatilis :

[31]; Lateolabrax japonicus : [29]; [32]) and

also coincided with the fatty acid types in the

diet. Out of 29 fatty acids are detected, and

identified in a range from C14: 0 to C22:6n-3.

There were considerable differences among

the fish studied in terms of the FA composition

although they were fed the same diet. This

finding can be explained on the basis of

previous studies reports that the biochemical

composition of fish particularly fatty acids was

influenced by rearing conditions, such as

salinity [14, 16, 27, and 28]. The fatty acids

analyzed were grouped as saturated (SFA),

Table II. Proximate composition of muscle and liver of

Tunisian Chelon labrosus reared in seawater and

freshwater. Different letters indicate significant

differences between groups (p < 0.05, one-way

ANOVADuncan’s test).

Seawater Freshwater

Muscle

Moisture (%) 56± 0,2a 63±0,1b

Protein (mg /g PF) 18,9± 2a 9±1,9b

Total lipids (mg/.g PF ) 49,79±0,5a 17,95±0,09b

Liver

Moisture (%) 48± 0,9a 50±0 ,1a

Protein (mg /g PF) 17,2±0 ,07a 9,6±0,8b

Total lipids (mg/.g PF) 71,74±0, 5a 81,68± 0,1b

monounsaturated (MUFA) while di-, tri-, tetra-,

penta- and hexa-noic fatty acids were grouped

as polyunsaturated fatty acids (PUFA).

Dominant fatty acids in both SW- and FW-

reared fish were C14:0 (myristic acid), C16:0

(palmitic acid), C18:0 (stearic acid), C18:1n -

9 (oleic acid), C18:2n - 6 (linoleic acid),

C18:3n-6 (gamma-linolenic acid), C18:3n-3

( a lp ha - l i no le n ic a c id ) , C 20 :5 n - 3

(eicosapentaenoic acid), C22:6n - 3 (docosa-

hexaenoic acid) (Table III).

For the muscle, and the liver, the percentage of

total SFA was lower in FW fish compared

with SW fish. The Palmitic acid (C16:0) was

the major saturated fatty acids (SFA), in both

tissues of the two groups .The percentage of

this acid was 26.75% and 14.66 % in SW and

FW muscle tissue, respectively (p < 0.05), and

27.43% (in SW) and 13.05% (in FW) in the

liver (p < 0.05). The same observations were

cited by [18, 33, 34, and 35]. Myristic acid

(C14:0) and Stearic acid (C18:0) were the fatty

acids presents at the second highest levels. In

SW, Myristic acid (C14:0) (6.46 % in muscle,

5.19 % in liver) was higher than Stearic acid

(C18:0) (2.82 % in muscle, 4.36% in liver) for

both tissues, as can be seen from Table III.

Similar results have been reported by [31].The

Oleic acid (C18:1) was identified as the major

monounsaturated fatty acid (MUFA) in liver

and muscle of both groups, presumably due to

its dominance in the commercial feed used in

this experiment . Moreover, this fatty acid was

higher in SW tissues (23.55% (muscle) and

26.23% (liver)) than in FW (12.74% and

16.71%, respectively; p < 0.05)) (Table

III).Oleic acid (C18:1) is a characteristic

MUFA in fish tissues [18]. In rainbow trout

(Oncorhynchus mykiss) C18:1 is the

predominant MUFA in both liver and muscle

[19, 36, 17]. The palmitoleic acid (C16:1) was

another notable fatty acid in the MUFA

fraction in both tissues .This acid was

significantly decreased (P < 0.05) by decrease

in salinity (Table III). The mentioned results

are contractory with the reports for Japanese

sea bass reared in seawater and freshwater

[29] and Capoeta damascina reared in

100 Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104

Fatty acids Muscle Liver

FW SW FW SW

SFA 36.94± 0.23a 30.68± 0.37b 38.83± 0.10a 20.78± 0.37b

MUFA 34.20± 0.09a 18.93± 0.36b 35.52± 0.24a 25.31± 0.14b

PUFA 28.87± 0.29a 50.13± 0.38b 25.61± 0.28a 53.51± 0.52b

n-3 14.74± 0.37a 32.34± 0.27b 11.12± 0.50a 27.70± 1.01b

n-6 11.03± 0.29a 13.92± 0.34b 12.65± 0.22a 21.85± 0.52b

C14 :0 6.46± 0.13a 2.13± 0.09b 5.19± 0.03a 2.15± 0.04b

C15 :0 0.46± 0.03a 0.29± 0.08b 0.66± 0.02a 0.45± 0.03b

C16 :0 26.75± 0.22a 14.66± 0.46b 27.43± 0.37a 13.05± 0.04b

C17 :0 0.44± 0.01a 0.52± 0.06a 0.66± 0.02a 0.65± 0.02a

C18 :0 2.82± 0.07a 12.11± 0.05 b 4.36± 0.11 3.55± 0.34

C20 :0 0.02± 0.00a 0.22± 0.01b 0.001± 0.00 a 0.19± 0.06b

C22 :0 0.002± 0.00a 0.75± 0.03b 0.53± 0.09a 0.73± 0.03b

C15 :1 0.91± 0.10a 0.34± 0.03b 0.80± 0.02a 0.44± 0.04b

C16 :1 8.30± 0.06a 2.85± 0.14b 8.41± 0.01a 4.66± 0.07b

C18 :1 23.55± 0.03a 12.75± 0.59b 26.23± 0.26a 16.71± 0.53b

C20 :1 1.44± 0.03a 1.62± 0.34a 0.01± 0.00a 1.47± 0.20b

C22 :1 0.00± 0.00a 1.37± 0.07b 0.06± 0.01a 2.02± 0.19b

C18 :2n-6 9.25± 0.26a 7.56± 0.11b 10.90± 0.12a 12.34± 0.14b

C18 :3n-6 0.21± 0.02a 0.23± 0.02a 0.17± 0.00a 0.37± 0.03b

C20 :2n-6 0.20± 0.02a 0.65± 0.01b 0.33± 0.01a 1.47± 0.10b

C20 :3n-6 0.07± 0.01a 0.90± 0.08b 0.05± 0.02a 0.85± 0.03b

C20 :4n-6 0.97± 0.03a 2.16± 0.10b 0.70± 0.02a 1.67± 0.19b

C22 :5n-6 0.34± 0.03a 2.41± 0.51b 0.50± 0.05a 5.14± 0.19b

C18 :3n-3 1.63± 0.46a 3.56± 0.39b 1.99± 0.03a 2.29± 0.41b

C18 :4n-3 1.08± 0.08a 1.30± 0.08b 0.73± 0.00a 2.62± 0.22b

C20 :3n-3 0.08± 0.01a 0.54± 0.05b 0.10± 0.01a 1.22± 0.14b

C20 :4n-3 0.35± 0.04a 0.98± 0.07b 0.32± 0.01a 1.56± 0.33b

C20 :5n-3 4.94± 0.18a 8.23± 0.20b 2.96± 0.07a 5.46± 0.25b

C22 :5n-3 1.15± 0.07a 3.20± 0.03b 1.10± 0.38a 4.15± 0.86b

C22 :6n-3 5.51± 0.01a 14.54± 0.18b 3.93± 0.24a 10.40± 0.10b

C16 :2 1.12± 0.05a 0.65± 0.04b 0.99± 0.00a 0.44± 0.03b

C16 :3 0.93± 0.14a 0.49± 0.06b 0.27± 0.01a 0.64± 0.05b

C16 :4 0.79± 0.04a 0.27± 0.04b 0.25± 0.00a 0.33± 0.04a

C21 :5 0.25± 0.04a 2.46± 0.37b 0.32± 0.01a 2.57± 0.14b

Table III. Fatty acid profiles (% of total fatty acids) of muscle and liver of Tunisian Chelon labrosus reared in

seawater and freshwater (mean ± SE, n = 6; superscript letters indicate inter group statistical differences, p < 0.05).

freshwater and brackish water [2,37] reported

that the main MUFA were palmitoleic (C16:1)

and oleic (C18:1) and were common in fish

among mono-unsaturated fatty acids which,

are in good agreement with the present

findings.

In muscle and also liver, salinity significantly

increased (P < 0.05) the content of total

polyunsaturated fatty acids (PUFAs) in a dose-

dependent manner (Table III). The role of

PUFAs in membrane plasticity may be one of

the factors accounting for the differences in

Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104 101

content of this family of fatty acids between

saline water and freshwater-reared fishes [38].

Among n-6 series of fatty acids, C18:2n-6 was

the one of the predominant polyunsaturated

fatty acid (PUFA) in both tissues of SW- and

FW-reared fish. C18:2n-6 which is essential in

human nutrition as these fatty acids are not

synthesized in the body but these are required

for the tissue development]. This fatty acid is

contained in plant oil included in the feed of

cultured fish [39] thus the higher amount of

linoleic acid in farmed fish is related to the

feed ingredients and chain elongation and

desaturation capacity [2].The arachidonic

ARA (C20:4 n-6) was at the highest amounts

in FW with values of 1.67-2.41 % in muscles

and 2.16-5.14% in livers (p <0.05). Similar

results for liver and muscle of S. trutta

macrostigma have been reported [37].

Arachidonic acid (C20:4), is a precursor for

prostaglandin and thromboxane biosynthesis

which are produced as a response to

environmental stress [40]. In this study,

freshwater conditions are an environmental

stress to seawater originating C. labrosus

juveniles.

Total n-3 PUFA level showed clear differences

in SW (14.74%) and FW (32.34%) muscles, as

did in SW (11.12%) and FW (27.70 %) livers

(p< 0.05).Eicosapentaenoic acid (EPA) and

docosahexaenoic acid (DHA) were the major

fatty acids identified as n- 3 PUFAs in muscle

and liver, however the content of both fatty

acids was significantly increased (P < 0.05) by

decreased salinity. DHA (C22:6n-3) was found

to be at the highest level in the n-3 PUFA

fraction in the SW and FW tissues studied. FW

muscle had substantial levels of C22:6 n-3

with a value of 14.54%, higher than in livers

(10.40%; p < 0.05). EPA (C20:5 n-3) was the

fatty acid at the second high amount in n-3

PUFA of fish tissues. High levels of EPA and

DHA were reported by other studies and

marine fish species [25, 32, 37, 38,].

The results shown in Table III indicated that

the tissues fish analysed from FW were

characterized by high levels of n-3 fatty acids

than n-6 fatty acids.

However, we recorded opposite results with

those obtained in other studies where wild

freshwater fish were mainly characterised by

the elevated levels of n-6 PUFA especially

linoleic (18:2) and arachidonic (20:4) acids

[36, 37].

The trend of fatty acids of fish from seawater

is different when compared to the freshwater

fish, where the percentages of the saturated

and mono-unsaturated fatty acids were higher

than poly-unsaturated fatty acids. The PUFA

n-3, n-6, were higher compared to MUFA and

SFA in liver and muscle freshwater fish which

was in agreement with a similar study carried

out by [44] .It seemed probably that fish in FW

predominantly used SFAs and PUFAs for

energy production than those in SW for

osmoregulation as FW species have to excrete

higher amount of water from body to the hypo-

osmotic environment [2] or for the synthesis of

PUFA. Similar results have been reported

previously for the European sea bass [41] and

in rainbow trout, Oncorhyncus mykiss [34].

The data in the literature indicate that both

marine and freshwater fish are good sources of

polyunsaturated fatty acids [42]. EPA and

DHA are only found in fish and sea food and

possess extremely beneficial properties for the

prevention of human coronary artery diseases

[43]. A number of countries including Canada

and the United Kingdom, and organizations

such as the World Health Organization (WHO)

and North Atlantic Treaty Organization have

advocated dietary recommendations for n-3

PUFAs. General recommendation for daily

intakes of DHA/EPA is 0.5 g for infants and

1g/day for adults and patients with heart

disease and 0.3 to 0.5 mg/day EPA + DHA.

Based on the results in Table IV, these

recommendations can easily be met by

consuming 1 g fresh of muscle of C.labrosus

reared in seawater or in freshwater.

The n-3/n-6 fatty acids ratio has been

suggested to be a useful indicator for

comparing relative nutritional values of fish

oils [44].In the present study , the n-3/n-6

ratios in SW and FW livers were found to be

0.88 and 1.27 (p < 0.05), while in muscles the

102 Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104

Table IV: Amounts of total PUFA, n-3, n-6, DHA,

EPA (mg/.g PF) and ratio of EPA+DHA of muscle of

Chelon labrosus reared in seawater and freshwater.

ratios were 0.7 and 2.5 as (p < 0.05)

respectively.When compared with SW fish,

the FW fish used in our study have a higher n-

3/n-6 ratio. The n - 3/n - 6 ratio shown in the

study is consistent with that determined

between wild and reared gilthead sea bream

(Sparus aurata) and pike (Esox lucius) [ 45,

46], but differs from that determined in

Atlantic salmon (Salmo salar), rainbow trout

and European eel (Anguilla anguilla) as well

as sea bass (Dicentrarchus labrax.), indicating

the lower n - 3/n - 6 value in reared fish [47].

EPA and DHA are long chain n-3 fatty acids

that are precursors of hormones known as

eicosanoids which play important roles in

biological processes within the body.

Consequently, ‘EPA + DHA’ is one of the

most important nutritional quality indexes. In

our study, freshwater fish have a higher EPA +

DHA (P < 0.05). The higher value of this

index, the greater the quality of the dietary

lipid source.

Muscle Seawater Freshwater

PUFA 6,65±1,2 a 8,09 ±0,5b

n-3 3,16± 0,15a 5,30 ±0,64 b

n-6 2,74±0,86a 2,19±0,65b

DHA 1,13±0,03a 2,35±0,1b

EPA 1,02± 0,01a 1,15±0,12a

EPA+DHA 2,15±0,01a 3,85±0,53b

Table V: Lipid quality indices of muscle and liver of Tunisian Chelon labrosus reared in seawater and freshwater.

Different letters indicate significant differences between groups (p < 0.05, one-way ANOVADuncan’s test).

Lipid index Liver Muscle

SW FW SW FW

n-3/ n-6 0,7 ± 0,06a 2,51± 0,20b 0,88± 0,05a 1,27±0,08b

AI 0,88 ± 0,01a 0,35± 0,002b 0,81 ±0,04a 0,29±0,01b

TI 0,53 ± 0,01a 0,21± 0,073b 0,63 ±0,02a 0,17±0,01b

FLQ 10,45±0,18a 22,77± 0,023b 6,89 ±0,17a 15,85±0,19b

The average of atherogenic and thrombogenic

index values were almost lower in fish reared

in freshwater (Table IV). The IA correlates

proatherogenic (sum of 12:0, 14:0 and 16:0)

with anti-atherogenic fatty acids (sum of

monounsaturated and n3 and n6

polyunsaturated fatty acids). The IT considers

the fatty acids 12:0, 14:0 and 16:0 to be

thrombogenic, and the monunsaturated, n-3

and n-6 polyunsaturated fatty acids to be anti-

thrombogenic. Moreover, it attributes a higher

ant i- t hr o mbo gen ic e f fec t t o n - 3

polyunsaturated fatty acids than to

monounsaturated and n6 polyunsaturated fatty

acids [48].

However, our study has revealed that chelon

labrosus is a farmed fish species having a high

nutritional value for human consumption.

CONCLUSIONS

The mentioned studies showed that water

salinity can affect the proximate composition

and fatty acid profile, particularly PUFA levels

of fish and then n-3 /n-6 ratio which is a

reliable indicator to assess the nutritive value

of lipids. Freshwater Chelon labrosus showed

a higher level of DHA, EPA and n-3/n-6 ratio.

Despite lower tissue DHA, EPA and n-3/n-6

ratio of seawater Chelon labrosus, both are

nutritious and safe fish products according to

the n-3/n-6 values. In summarising the results

obtained, it may be concluded that the semi

intensive rearing of Chelon labrosus in both

seawater and freshwater produces fish whose

muscle and liver lipids do not diverge from

those of wild fish in terms of contents of EPA

Imen Rabeh et al., J. Soc. Chim. Tunisie, 2015, 17, 95-104 103

and DHA acids, the most valuable to a

consumer.

Acknowledgments: This work was supported by the

research project entitled TENMIA funded by the

Tunisian Ministry of Scientific Research, Technology

and Development of Competences.

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