3.2 Chemical composition
The chemical composition depends on many factors including culture environment, the region of fishing, season and nutrition habits. In the present study, ISS fillet is characterized by a significantly higher content of protein (P = 0.008), lipid (0.006), ash (P = 0.009) and N free extract (P = 0.037) (Table 3). Consequently, we obtain a lower moisture compared to the other two groups (P = 0.003).
The difference in the mean total lipid content was particularly marked between wild and ISS sea bass (1.04 % vs 3.05 %; P = 0.006). Dietetic and practical implications may occur in consequence of this observation since wild sea bass may be considered a lean fish, while reared sea bass may not.
The higher lipid content of farmed compared to wild fish could be considered the result of the high stocking density and intensive feeding of fish in the rearing tanks [6]. Periago [14] and Fuentes [15] in a comparison of wild and farmed sea bass, showed the highest value of moisture and protein in farmed sea bass and a higher total fat in wild sea bass. In the same comparison, Baki [16] showed a higher value of moisture, crude protein and crude lipid in cultured sea bass.
Table 3
Chemical composition of filet of sea bass for each origin (%)
|
Origin1
|
|
|
|
ES
|
IRS
|
WF
|
SEM2
|
p Value
|
Moisture
|
77.33 A
|
73.07 B
|
76.75 A
|
0.684
|
0.003
|
Crude Proteins
|
19.65 B
|
21.39 A
|
19.95 B
|
0.145
|
0.008
|
Lipid
|
1.23 B
|
3.05 A
|
1.04 B
|
0.155
|
0.006
|
Ash
|
1.50 B
|
1.64 A
|
1.46 B
|
0.030
|
0.009
|
N free-extract
|
0.60 b
|
0.87 a
|
0.95 a
|
0.100
|
0.037
|
1 ES: extensive system; IRS: intensive rearing system; WF: wild fish; 2SEM: Standard error of means; a, b: p < 0.05; A, B: p < 0.01. |
3.3 Fatty acid composition of fillets
The fatty acid profiles of total lipids extracted from 3 groups of sea bass are reported in Table 4. The totality of the saturated fatty acids were higher in wild fish fillets. Moreover, the same trend agrees with results for sea bass and other fish species [14, 15, 17]. Palmitic acid (C16:0) was the primary SFA in all samples, followed by stearic acid (C18:0), with these contents being higher in wild fish as the content of C12:0 (P = 0.002), C 15:0 (P = 0.003) and C17:0 (P = 0.001). On the contrary WF recorded the lowest value of C14:0 (2.23% vs 4.04% and 5.56%; P = 0.004).
Fillets of extensive reared sea bass showed the lowest value of C16:1n9 (P = 0.002), C16:1n7 (P = 0.006), C17:1 (P = 0.002), C18:1n7 (P = 0.005), and the highest (P = 0.005) value of oleic acid (C18:1 n9), who was identified as the major monounsaturated fatty acid in cultured and wild sea bass.
With regard to PUFA, sea bass can be considered as a good source of the n-3 series fatty acids, particularly of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), showing the highest (P = 0.024 and P = 0.036) levels in wild specimens, which agrees with those of Alasalvar [18, 19]. DHA, playing a fundamental role in brain and retina development during the early stages of human life, was present in wild and farmed sea bass at comparably high levels [6].
Arachidonic acid (C20:4 n6) was found at significantly higher levels in wild fish (P = 0.006), whereas its precursor, linolenic acid (C18:2 n6), accumulated in extensive farmed fish (P = 0.007). A scarce metabolic action of the latter, due to a feedback inhibition exerted on Δ6-desaturase by the n-3 polyunsaturated fatty acids, abundantly supplied with the diet, maybe the reason for the low per cent content of arachidonic acid in farmed fish [6].
The fatty acid profiles of wild sea bass, selecting different organisms from the aquatic environment as their natural diet sources, showed species-specific patterns that were, at a certain extent, less evident in intensively reared fish fed commercial diets with similar chemical composition. Some of the differences found between the fatty acid profiles of wild and farmed fish of either species may be attributed to the different dietary regimen followed by fish in the salt lake and in intensive farming. In fact, while fish from salt lake drew nutrients from the natural resources of their habitat, whose availability presumably varied, farmed fish received always the same diet containing fish and being therefore rich in n-3 long-chain polyunsaturated fatty acids.
Table 4
Mean (± SE) fatty acid composition (% of total fatty acid methyl esters) of filet of sea bass for each origin (%)
|
Origin1
|
|
|
|
ES
|
IRS
|
WF
|
SEM2
|
p Value
|
C12:0 (lauric)
|
0.07 ab
|
0.06 b
|
0.08 a
|
0.01
|
0.034
|
C14:0 (myristic)
|
4.04 B
|
5.56 A
|
2.23 C
|
0.15
|
0.004
|
C15:0 (pentadecanoic)
|
0.50 B
|
0.56 b
|
0.67 Aa
|
0.03
|
0.003
|
C16:0 (palmitic)
|
21.96
|
21.98
|
22.99
|
0.50
|
0.058
|
C17:0 (heptadecanoic)
|
0.47 Bc
|
0.55 b
|
0.65 Aa
|
0.02
|
0.001
|
C18:0 (stearic)
|
4.93 B
|
3.88 C
|
6.65 A
|
0.13
|
0.002
|
∑ SFA3
|
31.98
|
32.60
|
33.27
|
0.66
|
0.087
|
C16:1 n9
|
0.69 C
|
0.86 B
|
0.97 A
|
0.03
|
0.002
|
C16:1 n7 (palmitoleic)
|
5.63 B
|
7.20 A
|
7.37 A
|
0.19
|
0.006
|
C17:1
|
0.33 Bc
|
0.46 b
|
0.63 Aa
|
0.04
|
0.002
|
C18:1 n9 (oleic)
|
21.59 a
|
20.24 b
|
20.54 ab
|
0.40
|
0.039
|
C18:1 n7
|
3.12 B
|
3.22 B
|
4.88 A
|
0.07
|
0.005
|
C20:1 n9 (eicosanoic)
|
3.47 B
|
4.44 A
|
1.41 C
|
0.08
|
0.005
|
∑ MUFA4
|
34.84
|
36.41
|
35.80
|
0.59
|
0.077
|
C18:2 n6 (linoleic)
|
7.65 A
|
5.06 B
|
2.24 C
|
0.20
|
0.007
|
C18:3n6 (γ- linolenic)
|
0.53 B
|
0.57 B
|
0.75 A
|
0.02
|
0.001
|
C18:3n3 (α-linolenic)
|
1.01
|
0.90
|
0.78
|
0.10
|
0.082
|
C18:4n3
|
0.94 B
|
1.68 A
|
0.85 B
|
0.09
|
0.003
|
C20:4 n6 (ARA)
|
2.60 C
|
3.70 B
|
4.28 A
|
0.14
|
0.006
|
C20:4 n3
|
1.00 A
|
0.55 B
|
0.52 B
|
0.05
|
0.004
|
C20:5 n3 (EPA)
|
5.61 c
|
6.74 a
|
6.09 b
|
0.33
|
0.024
|
C22:5 n6 (DPA)
|
0.43B
|
0.23 C
|
1.05 A
|
0.05
|
0.003
|
C22:5 n3
|
1.28 B
|
1.14 B
|
2.31 A
|
0.09
|
0.004
|
C22:6 n3 (DHA)
|
12.13 a
|
10.42 b
|
12.05 a
|
0.68
|
0.036
|
Total n-6 5
|
11.21 A
|
9.54 B
|
8.32 C
|
1.06
|
0.008
|
Total n-3 6
|
21.97
|
21.45
|
22.61
|
0.19
|
0.084
|
∑ PUFA 7
|
33.18
|
30.98
|
30.93
|
1.11
|
0.102
|
∑ UFA 8
|
68.02
|
67.39
|
66.73
|
0.85
|
0.097
|
n-3/n-6
|
1.96 B
|
2.25 B
|
2.74 A
|
0.11
|
0.007
|
A.I. 9
|
0.56 b
|
0.66 a
|
0.55 b
|
0.05
|
0.045
|
T.I. 10
|
0.34
|
0.35
|
0.35
|
0.01
|
0.061
|
1 ES: extensive system; IRS: intensive rearing system; WF: wild fish; 2 SEM: Standard error of means; 3 ∑ SFA—saturated fatty acids (sum of C12:0 + C14:0 + C15:0 + C16:0 + C17:0 + C18:0); 4 ∑ MUFA—monounsaturated fatty acids (sum of C16:1 n9 + C16:1 n7 + C17:1 + C18:1 n9 + C18:1 n7 + C20:1 n9); 5 Total n-6 (sum of C18:2 n6 + C18:3 n6 + C20:4 n6 + C22:5 n6); 6 Total n-3 (sum of C18:3 n3 + C18:4 n3 + C20:4 n3 + C20:5 n3 + C22:5 n3 + C22:6 n3); 7 ∑ PUFA—polyunsaturated fatty acids (sum of n-6 + n-3); 8 ∑ UFA – unsaturated fatty acids (sum of MUFA + PUFA); 9 A.I. – atherogenic index; 10 T.I. – thrombogenic index; a, b, c: p < 0.05; A, B, C: p < 0.01. |
There is no significant difference between wild and farmed sea bass fillets as regard the total n-3 polyunsaturated fatty acids. However, a significantly higher percentage of total n-6 polyunsaturated fatty acids was found in lipids of extensively reared fishes in comparison with the other two groups. This value influenced the ratio n-3/n-6 (P = 0.007), in fact, ES group showed a lower value in comparison with the WF ones. A higher intake of preformed long-chain PUFA in farmed fish and a different capability of sea bass to desaturate and elongate C18 PUFA could explain the low levels of PUFA found in wild sea bass. There is a need of a deeper understanding and knowledge on the fatty acid composition and the natural diet of the fish which lives in the salt lake to confirm this hypothesis.
The use of formulated feeds rich in n-3 PUFA in aquaculture – desirable from a human nutritional standpoint in consideration of the role played by n-3 PUFA in the prevention of cardiovascular and inflammatory diseases – also has a positive incidence on the growth rate and feed conversion efficiency of fish [6].
The indices of atherogenicity and of thrombogenicity are indicators assessing the level and the interrelation of some fatty acids that have effects on the occurrence of coronary heart diseases [10]. In this study, the meat of reared sea bass showed a markedly greater atherogenic (P = 0.045) compared to the other two groups, the result that confirms that the use of formulated feeds rich in n-3 PUFA in aquaculture is the best choice for human health.
Aside from the relative proportions of fatty acids in total lipids, which allowed a direct comparison of the lipid quality of fish from different sources, an estimation of the actual contents of total n-3 and n-6 PUFA in fish flesh also has an importance in view of its human consumption. In this study, because of the higher total lipid content, farmed sea bass showed higher levels of total n-3 and n-6 PUFA in their muscles compared to their wild counterparts. This observation has important nutritional implications considering that about 9.2% of the total marine fish purchased by Italian families in the year 2020 was represented by sea bass [20].