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Mean values and standard deviation for each fatty acid were calculated first. The results were subjected to a one-way ANOVA to test the effect of the replacement of vegetable oil on fatty acid profile. Data were analyzed using statistical packages SPSS v15 (SPSS Inc., Chicago, IL, USA). Differences between means were compared using Duncan's

multiple range test at significance of differences (P<0.05) among dietary treatments.Linear regression analyses were performed between dietary and fillet fatty acid concentrations.

Results

Fatty acids composition of the oils, experimental diets, fillet sample from initial and each of the replicates at the end of experiment and correlation between dietary fatty acids concentrations and fatty acids concentrations in fillet are presented in Table 1.

The fish oil diet (FOD) contained the highest level of SFAs (33.3%)

predominantly in the form of palmitic (16:0) and stearic acids (18:0) which accounted for (22.7%) and (5.8%), respectively. Monounsaturated fatty acids (MUFAs) concentrations were highest in the FOD (48.6%), but oleic acid concentration was highest in the flaxseed oil diet (FxOD) (18:1n-9, 41.7%). The FxOD was richest in PUFAs (n-6+n-3) (27.3%) with a-

linolenic acid (18:3n-3, 22.0%) and linoleic acid (18:2n-6, 0.4%) as the principal fatty acids. The highest levels of EPA and DHA were in the FOD, with 2.9% and 6.6%, respectively. Fatty acids of the n-3 and n-6 series were observed in highest concentration in the FxOD and FOD respectively, which accounted for (25.8%) and (2.9%), respectively. Levels of HUFAs n-3 were found in highest concentrations in the FOD with 9.6%.

The major fatty acid classes (SFAs, MUFAs and PUFAs) found in the highest concentration were palmitic, oleic, a-linolenic acids along with DHA, respectively. The level of SFAs was observed in higher (P<0.05) concentrations for fish fed the FOD compared to fish fed the FxOD and

FFxOD. Levels of MUFAs ranged from 47.4+0.5 (FxOD) to 53.0+0.4

(FOD) and were observed to be significantly higher in fish fed the FOD. The fillet of fish fed the FOD and FxOD were particularly rich in oleic acid (44.8+0.4%) and a-linolenic acid (19.3+0.4%), respectively. DHA and arachidonic acid levels were found in higher concentrations in the fillet than in the diets. The highest level of EPA and DHA was observed

in fish fed the FOD (P<0.05).

Table 1. Fatty acids composition (percentage of total fatty acids) of the oils, experimental diets and rainbow trout reared on the experimental diets and correlation between dietary fatty acids concentrations and fatty acids concentrations in fillet of rainbow trout fed the experimental diets for 8 weeks.

Experimental diets

Rainbow Trout reared on the experimental diets (mean+SD)

Fish

Oil

Flaxseed

Oil

correlation between dietary fatty acids concentrations and fatty acids concentrations in fillet Correlation coefficient

(r)

Slope

16:0

20.73

6.79

22.71

16.48

19.80

10.11

17.45+0.29a

12.46+0.12c

14.42+0.26b

0.974

0.719

18:0

4.16

4.48

5.85

6.04

6.20

2.90

4.46+0.10a

4.59+0.07a

4.27+0.06b

0.451

0.201

SFAs (others)

4.79

1.95

4.76

3.70

4.29

5.43

5.83

4.79

5.46

 

 

SFAs

29.68

13.22

33.32

26.22

30.29

18.44

27.74+0.53a

21.84+0.20c

24.15+0.25b

0.957

0.757

16:1n-7

5.24

0.34

4.92

2.59

3.86

1.77

4.49+0.09a

2.35+0.03c

3.28+0.09b

 

 

18:1n-9

33.57

34.19

38.79

41.75

40.50

61.25

44.85+0.45a

43.25+0.63b

44.71+0.15a

0.861

-0.513

MUFAs (others)

5.71

0.39

4.88

2.16

3.49

1.86

3.65

1.8

2.61

 

 

MUFAs

44.52

34.92

48.59

46.50

47.85

64.88

52.99+0.38a

47.40+0.52c

50.60+0.02b

0.997

2.637

18:2n-6

0.37

0.38

0.42

0.39

0.61

0.71

0.41+0.05

0.52+0.09

0.42+0.02

0.537

-0.274

18:3n-6

0.05

Nd

0.04

0.05

0.05

0.05

0.06+0.00

0.06+0.01

0.06+0.02

 

 

20:2n-6

2.48

0.13

1.21

0.24

0.68

0.88

0.89+0.06c

1.54+0.12a

1.11+0.04b

 

 

20:3n-6

0.18

Nd

0.20

0.25

0.21

0.13

0.09+0.01

0.07+0.03

0.08+0.02

 

 

20:4n-6

0.02

Nd

0.06

0.03

0.05

0.86

0.13+0.03

0.14+0.01

0.13+0.01

0.945

-0.357

PUFAs n-6 (others)

1.08

Nd

0.95

0.55

0.73

0.77

1.02

0.85

0.95

 

 

PUFAs n-6

4.18

0.50

2.88

1.51

2.32

3.40

2.60+0.24b

3.18+0.23a

2.75+0.02b

0.986

-0.431

18:3n-3

2.07

51.36

4.58

21.93

12.64

4.27

1.94+0.07c

19.35+0.40a

10.60+0.07b

0.999

1.001

18:4n-3

0.32

Nd

0.60

0.71

0.84

2.61

1.04+0.04

1.01+0.03

1.09+0.06

 

 

20:3n-3

0.05

Nd

0.61

0.05

0.05

0.53

0.30+0.03

0.31+0.04

0.30+0.01

 

 

20:5n-3

5.90

Nd

2.95

0.73

1.69

0.87

2.08+0.10a

0.92+0.05c

1.47+0.01b

0.999

0.521

22:6n-3

12.82

Nd

6.65

2.16

4.05

4.76

10.73+0.40a

5.72+0.39c

8.60+0.18b

0.984

1.098

PUFAs n-3 (others)

0.48

Nd

0.36

0.22

0.28

0.25

0.59

0.26

0.46

 

 

PUFAs n-3

21.62

51.36

15.75

25.80

19.55

13.28

16.67+0.52c

27.57+0.72a

22.51+0.22b

0.978

1.035

HUFAs n-3

18.72

Nd

9.60

2.89

5.74

5.63

12.80+0.45a

6.64+0.42c

10.07+0.19b

 

 

PUFAs

 

 

 

 

 

16.68

19.27+0.66c

30.75+0.57a

25.26+0.24b

0.982

1.287

PUFAs/SFAs

 

 

 

 

 

0.90

0.69+0.04c

1.41+0.02a

1.04+0.02b

 

 

n-6/n-3

 

 

 

 

 

0.26

0.16+0.02a

0.12+0.01b

0.12+0.00b

 

 

nd: not detected, FOD: fish oil diet, FxOD: flaxseed oil diet, FFxOD: fish and flaxseed oils diet. Values in the same row with the same superscripts are not significantly different (P>0.05).

Oils

Initial

FOD

FxOD

FFxOD

FOD

FxOD

FFxOD

However, DHA was found in high concentrations within all of the dietary treatments, ranging from 5.7+0. 4% (FxOD) to 10.7+0.4% (FOD). The level of n-3 fatty acids was higher in the fillet than the diet for each of the treatments, but the level of n-6 fatty acids was higher in the fillet than the diet only for FxOD and FFxOD, with n-6/n-3 ratios ranging from 0.12+0.00 to 0.16+0.02 in the fillet. The highest HUFAs n-3 concentrations (P<0.05) were found in fish fed the FOD (12.8+0. 4%), while the lowest value was observed in fish fed the FxOD (6.6+0.4%).

Regression analysis was used to identify dose response relationship between dietary and fillet fatty acids. Most of the fatty acid concentrations in the fillet were linearly correlated to the dietary fatty acids concentrations.

Discussion and Conclusion

The results of the present study suggest that flaxseed oil can be used to replace fish oil without adverse effects on nutritional value of fish for human consumption. In agreement with previous studies [7, 11, 23, 31], considerable differences were evident in the fatty acids composition of fish fed different lipid sources. For example, there was a high increase in the levels of a-linolenic acid in fish fed either with FxOD and/or FFxOD. As reported by other researchers [5, 12, 29, 30, 31], a high correlations are also exist between the individual fatty acids as well as MUFAs and PUFAs of a diet and the fish fillet. There was, however, a high correlation between the amount of SFAs in the diet and SFAs in the fillet, which was not in accordance with the findings of Turchini et al., (2003a, b) [30, 31] who postulated that SFAs were not used efficiently by Murray cod (Maccullochella peelii peelii) as an energy source and were subsequently deposited at an optimal level in preference to the other major fatty acid classes. It is well known that freshwater fish have a dietary requirement for n-3 and n-6 fatty acids, predominantly in the form of a-linolenic and linoleic acids [12, 16, 19, 20, 23, 28]. In comparison to marine fish species, freshwater fish are also generally better adapted to desaturate and elongate these base fatty acids to higher

homologs [12, 28]. This study observed a-linolenic acid in lower concentrations in the muscle than in the diets. It is therefore suspected that a high degree of metabolism of this fatty acid for p-oxidation and/or desaturation and elongation is taking place in fishes in this experiment. This is further bolstered by the presence of n-3 desaturation and elongation enzyme products in the form of 18:4n-3 and 20:3n-3 in fish fed FxOD and FFxOD. These fatty acids were found in much lower concentrations in the diets. Likewise, fish fed the FxOD and FFxOD contained n-6 desaturation and elongation intermediates (18:3n-6 and 20:3n-6) and indicate an elongation and desaturation of linoleic acid via A6 desaturase. However, further desaturation of 20:3n-6 to 20:4n-6 and 20:3n-3 to EPA and ultimately DHA was shrouded by high concentrations of these fatty acids within the fillet of initial fish samples. The Department of Health of England (HMSO, 1994) recommends a minimum PUFAs/SFAs ratio of 0.45, and a maximum n-6/n-3 of 4.0. Table 1 shows that our fish in all treatments met the PUFAs/SFAs and n-6/n-3 ratios. Despite the decrease in EPA and DHA in fillet from fish fed FFxOD, the trout fillets contained a relatively rich source of these fatty acids (584 mg of EPA plus DHA) with a 200 g serving portion of the fillets from fish fed FFxOD. This meets the intake of 500 mg day-1 of EPA plus DHA recommended by the International Society for the Study of Fatty Acids and Lipids [26].

Present study showed the substitution of fish oil with flaxseed oil in the rainbow trout diet have been possible without any negative effects on nutritional value of fish for human consumption. However, the reflection of the dietary oil source on the fillet fatty acid composition of the fish could be a potential drawback for vegetable oil substitution from a human nutritional point of view, given the decreases in levels of EPA and DHA in fish fed the vegetable oil diets. Further investigation into the benefits of other vegetable oils or indeed a blend of various vegetable oils is required in order to reduce usage of traditionally used fish oils, while simultaneously avoiding a reduction in the human health protective properties found within fish flesh.

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Effect of carbohydrate levels on growth and digestive enzymes in Caspian Kutum (Rutilus frissi kutum)

fingerlings

Sedigheh Mohmmadzadeh1, Bahrain Falahatkar1*, Hossein Ouraji2, Hamid Noverian1

1Fisheries Department, Faculty of Natural Resources, University of Guilan, Sowmeh

Sara, Guilan, Iran. falahatkar@guilan.ac.ir 2Sari Agricultural Sciences and Natural Resources University, Sari, Mazandaran, Iran

Introduction

Kutum (Rutilus frissi kutum) is an endemic fish and an important commercial species in Iran (Dorafshan, 2006). However no dietary requirement for carbohydrate has been demonstrated in this fish. Carbohydrates are the cheapest sources of food energy, but they are not well utilized by the animals (Aroeckuaraj et al, 2008). For establish the balanced diet and food requirement in the aquatics we need to understand the physiological function of digestive tract. Studies on the digestive secretions in fish can elucidate certain aspects of their nutritive physiology and resolve some nutritional problems, such as matching of an artificial diet to the nutritional needs of the fish. There are no enough information on the dietary carbohydrate requirements and digestive enzyme activity of Kutum. Therefore, the present study was designed to evaluate the effect of dietary carbohydrate levels in a practical diet on growth rate and changes in digestive enzymes activity of Kutum fingerlings.

Materials and methods

Five isoenergetic diets were formulated to continue graded levels of carbohydrate from 15 to 35%. The feeding experiments were conducted for a period of 10 weeks beginning in September 2011. All fish with an average weight of 0.8 ± 0.2 g were held in 15 aquaria (70- l) for 70 days at 23.5 ± 1°C. Each tank contained 30 fish with three replications per dietary treatment. Fish were fed according to their appetite four times per

day. The body weight of each fish was measured at the beginning and every 2 weeks interval and growth performance was calculated. At the end of the experiment, 9 fish from each tank were randomly sampled. The total set digestive was removed and frozen in the liquid nitrogen and conserved at 80°C for enzyme assays. Trypsin was assayed based on Erlanger et al (1961). a-amylase activity was determined by the 3, 5-dinitrosalicylic acid (DNS) methods (Bernfeld, 1951; Wortington, 1991) and lipase activity quantification followed according to the method by Iijima et al (1998). Data were subjeced to one-way ANOVA. Multiple comparisons among means between individul treatmnets were made with Tukeys test. The significance level was considered at p<0.05. All statistical analyses were preformed using SPSS 16.

Results

Growth performance and feed utilization of Kutum fingerlings fed by different dietary carbohydrate levels are shown in Table 1. After 10 weeks, significant differences were observed in final weight, weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER), among the treatments, but not for food conversion ratio (FCR). Trypsin, lipase and a-amylase specific activities changed significantly (p<0.05) by carbohydrate levels (Table 2). Those increased with increasing carbohydrate levels from 15 to 35%.

Table 1. Growth performance of Kutum (Rutilus frissi kutum) fed with different levels of carbohydrate for 10 weeks.

Dietary carbohydrate level (%)

15 20 25 30 35

Final weight (g)

1.7 ± 0.3 c

1.9 ± 0.4 c

1.9 ± 0.2 c

2.1 ± 0.3 b

2.3 ± 0.4 a

WG (g)

0.9 ± 0.3 d

1.1 ± 0.4 c

1.1 ± 0.2 c

1.3 ± 0.3 b

1.5 ± 0.4 a

SGR (% / day)

1.2 ± 0.3 d

1.4 ± 0.4 °d

1.5 ± 0.1 c

1.6 ± 0.3 b

1.7 ± 0.3 a

PER (%)

1.0 ± 0.4 c

1.1 ± 0.4 bc

1.1 ± 0.2 bc

1.2 ± 0.3 ab

1.3 ± 0.5 a

FCR

2.1 ± 0.2

2.4 ± 0.4

2.4 ± 0.3

2.1 ± 0.1

2.0 ± 0.1

Survival (%)

94.3 ± 1

94.4 ± 2.9

95.4 ± 2.9

97.7 ± 2.2

100

Table 2. Specific activity (U mg protein-1) of trypsin, lipase and a-amylase of Kutum (Rutilus frissi kutum) fed with different levels of carbohydrate for 10 weeks.

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