Effects of dietary replacement of fish oil by conjugated linoleic acid on some meat quality traits of Pacific white shrimp Litopenaeus vannamei

Food Chemistry 127 (2011) 1739–1743

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Effects of dietary replacement of fish oil by conjugated linoleic acid on some meat quality traits of Pacific white shrimp Litopenaeus vannamei Weijing Zhong, Shengpeng Zhang, Jinfeng Li, Weipei Huang, Anli Wang ⇑ Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, PR China

a r t i c l e

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Article history: Received 18 May 2010 Received in revised form 16 November 2010 Accepted 13 February 2011 Available online 17 February 2011 Keywords: Conjugated linoleic acid Litopenaeus vannamei Replacement Meat quality traits Fatty acid composition

a b s t r a c t This experiment was conducted to evaluate the effects of fish oil replacement by conjugated linoleic acid (CLA) on body proximate analysis and thiobarbituric acid-reactive substances, fat content, shear force and fatty acid composition in musculature of Pacific white shrimp (Litopenaeus vannamei). Graded levels of CLA (0%, 0.5%, 1% and 2%) were added to the basic diet of shrimp at the expense of fish oil. Results showed that fat content (p = 0.036) and shear force (p = 0.001) in shrimp musculature were enhanced with increasing dietary CLA inclusion. Fish oil replacement by CLA significantly promoted the incorporation of cis-9, trans-11 CLA (p = 0.0001) and trans-10, cis-12 CLA (p < 0.0001) into shrimp musculature; moreover, the polyunsaturated fatty acid was elevated (p = 0.020) and monounsaturated fatty acid was reduced by CLA inclusion (p = 0.024). It was concluded that replacement of fish oil by CLA could improve some meat quality traits of shrimp and 1% CLA was an appropriate amount. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Fish oil is widely applied in formulated aquaculture feeds, owing to its effective supply of energy and essential fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Sargent, Tocher, & Bell, 2002). Though it may be indispensable in shrimp diets, its limiting supply and high cost, concomitant with the possible accumulation of dioxins and dioxins-like polychlorinated biphenyls have made more and more industries seek alternative aquaculture feeds (Lundebye et al., 2004; Zhou, Li, Liu, Chi, & Yang, 2007). Different animal and vegetable oil sources had been used in shrimp diets to perform nutritional evaluation (Deering, Fielder, & Hewitt, 1997; Lim, Ako, Brown, & Hahn, 1997; Zhou et al., 2007). Soybean oil and corn oil, both rich in linoleic acid (18:2 n 6), have been introduced to partially replace fish oil in L. vannamei (Zhou et al., 2007) and Macrobrachium rosenbergii (Kamarudin & Roustaian, 2002) respectively. Nutritional evaluation, such as growth and fatty acid requirement, is very important for shrimp breeding; however the meat quality status is especially of importance to consumers after fish oil replacement. To date, there is little information about the investigation of meat quality status after different oil sources replacing fish oil.

⇑ Corresponding author. Tel./fax: +86 20 85210141. E-mail address: [email protected] (A. Wang). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.02.050

Previous studies indicated that fish oil containing highly unsaturated fatty acids (HUFA, such as EPA and DHA) has beneficial health functions in animal model and human (Charnock, 1994; Daviglus, 1997; Kromhout, Feskens, & Bowles, 1995). However, the quantity of HUFA in the shrimp body is reduced after replacing fish oil by terrestrial oil sources in diets, leading to more accumulation of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA, such as 18:2 n 6 and 18:3 n 3) (Lim et al., 1997). Compared to HUFA, these fatty acids, especially SFA and MUFA, have a lower cholesterol-reducing ability, potentially increasing the prevalence of coronary heart disease in humans (Williams, 2000). In addition, due to lower digestibility of these fatty acids compared to HUFA (Glencross, Smith, & Thomas, 2002), the lipid metabolism of the shrimp body was affected. Finally, the body proximate composition changed with reduced body lipid in L. vannamei (Lim et al., 1997; Zhou et al., 2007) and Penaeus monodon (Catacutan, 1991). Furthermore, some studies also demonstrated that musculature fat content was reduced by total replacement of HUFA by linoleic acid (LA) or linolenic acid in L. vannamei (González-Félix, Gatlin III, Lawrence, & Perez-Velazquez, 2003a, 2003b), although 50% replacement of fish oil by vegetable oil (linseed, soybean or corn oil) had no effect on musculature fat content (Ouraji et al., 2009). All of these results showed that HUFA in shrimp diets had the tendency to increase body or muscle lipid content. Though HUFA is beneficial to humans, it is susceptible to peroxidation, leading to rancidity and harmful reaction products in shrimp feeds (Nirmal & Benjakul,

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2009; Williams, 2000). Thiobarbituric acid-reactive substances (TBARS) assay is commonly used to estimate the extent of lipid peroxidation, and then the deterioration of lipids in seafood (Ersoy, Aksan, & Özeren, 2008; Jiang, Feng, et al., 2010; Ouraji et al., 2009). It is well known that lipid peroxidation can catalyse protein oxidation to negatively affect the shear force of fresh meat (Bhor, Raghuram, & Sivakami, 2004; Rowe, Maddock, Lonergan, & Huff-Lonergan, 2004). Therefore, shear force is another important quality trait for shrimp meat (Pornrat, Sumate, Rommanee, Sumolaya, & Kerr, 2007). It is also suggested that shear force (meat firmness) can be affected by muscle SFA in pig (Wiegand, Parrish, Swan, Larsen, & Baas, 2001). According to the above information, these meat quality traits are correlated with variance of fatty acid composition in shrimp meat. Shrimp meat fatty acid composition could be easily changed by diets containing different lipids (Deering et al., 1997; Lim et al., 1997; Zhou et al., 2007). Hence, it can be deduced that meat quality status of shrimp will be changed after changing lipid composition in diets. It is also feasible that improvement of some of these meat quality traits may be achieved by selecting an efficacious oil source to replace fish oil. Conjugated linoleic acid (CLA) is a group of geometric and positional isomers of LA (18:2 n 6) with conjugated double bonds. Previous studies have demonstrated that CLA as a dietary supplement has a potent ability to improve some meat quality traits (such as enhancing intramuscular fat content, shear force and CLA incorporation into tissues, reducing TBARS and changing fatty acid composition) in pigs (Jiang, Zhong, et al., 2010; Sun, Zhu, Qiao, Fan, & Li, 2004; Wiegand, Parrish, Swan, Larsen, & Baas, 2001), chickens (Szymczyk, Pisulewski, Szczurek, & Hanczakowski, 2001) and fish (Berge, Ruvter, & Åsgård, 2004; Valente et al., 2007). Dietary inclusion of CLA can also promote the deposition of CLA isomers in meat (Bandarra et al., 2006; Jiang, Zhong, et al., 2010; Szymczyk et al., 2001). CLA has been reported to possess health benefits, such as anti-obesity (Gaullier et al., 2005), anti-tumour (Kim, Hubbard, Ziboh, & Erickson, 2005) and others. Consequently, these CLA-rich products are healthy foods for consumers. Pacific white shrimp, Litopenaeus vannamei, is one of the main cultivated species in China. Due to its delicacy and excellent nutrient composition, L. vannamei is extensively accepted by consumers (Sriket, Benjakul, Visessanguan, & Kijroongrojana, 2007a). The objective of this experiment was to investigate the effects of dietary CLA replacing fish oil on meat quality traits in L. vannamei, including body proximate analysis, intramuscular fat content, TBARS, shear force and fatty acid composition.

at 20 °C until use. Each diet was randomly assigned to one treatment with four barrels and each barrel was stocked with 35 shrimps. During the experiment, water temperature was kept at 30 ± 2 °C, pH 7.9–8.1 and salinity 6–7‰ with constant oxygenation. Uneaten food and excreta were removed every 3 days. Shrimps were fed 3 times each day at 8:00, 14:00 and 21:00 h for 8 weeks.

2. Materials and methods

2.3. Sampling preparation

2.1. Shrimps

After the 8-week feeding, shrimps were fasted and sampled. Two whole shrimps were taken from each barrel, the surface water was removed with filter paper, and the shrimps stored at 80 °C for body proximate analysis (crude protein, crude fat, ash and moisture). The musculature of four shrimps from each barrel without shells was obtained as one sample, frozen in liquid nitrogen immediately and stored at 80 °C for musculature fat content and fatty acid analysis. The musculature of three shrimps from each barrel without shells was obtained, frozen in liquid nitrogen immediately and stored at 80 °C for TBARS (one shrimp sample) and shear force (two shrimp samples) analysis.

The shrimps, L. vannamei, used in this study were purchased from a commercial farm (Tianyi village, Panyu district, Guangzhou, China). The shrimps (n = 1000) were acclimated for 2 weeks before experimentation. After acclimation, 560 shrimps (approximately 40 days-old) were selected, weighed (mean = 1.59 g) and grouped for further experimental work. 2.2. Experimental design and procedure The CLA (containing 80% CLA mixture) was purchased from Zhongshan Unicare Natural Medicine Co. Ltd. (Zhongshan, China). Graded levels (0%, 0.625%, 1.25% and 2.5%) of CLA oils were supplemented to a basal diet to formulate four experimental diets, with graded levels of pure CLA (0%, 0.5%, 1% and 2%) at the expense of fish oil (Table 1). The fatty acid compositions of the experimental diets are listed in Table 2. Diets were mixed, pelleted and stored

Table 1 Ingredients of experimental diets. Ingredient (%)

Control

0.5% CLA

1% CLA

2% CLA

Fish meal Soybean meal Flour Rapeseed meal Wheat bran Fish oil CLA Calcium hydrogen phosphate Salt Premixa

15 56 10 9 5.5 2.5 0 0.6 0.4 1

15 56 10 9 5.5 1.875 0.625 0.6 0.4 1

15 56 10 9 5.5 1.25 1.25 0.6 0.4 1

15 56 10 9 5.5 0 2.5 0.6 0.4 1

Chemical composition Crude protein Crude lipid Ash

40.49 5.37 7.91

40.37 5.53 7.89

40.65 5.17 8.05

40.76 5.01 7.94

a Mineral and vitamin mixtures were provided by Institute of Animal Science in Guangdong Academy of Agricultural Sciences in China.

Table 2 Fatty acid composition of experimental diets.a Fatty acids

Control

0.5% CLA

1% CLA

2% CLA

12:0 14:0 16:0 16:1 n 7 18:0 18:1 n 9 18:2 n 6 18:3 n 3 Cis-9, trans-11 CLA Trans-10, cis-12 CLA 20:0 20:4 n 6 20:5 n 3 22:5 n 3 22:6 n 3 Others

0.10 3.33 16.09 4.08 3.39 18.20 24.80 3.33 0.46 0.38 0.19 0.20 6.73 1.70 3.78 13.24

0.07 2.85 15.26 3.49 3.25 16.24 22.40 3.03 4.26 4.56 0.44 0.15 6.21 1.47 3.25 13.05

0.05 2.37 14.27 2.90 3.12 14.71 19.55 2.64 8.63 9.33 0.72 0.12 5.47 1.24 2.71 12.17

–b 1.36 12.34 1.64 2.83 10.95 13.97 1.92 17.32 18.84 1.29 0.02 4.14 0.74 1.56 11.09

a Values were presented as relative percentage of all measured fatty acids (g/ 100 g fatty acids). b –; not detected.

2.4. Sample analysis The samples used for the analysis of ash, crude fat, crude protein, musculature fat content and fatty acid composition were minced and freeze-dried to form the sample powder.

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2.4.1. Proximate analysis Two shrimps were analysed for moisture (drying in an oven at 105 °C for 24 h), ash (incineration in a muffle furnace at 550 °C for 4 h), crude fat (Soxtec 2055 fat extraction system, Foss Tecator AB, Hönganäs, Sweden) and crude protein (Kjeltec 2300 Autoanalyser, Foss Tecator AB). The content of fat content in musculature was also determined, using petroleum ether extraction after Soxtec 2055 fat extraction. 2.4.2. Fatty acid analysis Total lipids were extracted according to the method of Folch and Sloane-Stanley (1957) and the fatty acids were methylated using the standard method for determination of DHA and EPA contents from milk powder and formula foods for infant and young children in China (GB/T 5413.27-1997). The fatty acid methyl esters (FAME) were analysed on a gas chromatograph (Thermo Finnigan Co., San Jose, CA) equipped with a capillary column (30 m  0.32 mm). The initial oven temperature of the gas chromatograph was set at 120 °C for 1 min, increased to 200 °C at a rate of 25 °C /min for 3 min and then increased to the final temperature of 230 °C at a rate of 2 °C/min for 8 min. The injector and detector temperature were set at 270 °C. The FAME (1 ll) were injected into the split injection port (30:1 split ratio). The flow rate of helium carrier gas was 1.5 ml/min. The FAME were identified by comparison of their retention times with those of corresponding standards. Individual FAMEs were quantified as the percentage of a specific peak area relative to the total FAME peak areas. 2.4.3. Determination of TBARS The TBARS values from shrimp musculature were determined according to our previous method (Jiang, Zhong, et al., 2010), using a malondialdehyde (MDA) kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). The MDA in musculature can combine with the thiobarbituric acid to form red products which had the greatest absorbance at 532 nm. The results were expressed as nmol (MDA) per milligram protein. 2.4.4. Shear force analysis The shear force of shrimp musculature was examined with an INSTRON 4411 Materials Testing Instrument (Instron Corporation, Canton, MA). The operating parameters included a cross-head speed of 10 mm/s and a 10-kg load cell. The muscles of shrimps were thawed at room temperature and then cooked by steam until the internal temperature attained 70 °C. After cooking, samples were cooled in iced-water and applied to the INSTRON testing apparatus for shear force analysis. The shear force values for individual prawns were presented according to the procedure of Pornrat et al. (2007). 2.5. Statistical analysis All data were analysed with one-way ANOVA of SAS 8.1 (SAS Inst. Inc., Cary, NC). Differences among means were identified using Duncan’s multiple-range test. A probability of less than 0.05 was considered significant (p < 0.05). 3. Results and discussion Dietary CLA replacing fish oil had no significant effect on crude protein, crude fat nor ash of whole shrimp (P > 0.05; Table 3), while shrimps that consumed the diet with 0.5% CLA had significantly higher moisture than those with 1% CLA and the control (p < 0.05). The marked enhancement of moisture in L. vannamei by 0.5% CLA replacing fish oil should be at the expense of other nutrients, resulting in lower crude protein and crude fat. However,

Table 3 Proximate analysis of whole shrimp.*

Crude protein Crude fat Ash Moisture

Control

0.5% CLA

1% CLA

2% CLA

SEM

p-value

17.19 0.68 3.13 75.55b

16.37 0.44 3.02 77.07a

17.29 0.65 2.77 75.54b

16.34 0.60 3.08 76.34ab

0.32 0.09 0.13 0.44

0.068 0.289 0.281 0.081

* All data were presented as means of four shrimps and shown as % of wet weight. Different letters within the same line differ significantly (p < 0.05).

this hypothesis was not true in the present study. To date, knowledge about the effects of fish oil replacement by CLA on shrimp body proximate composition are very scarce. It has only been shown that dietary CLA supplemented to fish diets had no significant effect on the whole body composition in fish such as hybrid striped bass (Twibell, Watkins, Rogers, & Brown, 2000), Atlantic salmon (Berge et al., 2004) and rainbow trout (Valente et al., 2007). The TBARS value of shrimp musculature was not significantly affected by CLA replacing fish oil and displayed 6.7–26.7% decline (Table 4). This reduction points to a slight improvement of TBARS value and, therefore, lipid peroxidation status. Shrimps fed the diet with 1% CLA replacing fish oil possessed significantly enhanced fat content in musculature, when compared with the control and 0.5% CLA groups (p < 0.05, Table 4), while 2% CLA replacing fish oil did not markedly change musculature fat content in comparison with the control. The mean value of muscle fat content in our present study varied from 0.42% to 0.55% of musculature. Shellfish are low in fat (Ackman, 1989) and the fat content in the edible parts is 0.5–1.5% (Ackman, 2000). From this information, it can be seen that the muscle fat content of our samples was very low. Intramuscular fat content in rabbit has a positive effect on tenderness, resulting in improved meat quality and consumer acceptability (Gondret, Juin, Mourot, & Bonnear, 1998). Hence, we hypothesise that the higher fat content in shrimp muscle induced by 1% CLA may be associated with better meat quality. Of course, this idea should be tested in a further experiment. Increased intramuscular fat content due to dietary CLA has been confirmed in pigs (Jiang, Zhong, et al., 2010; Sun et al., 2004; Wiegand et al., 2001) and rabbits (Gondret et al., 1998). Another notable finding in our experiment was that, unlike in shrimp muscle, fat content in the whole shrimp did not show any obvious changes, due to 1% CLA replacing fish oil. The difference may due to selective fat accumulation in musculature by dietary CLA. The shear force of shrimp musculature was significantly enhanced by 2% CLA replacing fish oil (p < 0.05, Table 4). The diets containing 0.5% and 1% CLA had no significant treatment effect on shear force compared with the control. Little is known about the effects of dietary CLA on shear force in shrimp and other aquatic animals. However, enhanced muscle shear forces in pigs were usually accompanied by dietary CLA supplementation (Jiang, Zhong, et al., 2010; Wiegand et al., 2001), which agreed with our present study. A reduction in shear force indicates damage of the integrity of muscle fibres (Sriket, Benjakul, Visessanguan, & Kijroongrojana, 2007b). In other words, the enhancement of shear force by dietary 2% CLA replacing fish oil may produce a better muscle composition to prevent the weakening of the muscle and extend shelf life. However, significantly high shear force also resulted in tough meat with poor acceptability. The enhancement of shear force by 2% CLA might be linked to increased collagen content (Sriket et al., 2007a) and saturated fat in tissues (Wiegand et al., 2001), but, according to our present results, the total SFA in musculature were not affected by CLA replacing fish oil. Thus, further studies should be done to confirm the relationship between collagen content and shear force. The fatty acids composition of musculature from L. vannamei is presented in Table 5. Replacement of fish oil by 2% CLA

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Table 4 Meat quality traits of L. vannamei fed graded levels of CLA.*

TBARS (nmol MDA/mg protein) Muscle fat content (% of wet weight) Shear force (N/cm) *

Control

0.5% CLA

1% CLA

2% CLA

SEM

p-value

0.15 0.42b 2.18b

0.14 0.44b 2.73b

0.13 0.55a 1.81b

0.11 0.46ab 7.27a

0.01 0.47 4.13

0.199 0.029 0.001

All data were presented as means of four shrimps. Different letters within the same line differ significantly (p < 0.05).

Table 5 Fatty acid composition of musculature in L. vannamei fed different levels of dietary CLA.* Fatty acids

Control

0.5% CLA

1% CLA

2% CLA

SEM

p-value

12:0 14:0 16:0 18:0 20:0 RSFA 16:1 n 7 18:1 n 9 RMUFA 18:2 n 6 Cis-9, trans-11 CLA Trans-10, cis-12 CLA 18:3 n 3 20:4 n 6 20:5 n 3 22:5 n 3 22:6 n 3 RPUFA** Rn 6 PUFA Rn 3 PUFA Others

0.10 0.32 21.52a 9.12 0.16b 31.22 0.93a 17.27a 18.19a 15.84 0.34d 0.07d

0.05 0.27 21.22a 9.43 0.62ab 31.59 0.83a 16.44ab 17.27ab 15.08 3.26c 1.09c

0.11 0.19 20.34ab 9.29 0.77a 30.7 0.58b 15.32bc 15.9bc 15.67 5.73b 2.14b

0.04 0.22 19.70b 9.28 0.99a 30.23 0.85a 14.53c 15.38c 15.17 8.41a 3.08a

0.04 0.04 0.45 0.23 0.16 0.51 0.07 0.50 0.55 0.46 0.63 0.21

0.495 0.108 0.071 0.828 0.037 0.316 0.037 0.021 0.024 0.597 0.0001 <0.0001

0.91 2.21 13.38a 0.90 9.72 43.38b 18.05 24.92a 7.21

0.96 2.14 11.98ab 0.84 8.41 43.76b 17.22 22.18ab 7.38

1.04 1.77 10.76ab 0.86 8.45 46.42ab 17.44 21.11ab 6.97

1.07 2.30 10.23b 0.71 8.31 49.29a 17.47 20.32b 5.10

0.06 0.27 0.80 0.09 0.58 1.12 0.30 1.30 1.01

0.277 0.556 0.092 0.460 0.332 0.020 0.327 0.146 0.403

*

All data were presented as means of three shrimps and shown as relative percentage with all measured fatty acids (g/100 g fatty acids). Different letters within the same line differ significantly (p < 0.05). ** Includes the content of cis-9, trans-11 CLA and trans-10, cis-12 CLA.

significantly decreased 16:0 content (p < 0.05). Furthermore, the content of 20:0 was markedly increased in response to 1% and 2% CLA inclusion (p < 0.05). However, total SFA detected were not changed, which was with the same as previous results in muscle of rainbow trout (Valente et al., 2007) and in liver of Atlantic salmon (Leaver et al., 2006). However, enhanced SFA appeared in muscle and liver tissues of rainbow trout (Bandarra et al., 2006; Valente et al., 2007) and in muscle and fat tissues of pigs (Jiang, Zhong, et al., 2010) and chickens (Szymczyk et al., 2001). By contrast, reduced SFA was shown in muscle of Atlantic salmon (Leaver et al., 2006). It is shown that SFA has a very low digestibility in crustaceans (Berge et al., 2004), which may result in excessive accumulation of 20:0 in L. vannamei due to dietary CLA. The reduced level of 16:0 in shrimps may reflect its use as an energy supply because lipid is the main energy source for crustacean growth and development (Phillips et al., 2006). Replacement of fish oil by 1% CLA significantly reduced 16:1 n 7 content, and 1% and 2% CLA groups decreased 18:1 n 9 content in shrimp musculature, which led to reduced MUFA in response to 1% and 2% CLA inclusion (p < 0.05). It has been demonstrated that dietary CLA could cause an inhibition of D9 desaturase activity in hybrid striped bass (Twibell et al., 2000) and Atlantic salmon (Berge et al., 2004), thereby reducing MUFA content in animal tissues. From these earlier reports, the depression of D9 desaturase activity may also be involved in the reduction of MUFA in our experiment. Nevertheless, such a decrease in MUFA level might be reflected by an increase in

the corresponding SFA content, but this was not the case in the current trial. Dietary 2% CLA replacing fish oil significantly decreased 20:5 n 3 content (p < 0.05). The 20:5 n 3 and 22:6 n 3 fatty acids are both essential for better shrimp growth and maximum survival (Lim et al., 1997). The reduction of 20:5 n 3 in L. vannamei due to 2% CLA inclusion, led to reduced growth performance (Table 6). Furthermore, 20:5 n 3 and 22:6 n 3 fatty acids are very important long chain x3 fatty acids with beneficial cardiovascular and anti-inflammatory properties (Williams, 2000). The deficiency of 20:5 n 3 in musculature reduced the health value of shrimp meat. Although L. vannamei has a dietary requirement for 18:2 n 6, its conversion to other polyenoic forms of longer chain length is limited (Lim et al., 1997). Therefore, a large amount of CLA deposited in musculature could not be converted to other PUFA, resulting in the reduction of 20:5 n 3. Enhanced PUFA in musculature was mainly derived from increased CLA isomers. This higher PUFA was also found in liver and muscle tissues of Atlantic salmon (Leaver et al., 2006) and rainbow trout (Bandarra et al., 2006). Dietary CLA significantly promoted cis-9, trans-11 CLA and trans-10, cis-12 CLA incorporation in musculature in a dosedependent manner (p < 0.05). Furthermore, cis-9, trans-11 CLA had more deposition than trans-10, cis-12 CLA, which was also confirmed by some earlier results in rainbow trout (Bandarra et al., 2006) and pigs (Jiang, Zhong, et al., 2010; Sun et al., 2004). The reason may come from preferable incorporation of cis-9, trans-11 CLA into musculature or better stability of cis-9, trans-11 CLA than trans-10, cis-12 CLA in musculature (Bandarra et al., 2006; Kelley, Bartolini, Newman, Vemuri, & Mackey, 2006). CLA deposition in aquatic fishes can provide functional foods for consumers (Bandarra et al., 2006; Berge et al., 2004). According to Bandarra et al. (2006), although the quantity of dietary CLA deposited in different fish species varied, it was still a higher amount than some other vertebrates. It was exciting to find that the CLA concentration deposited in shrimp musculature in our experiment (4.35– 11.49 g/100 g fatty acids) was greater than that had been reviewed (2.92–7.97 g/100 g fatty acids) by Bandarra et al. (2006), indicating that shrimp and fish are both potential sources of dietary CLA in humans.

Table 6 Growth performance of L. vannamei fed graded levels of dietary CLA.* Control

0.5% CLA 1% CLA

Initial weight (g) 1.60 1.59 Final weight (g) 5.82a 6.08a Weight gain (%)** 260.55 282.52 Specific growth 2.29ab 2.39a rate (%)*** 89.29ab Survival rate (%)**** 92.38a *

1.58 6.02a 280.55 2.38a 87.86ab

2% CLA

SEM

p-value

1.61 0.04 0.983 5.32b 0.13 0.0001 229.20 15.49 0.105 2.12b 0.08 0.098 82.14b

2.09 0.050

All data were presented as means of four replications for each treatment. Different letters within the same line differ significantly (p < 0.05). ** Weight gain, % = 100  [(final weight initial weight)/(initial weight)]. *** Specific growth rate, % = 100  [(average final weight average initial weight)/ feeding period, day]. **** Survival rate, % = 100  (number of shrimps at the end of the experiment)/ (number of shrimps at the beginning of the experiment).

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