Combined effects of dietary phosphatidylcholine and cholesterol on the growth, survival and body lipid composition of marine shrimp, Penaeus penicillatus

167

Aquaculture, 96 ( 1991) 167- I 78 Elsevier Science Publishers B.V.,Amsterdam

Combined effects of dietary phosphatidylcholine and cholesterol on the growth, survival and body lipid composition of marine shrimp, Penaeus penicillatus Houng-Yung Chen and Jan-Shyong Jenn’ Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan (Republic of China) (Accepted 30 December 1990)

ABSTRACT Chen, H.Y. and Jenn, J.S., 199 1. Combined effects of dietary phosphatidylcholine and cholesterol on the growth, survival and body lipid composition of marine shrimp, Penaeuspenicillatus. Aquaculture, 96: 167-178. A factorial experiment with four dietary phosphatidylcholine (0, 1.25,2.5 and 5%) and three cholesterol (0.0.5 and 1%) levels was carried out usingjuvenile Penaeuspenicillatus with an initial mean body weight of 1 g. The trial was conducted for only 4 weeks using purified diets. The results indicated that diets supplemented with either phosphatidylcholine or cholesterol significantly improved shrimp weight gain. Supplementary cholesterol, but not phosphatidylcholine, significantly improved shrimp food conversion and survival. The interactions between phosphatidylcholine and cholesterol on shrimp growth, food conversion and survival were not significant. The dietary cholesterol level to achieve significant shrimp growth was 0.5% or higher, while that for phosphatidylcholine was 1.25Ohor higher. The inclusion of cholesterol in the purified diets affected lipid deposition. The shrimp muscle lipid content increased with the increased supplement of cholesterol or phosphatidylcholine. The lipid class composition, however, was not influenced by the two dietary components. Both the n3/n6 ratios of the fatty acids and the n3-PUFA level in the polar fraction of the muscle tissue lipid increased with reduced dietary phosphatidylcholine. The n6 fatty acids derived from the soy phosphatidylcholine were accumulated and preferentially incorporated into the polar lipid of the muscle tissue.

INTRODUCTION

Dietary cholesterol and phospholipids are known to promote growth and survival of many crustacean species (Kanazawa, 1982; D’Abramo et al., 1985; Kean et al., 1985). Many shrimp species have been shown incapable of de novo synthesis of sterols. The dietary cholesterol requirement ranges from 0.1 ‘Present address: Agricultural Animal Products Division, 137. Sec. 2 Nanking East Road, Taipei, Taiwan, ROC.

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H.Y. CHENAND J.S. JENN

to 0.2% (Shudo et al., 1971) and 0.5% (Teshima et al., 1983) to 1.4% (Deshimaru and Kuroki, 1974) for Penaeus japonicus and from 0.12 to 0.5% for juvenile Homarus lobster (Bordner et al., 1986). The absolute requirements of Penaeus penicillatus for cholesterol have not been reported. Dietary supplementation of phospholipids, such as soybean lecithin, at levels between 0.5 and 8% of the diet has proved essential in casein-based purified diets (Briggs et al., 1988). D’Abramo et al. ( 1982) demonstrated that phosphatidylcholine is the active ingredient in the soy lecithin. Kanazawa et al. ( 1985) indicated that among the many phospholipids tested, soy phosphatidylcholine and phosphatidylinositol as well as phosphatidylcholine derived from bonito eggs are more effective in promoting larval P. japonicus growth and survival. Due to the availability and the cost of purified phospholipids, most of the data published so far used low purity phospholipid sources. The inconsistency of the lipid quality has made the comparison between different studies difficult. Lester et al. ( 1975 ) have shown that lecithin-enhanced cholesterol solubilization was affected by N- (N-dodecanoylsarcosyl) taurine. The transport of lecithin in shrimp body fluid was closely related to the phospholipids of high density lipoprotein (Teshima et al., 1986). The cholesterol-lecithin interaction was, thus, speculated. Kean et al. ( 1985) indicated in a growth study with the juvenile lobster (Homarus americanus), that the interaction is not significant. The possibility of enhanced cholesterol availability due to dietary lecithin is still not clear. The purpose of the present study was to investigate the growth promoting effects of dietary cholesterol and phosphatidylcholine in combination. The effects on the shrimp body lipid composition were also investigated. MATERIALS AND METHODS

Juvenile P. penicillatus for the experiment were obtained from outdoor ponds of a local commercial shrimp farm. The juveniles were then maintained in aquaria with a density of 60 animals per m* and were fed a commercial compounded diet for 1 week. Prior to stocking into the 60W x 60L x 46.5H cm experimental aquaria, the animals were weighed and ranked so that tank biomasses were generally similar. For each dietary treatment, 36 juveniles, divided into two groups of 18, were used. Each separate group was housed in an aquarium. The aquaria were fitted with under-gravel filters. The filter bed consisted of crushed oyster shell and sand. Salinity was maintained at 30 ppt. Temperature was not controlled but monitored. The mean water temperature ranged between 23.6-26.2”C. The composition of the basal diet is shown in Table 1. Test diets 1- 12 contained different levels and combinations of soy phosphatidylcholine and cholesterol. Phosphatidylcholine was purified chromatographically from soy lec-

EFFECTS OF DIETARY PHOSPHATIDYLCHOLINE

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169

TABLE I Composition

of the basal diet

Ingredients

O/oDry diet

Ingredients

% Dry diet

Casein Dextrin Amino acid mixturea Glucosamine HCl Sodium succinate Cellulose

45.1 20.0 3.0 0.8 0.3 4.2

Vitamin mixb Mineral mix’ Sodium alginate Sodium hexametaphosphate Fish oild Soybean oil’

2.6 8.6 2.5 1.0 5.0 O-6

“Alanine: glycine : glutamic acid: betaine = 1: 1: 1 : 2 (as attractant ). ‘In mg/ 100 g of dry diet: p-aminobenzoic acid, 10; biotin, 0.4; inositol, 400; nicotinic acid, 40; Capantothenate, 60; pyridoxine hydrochloride, 12; riboflavin, 8; thiamin hydrochloride, 4; menadione, 4; p-carotene, 9.6; a-tocopherol, 20; vitamin B-12,0.08; calciferol, 1.2; sodium ascorbate, 2000; folic acid, 0.8; choline chloride, 120. ‘In g/ 100 g of diet: K2HP04, 2.0; Ca,( Pod)*, 2.72; MgS0,*7H20, 3.04; NaHzP04*2Hz0, 0.79. “Contains 0.88% cholesterol. ‘Levels adjusted to compensate for various addition of cholesterol and phosphatidylcholine.

ithin in the Food Science and Nutrition Department of the Fu-Jen Catholic University, Taipei. TLC/FID analysis indicated that the phosphatidylcholine contained 80% phosphatidylcholine and 20% lyso-phosphatidylcholine. All diets were rendered isocaloric by varying the soybean oil from O-6% depending on the amounts of phosphatidylcholine and cholesterol added to the various diets. Fish oil (5%) which contained 0.88% cholesterol was added so as to supply essential n3 polyunsaturated fatty acids, the requirement of which is suggested to be 1% of the diet (Kanazawa, 1982). The cholesterol in the fish oil resulted in the additional inclusion of 0.044% cholesterol to each test diet. The fatty acid compositions of phosphatidylcholine, soybean oil and fish oil are listed in Table 2. Measured ingredients were thoroughly blended for at least 15 min in a mixer. Alginate and sodium hexametaphosphate were dissolved and stirred in 7580°C warm water. Colloid liquid was then added to the dry components to form a stiff dough. The dough was then hard-extruded as 2 mm diameter spaghetti-like strands and freeze-dried. Dried strands were broken into 5 mm pellets and stored in plastic bags at - 20 oC. The lipids in the soy phosphatidylcholine, the fish oil and the shrimp body were extracted by the Folch method (Christie, 1982). Both the muscle and hepatopancreas of the test shrimp were sampled at the end of the growth trial for lipid analysis. The quantification of total lipids was based on the method of Kates ( 1972). The neutral and polar fractions of the extracted lipids were separated by chloroform and methanol elution of a silicic acid ( 100 mesh, Sigma) chromatographic column (Rouser et al., 1967). The lipid components were then converted to fatty acid methyl esters. A HP5890A gas chro-

170

H.Y. CHEN AND J.S. JENN

TABLE 2 Fatty acid compositions in the trial

(% of total fatty acids) of phosphatidylcholine,

Fatty acid

Phosphatidylcholine

14:o 16:0 16: ln9 18:O 18: ln9 18:2n6 l8:3n3 20: ln9 20:4n6 20: 5n3 22: ln9 22:6n3

_ 16.12 _ 4.65 9.41 62.95 6.88 -

Total Total Total Total

6.88 62.95 9.41 20.77

n3 n6 n9 saturated

Soybean oil

9.73 2.61 20.91 56.60 10.42

_ 10.42 56.60 20.91 12.34

soybean oil and fish oil used

Fish oil 5.53 9.64 10.32 1.82 17.46 1.48 0.89 11.08 0.48 11.44 5.50 11.67 23.96 1.96 44.41 16.99

matograph with a 15-m long, 0.25 mm i.d. fused silica column (WCOT) employing a flame ionization detector was used to separate the methyl esters of the fatty acids. The column was packed with SP-2330 (Supelco) and operated isothermally at 190°C. The injector temperature was set at 220°C and the detector temperature at 220°C. Nitrogen, at a flow rate of 60 ml/min, was used as the carrier gas. The lipids were analyzed using a TLC/FID analyzer Mark IV (Iatron Co., Tokyo; Japan) according to the method of Fraser et al. ( 1985). The separation of lipid classes was performed on Chromarods II. The lipid extract samples were spotted on the rods in volumes of 0.1 ~1 and developed with chloroform/methane/water( 70/35/3.5, v/v) for the separation of polar lipids and hexane/ether/formic acid (85/l 5/0.04, v/v) for neutral lipids. A Shimazu CR-3A integrator attached to both chromatographs was used for quantification of the analyses. The results of total lipid content and lipid class composition analysis are expressed as weight percent of total fatty acids or total lipid and are the means of two and ten repeated analyses, respectively. The juvenile shrimps were fed to excess three times daily at approximately 09.00, 15.00 and 21.00 h. Uneaten food, fecal waste and molt exuvia were removed daily before each feeding. The waste feed was not measured to account into calculation of FCR. Shrimp were not weighed during the trial to prevent mortality. The dietary trial was conducted for 4 weeks. The shrimp were weighed individually to the nearest 0.01 g and the hepatopancreas and muscle tissues were sampled and frozen in liquid nitrogen for lipid analysis.

EFFECTS OF DIETARY PHOSPHATIDYLCHOLINE

AND CHOLESTEROL

ON MARINE SHRIMP

171

Statistical analyses were done using an ANOVA program from Statistical Analysis System (SAS ). RESULTS

Dietary supplementation of cholesterol (PC 0.0 1) or soy phosphatidylcholine (PcO.05) significantly improved P. penicillutus growth (Table 3). Shrimp fed diets with no supplement of either cholesterol or phosphatidylcholine, or both (but these diets still contained 0.044% cholesterol from fish oil) showed considerable growth during the 4-week trial. There was no significant dose-dependent growth promoting effect when the cholesterol level was higher than 0.5% or when the phosphatidylcholine was higher than 1.25%. In addition to the grotih-enhancing effect, dietary cholesterol significantly improved feed conversion ratio (Table 4) and survival (Table 5 ). Lower FCRs were observed (P-c 0.01) when more cholesterol was dispensed in the diet (Table 4). Fewer shrimp died during the growth trial with increased cholesterol level (P-c 0.05 ). The mean survival of shrimp increased significantly from about 70% in the absence of cholesterol to 84% when the diet contained 1.O%cholesterol. Unlike cholesterol, the contribution of phosphatidylcholine to FCR and survival (P> 0.05) was statistically insignificant. In addition, analysis of variance indicated that interactions on the shrimp weight gain, FCR and survival (P> 0.05 ) caused by cholesterol and phosphatidylcholine supplementation were not significant. Dietary cholesterol content affected the total lipid level in the muscle of the shrimp, but not the lipid class composition (Table 6). The lipid content of the shrimp tail muscle increased with the increase of dietary cholesterol. The shrimp muscle lipid class composition did not reflect the dietary lipid class composition (Table 6). The shrimp fed diets containing high level of choles-

TABLE 3 Effects of dietary phosphatidylcholine and cholesterol penicillatus fed test diets after 4 weeks growth Cholesterol (%) 0 0.5 1.0 Mean

Phosphatidylcholine

on percent weight gain of juvenile fenaeus

(%)

Mean

0

1.25

2.5

5

95.0* 19.8 118.0f 11.3 129.5 f 10.2

99.0f 11.3 142.5k21.9 174.5+ 14.8

92.5f 5.2 133.5+ 13.4 145.5 f 15.9

145.5+_ 12.1 139.Ok26.9 156.0* 12.6

114.2”*

138.7d

123.8*

*Means with the same superscript are not significantly different (P
146.8d

108.0”* 133.3b 151.4b

172

H.Y.CHENANDJ.S. JENN

TABLE 4 Effects of dietary phosphatidylcholine and cholesterol levels on food conversion venile Penaeus penicihtus fed test diets after 4 weeks growth Cholesterol (%) 0

0.5 1.0

Phosphatidylcholine

ratio (FCR) of ju-

(%)

Mean

0

1.25

2.5

5

4.19t 1.05 3.15kO.45 2.84kO.64

4.17kO.29 2.67 +0.33 2.17f0.19

4.46 f0.98 2.80f 0.29 2.6lkO.71

2.66 f0.04 2.81 kO.86 2.25 kO.09

3.39

3.29

3.00

Mean

3.87”* 2.86b 2.46b

2.57

*Means with the same superscript are not significantly different (PC 0.05 ).

TABLE 5 Effects of dietary phosphatidylcholine and cholesterol levels on survival (%) of juvenile Penaeuspenicillatus fed test diets after 4 weeks growth Cholesterol (Oh) 0

0.5 1.0 Mean

Phosphatidylcholine

(%)

Mean

0

1.25

2.5

5

72.2+ 0.0 72.2+ 15.7 77.8& 0.0

66.7fO.O 66.7kO.O 77.8kO.O

69.5? 19.6 72.2f 0.0 83.3? 15.7

72.2? 15.7 77.8f 7.5 97.22 4.0

74.1

70.4

75.0

82.5

70.2= 72.2” 84.0b

*Means with the same superscript are not significantly different (P< 0.05).

terol or phosphatidylcholine did not show high content of the two compounds in their muscle tissue. The ~23/n6 ratio of the fatty acids in the polar lipid fraction of the muscle tissue decreased when the dietary phosphatidylcholine level increased, and so did the n3 polyunsaturated fatty acids level (Table 7). The n3/n6 ratio and n3 polyunsaturated fatty acids content of the neutral lipid fraction cannot be related to the dietary lipid composition. There were no dose-dependent relationships between the lipid level and lipid class composition in the hepatopancreas and the dietary lipid composition (data are not shown ),

19.0 0.4 1.7 0.9 10.0

Neutral lipid Steryl ester Triglycerides Free fatty acids Sterols

0.75

81.0 27.3 44.5 9.2 -

0 0

1

Polar lipid Phosphatidylethanolamine Phosphatidylcholine Sphingomyelin Lysophosphatidylcholine

Total lipid

PC(%) CS(%)

Lipid

19.1 2.0 2.2 0.7 7.1

80.9 26.2 39.2 15.5

0.90

1.25 0

2

20.9 1.9 1.3 1.3 10.1

79.1 25.8 41.4 11.9

0.98

2.5 0

3

Muscle total lipid contents (%) and their percent distribution phatidylcholine (PC ) and cholesterol (CS)

TABLE 6

1.10

17.1 1.9 1.5 0.6 8.9

82.9 25.2 41.7 8.8 7.2

5 0

4

21.5 3.0 1.6 1.1 11.8

78.5 23.2 38.1 9.1 8.1

1.13

0 0.5

5

19.0 4.1 2.1 0.8 9.8

81.0 20.8 37.9 11.4 10.9

1.08

1.25 0.5

6

Diet

22.2 0.9 1.8 1.0 10.9

71.8 25.0 43.0 9.1 _

1.32

2.5 0.5

7

23.5 4.8 2.0 1.0 11.9

80.4 23.1 42.5 10.3

1.15

5 0.5

8

of lipid classes of P. penicillatus fed experimental

1.22

23.0 3.5 1.7 90.7 9.8

84.4 26.3 43.5 10.3

0 1

9

23.8 5.7 1.9 2.6 8.2

16.2 23.1 43.0 10.1

1.30

1.25 1

10

21.0 9.1 1.5 0.5 10.3

79.0 20.2 40.9 9.0 9.9

1.35

2.5 1

11

1.43

17.3 2.8 1.6 0.7 12.2

82.8 39.1 18.1 19.5 _

5 1

12

diets containing varied levels of phos-

174

TABLE

H.Y. CHEN AND J.S. JENN 7

Fatty acid composition and n3/n6 ratios of polar and neutral lipids from muscle tissue of P. penicillatus fed purified diets containing graded levels of phosphatidylcholine (PC) and cholesterol (CS) Fatty acid

Diet 7

1

2

3

4

5

6

PC(%) CS(%)

0 0

1.25 0

2.5 0

5 0

0 0.5

1.25 0.5

Polar lipids 14: 1 16:0 16: ln9 16:2n4 17:o 18:O 18: ln9 18:2n6 18:3n3 20: ln9 20:2n6 20:4n6 20: 5n3 22: ln9 22:5n3 22:6n3

1.89 13.16 1.64 5.93 3.47 9.12 14.48 12.86 0.92 2.12 1.29 2.38 13.96 _ 16.76

16.80 2.39 3.69 9.38 16.40 15.98 3.82 12.56 -

1.21 20.52 2.26 2.03 1.18 9.47 17.57 17.37 1.27 2.29 1.52 1.92 10.53 -

19.28 1.96 2.26 2.39 10.08 14.85 21.37 2.42 1.98 10.91 -

1.10 18.11 2.14 2.07 2.85 8.40 18.95 16.74 1.29 2.53 1.39 1.55 9.63 0.78

15.97

10.86

12.50

Total n3 f.a. Total n6 f.a. Total n9 f.a. Tota1saturatedf.a. n3 PUFA* n3fn6

31.64 16.54 18.25 25.75 30.72 1.91

28.53 15.98 22.62 26.18 28.53 1.79

22.66 20.80 22.13 31.16 21.39 1.09

9.79 4.34 0.52

2.25 1.36

5.83 1.82 0.69 3.41 5.86 5.86

Neutral lipids 12:o 14:o 14: 1 16:0 16: 1119 17:o 18:0 18: ln9 18:2n6 18:3n3 18:4 20:o 20: ln9 20:2n6 20:3 20:4n6 20: 5n3 22:o

8

9

10

11

12

2.5 0.5

5 0.5

0

I

1.25 1

2.5 1

5 1

1.03 18.49 2.15 1.91 1.77 8.75 18.43 18.38 1.38 2.61 1.49 1.59 9.56 _

20.10 2.34 1.59 9.40 19.15 21.64 1.77 2.98 _

25.36 3.10 1.89 7.62 18.77 24.99 2.01 3.02 6.39 _

22.43 2.86 9.24 21.99 18.87 2.99 9.77 _

21.63 2.58 9.06 21.91 20.60 3.36 9.26 _

20.99 2.46 8.96 19.95 21.45 3.49 9.66 _

12.48

12.45

11.75

6.86

11.84

11.61

13.05

0.90 20.54 2.80 1.68 0.99 8.03 16.32 20.97 1.72 3.32 1.21 1.24 8.21 1.06 0.62 10.31

23.41 23.35 19.23 31.75 23.41 1.00

23.39 19.68 24.40 29.36 22.11 1.19

23.39 21.45 23.19 29.01 22.01 1.09

13.52 21.64 24.47 29.49 11.75 0.62

15.26 24.99 24.88 34.87 13.25 0.61

21.61 18.87 27.85 31.68 21.61 1.14

20.87 20.60 27.84 30.69 20.87 1.01

22.71 21.45 25.90 29.94 22.71 1.06

20.93 23.41 23.51 29.57 19.20 0.89

0.55

15.68 3.25

0.42 0.69

10.41 1.57

14.18 2.71 4.05

12.28 1.09

13.40 2.87 2.32

0.90 1.76

19.36 5.46 1.33

14.20 1.66 0.91

9.63 1.11 0.50

17.63 3.04 1.10

7.21 0.93 0.72

3.53 16.32 15.76 1.78 -

21.43 13.42 15.71 1.39 -

5.18 6.18 8.87 0.68

14.04 16.44 20.63 1.74

3.59 7.37 8.49 0.56

9.58 1.38 7.00 7.25 8.78 0.74

5.36 0.99 2.07 4.59 6.77 0.00

12.02 2.08 6.15 11.71 10.98 1.18

15.18 2.27 0.68 7.95 16.60 18.24 1.32

22.54 4.15 6.80 17.60 27.38 2.81

0.68

-

0.73 0.46 2.68 0.65

1.08 8.30 -

2.07 1.27 1.15 2.08

1.17 0.77 1.81 0.48

2.13 1.56 1.50 1.37

1.14 0.81 1.20 0.79

2.19 0.00

4.45 -

8.48 0.45

1.38 _

7.11 -

2.16 _

0.45 1.43 0.85 1.48 0.82 2.94 _

0.88 0.92 1.98 2.19 _

2.00 1.15 0.62 1.03 4.58 _

0.43 2.73 1.60 0.64 1.54 9.04 _

1.36 2.39 1.48 1.55 1.33 7.25 -

-

-

0.40 23.88 4.39 0.82 7.71 16.95 21.78 1.82 0.26 0.72 3.01 1.28 0.72 1.28 6.21 -

EFFECTS OF DIETARY PHOSPHATIDYLCHOLINE

AND CHOLESTEROL ON MARINE SHRIMP

175

TABLE 7 (Continued) Fatty acid

PC(%) CS(%) 22: ln9 22: 5n3 22:6n3 24:o 24:l Total n3 f.a. Total n6 f.a. Total n9 f.a. Total saturatedf.a. n3 PUFA* n3fn6

Diet 7

1

2

3

4

5

6

0 0

1.25 0

2.5 0

5 0

0 0.5

1.25 0.5

1.56 _ 2.03 _

1.08 2.33 I.10

0.53 4.25 0.55 7.94 15.20 -

0.24 0.28 6.14 _

8.75 3.58 -

2.5 0.5 4.81 7.80 -

8

9

10

11

12

5 0.5

0

1.25

2.5

I

1

I

5 1

7.58 2.83 -

6.48 0.39 0.61 6.29 10.78 0.12

4.21 9.64 18.36 17.27 15.87 6.31 11.47 5.01 12.04 6.97 15.76 19.07 10.13 23.56 10.10 10.44 7.69 13.17 9.97 22.85 17.69 12.70 21.85 18.20 14.87 14.04 22.27 24.05 27.56 36.98 30.99 33.87 21.94 33.92 19.71 34.43 4.21 7.87 16.97 16.59 14.13 5.75 10.7+ 5.01 10.87 0.60 0.61 0.96 1.70 0.67 0.62 1.10 0.65 0.91

21.75 21.38 21.99 25.14 20.43 1.02

3.36 -

0.95 0.89 4.42 0.45

13.43 30.19 24.14 30.70 10.61 0.44

13.33 24.34 25.30 33.13 II.52 0.55

*n3 PUFA=20:5n3+22:5n3+22:6n3. DISCUSSION

D’Abramo et al. ( 198 1) indicated that refined soy phosphatidylcholine is more effective in reducing H. americanus mortality than bovine phosphatidylethanolamine, soy phosphatidylinositol, non-phospholipids such as hydrolysis products of soy phosphatidylcholine, and fatty acids and taurocholic acid. Bonito-egg phosphatidylinositol was found to be more effective in promoting P. juponicus larval growth than any other type of phospholipid (Kanazawa et al., 1985). In the present study, purified phosphatidylcholine derived from soybean lecithin was used and the results suggested that I .25% was enough to promote significant shrimp growth. Commercial grade soybean lecithin is usually composed of approximately 30% phosphatidylethanolamine, 23% phosphatidylcholine, 18% phosphatidylinositol and other components. According to the suggestions of Kanazawa et al. ( 1985 ), the growthpromoting components are about 40% of soy lecithin (23% phosphatidylcholine + 18% phosphatidylinositol). Purified phosphatidylcholine, thus, should be more than twice as effective as soy lecithin in promoting shrimp growth. Significantly improved growth and food conversion were obtained when the cholesterol level was 0.5% or higher. The survival was much improved with the supplementation of 1% cholesterol. These values are well within the range of the requirement levels obtained in the other penaeid species. The cholesterol requirement of P. penicillutus, thus, is no exception to that of the other penaeids. The assumption that cholesterol and phospholipids may interact in improving growth and survival of crustaceans deserves more re-thinking. Re-

176

H.Y. CHEN AND J.S. JENN

lated studies so far have yielded more evidence against the assumption. Teshima et al. ( 1982) suggested that the effects of cholesterol in improving growth and survival of P. juponicus larvae are not affected by the dietary levels of soybean phospholipids. The final weight of juvenile H. americanus lobsters fed cholesterol and soy lecithin in combination failed to show significant interaction effect (Kean et al., 1985 ). The present research also showed insignificant interactions between dietary cholesterol and phospholipid on growth, food conversion and survival of the shrimp. It is, thus, very possible that the significance of the interaction between cholesterol and lecithin in promoting crustacean lipid utilization, growth and survival is not as important as has been suggested previously. Work with Penaeus japonicus (Kanazawa et al., 1977), Pandalus montagni (Clarke, 1979) and other crustaceans has described the preferential incorporation of dietary PUFA into body polar lipids. Gopakumar and Nair ( 1975 ) found 0.7 to 1.2% wet weight lipid in the tail muscle tissue of live species of wild Indian penaeid. Colvin ( 1976) reported 3.94% dry weight lipid in cultured P. indicus, and this rose to 6% when the shrimp were fed diets supplemented with various seed oil. Cultured P. merguiensis has a lipid content of 1.99% fresh weight (Clarke and Wickins, 1980). In the present study, the shrimp fed on the diets containing the same level of lipid showed significant difference in muscle lipid content. Dietary lipid composition plays an important role in influencing the muscle lipid level. The fatty acid composition of the polar fraction in the muscle tissue lipid was much influenced by the dietary inclusion of phospholipid. Phosphatidylcholine and soybean oil have a very similar fatty acid profile which is high in 18 : 2n6 (62.95% in phosphatidylcholine and 56.60% in soybean oil). When fed to shrimp, the fatty acids in the phosphatidylcholine were better retained in the polar lipid than those in the soybean oil. The polar lipid fraction accounted for about 80% of the muscle lipids. More than 60% of the polar lipids is phospholipid. Although the retention of phospholipids in the muscle cannot be related to the dietary supplement, the fatty acid prolile of dietary phospholipid is strongly reflected in the polar lipids in the muscle. These results indicate a dynamic metabolism in the muscle phospholipid pool in which the phospholipids are replaced by the phospholipids of the dietary origin. ACKNOWLEDGEMENTS

This investigation was partly supported by funds from the Council of Agriculture and the National Science Council (NSC76-020 1-B 11O-04) of the Republic of China to the senior author. We thank Dr. Wenli Jwuang of FuJen University, Taipei, for making purified phosphatidylcholine available to the study. Rosa Wu contributed her time and efforts in every phase of the research.

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