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Nutrient requirements and growth of the sea cucumber, Apostichopus japonicus

Sun Huiling, Liang Mengqing, Yan Jingping and Chen Bijuan

Yellow Sea Fisheries Research Institute, Qingdao, China

Abstract

Research into sea cucumber is a relatively recent field of interest for the aquaculture sector. There are only a limited number of reports on the feeding and growth of sea cucumber juveniles. The present paper summarizes the latest results on the nutritional requirements of Apostichopus japonicus. A first set of feeding experiments with juvenile sea cucumbers were conducted over 70 days using an artificial feed, mainly composed of fish meal, Sargassum thumbergii and lees (by-products from wine and beer production). Using chromium oxide as a marker, the authors determined that the weight gain rate and feed digestibility increased with the protein content of the diet. The optimal protein content was estimated at 21.5%. Based on a second growth experiment over a 40-day period, during which five different feed formulas were tested, the results indicated that the weight gain rate was maximal when the diet was rich in the following amino acids: threonine, valine, leucine, phenylalanine, lysine, histidine and arginine. Furthermore, the highest growth rates were obtained when the ratio between calcium and phosphorus (Ca/P) content ranged from about 6.8-8.8:1. On the other hand, the weight gain rate decreased when the sea cucumber juveniles were given a fibre rich diet.

Keywords: Nutrition, protein, amino acid, feed formula

Introduction

There are about 1 100 species of sea cucumbers in the world. Over 100 species are present in China of which more than 20 species are edible and of commercial value. These include Apostichopus japonicus, Actinopyga mauritiana, A. lecanora, Holothuria nobilis, H. scabra, Bohadschia marmorata, Stichopus chloronotus and Thelenota ananas.

The most valuable local species, Apostichopus japonicus (Echinodermata, Holothuroidea, Aspidochirotida, Stichopodidae), is widely distributed in the waters off China, Japan, Korea and Russia. In China, the species is mainly distributed in the Bohai Sea and the Yellow Sea. Studies on A. japonicus started in the 1950s when scientists from China and Japan first tried to develop breeding techniques. During the 1980s, Chinese scientists made a break through in the larval rearing of the sea cucumber and made considerable progress in the culture techniques on a commercial scale. Over the last decade, the farming industry of A. japonicus has been developing rapidly. As of 2003 in the Shandong Province, a total volume of 145 000 m3 of larval rearing facilities is being used to produce up to 1.27 billion juveniles. It is estimated that the cultivation areas cover some 15 000 hectares and that a harvest of 2 250 tonnes can be expected.

In recent years, studies on A. japonicus have been focused on culture techniques in order to improve and expand the culture scale. Numerous diets were tested to optimise sea cucumber culture. However, there are very few reports available on the basic nutritional requirements for the optimal growth of this species. Most commercial feeds lack the essential ingredients to meet the nutritional requirement of this holothurian. The present paper summarizes the latest results on the nutrition and growth of A. japonicus. It is expected that these data can provide a scientific basis for the development of an improved commercial feed.

Materials and methods

Experiment No. 1 - Effect of protein content on the digestibility of food and weight gain of sea cucumbers

The influence of different proteins on the digestibility of the feed and growth rate of A. japonicus was tested. The experiment, over a period of 70 days, was conducted in an indoor concrete tank (4x6 m) in which 12 rectangular net-cages (90x80x100 cm) were placed for different experimental treatments.. Artificially bred juveniles of A. japonicus, obtained from the Penglai hatchery in Shandong Province, were used. The sea cucumber juveniles were randomly distributed in the twelve cages. The initial weight of selected individuals ranged between 4.5-4.8 g. They were distributed in groups of 30 individuals per cage. Four treatments were scheduled for the experiment. Each treatment had three replicates. During the experimental period the sea cucumbers were fed with four different diets once a day. The amount of feed administered equalled 3 % of the body weight. The tanks were aerated and the water temperature maintained between approximately 15 to 20 °C. The experimental feed formulas tested are listed in Table 1.

Table 1. Diet composition and protein content.

Components

Composition of diet (%)

Diet 1

Diet 2

Diet 3

Diet 4

Sargassum thumbergii

45

39

30

23

Fish meal

0

6

15

22

Lees

20

20

20

20

Mud

15.5

15.5

15.5

15.5

Kelp powder

7

7

7

7

Yeast

3

3

3

3

Vitamin

0.5

0.5

0.5

0.5

Mineral

0.5

0.5

0.5

0.5

Soybean meal

5

5

5

5

Bran

3

3

3

3

Chromium oxide (Cr2O3)

0.5

0.5

0.5

0.5

Protein content

14.7

17.7

19.1

21.5

The sea cucumber juveniles were acclimated to the four experimental diets for a month. After a month, faeces samples were collected by siphoning the particles from the tank bottom. The faeces collected were then centrifuged, dried in an oven at 65 °C for analysis. Both freeze-dried food and faeces were finely ground prior any analysis took place.

Crude protein content was determined by the Kjeldahl method. Crude fibre was determined by an automatic analyser (Fibertec, Tecator-Sweden). Amino acids were analysed using an automatic apparatus (Hitachi Model 835-50, Japan) with an ion exchange column. Chromic oxide was determined by a wet-acid digestion method (Furukawa and Tsukahara, 1966). The digestibility and weight gain rates were calculated as follows:

Weight gain rate = (Winitial weight - Wfinal weight)/ Winitial weight

Apparent digestibility rate = (1-dietary Cr2O/fecal Cr2O3 x faecal nutrient/dietary) x 100

Experiment No. 2 - Relationship between amino acid composition, Ca/P ratio and fibre content on the growth rate of sea cucumbers

The juvenile sea cucumbers used were artificially raised and were cultured in indoor concrete tanks. Seawater was maintained between 8-12 °C and was constantly aerated. Seawater in each culture tank was completely replaced daily during the 40-day experimental period. Each treatment had two replicates, in which 50 sea cucumber with an initial weight of 2.1 g were used. Table 2 shows the composition of amino acid in each experimental diet.

Table 2. Composition of amino acid in five experimental diets.

Amino acid

Composition (% - 100 g of the formulated feed)

Diet 1

Diet 2

Diet 3

Diet 4

Diet 5

Asp

1.40

1.34

1.22

1.68

1.45

Thr

0.63

0.62

0.55

0.55

0.62

Ser

0.59

0.61

0.54

0.54

0.61

Glu

2.88

3.06

2.32

2.24

3.23

Gly

0.78

0.75

0.7

0.69

0.77

Ala

0.89

1.02

0.8

0.74

1.02

Val

0.91

0.94

0.85

0.76

1.00

Met

0.14

0.10

0.13

0.31

0.13

Ile

0.63

0.65

0.59

0.56

0.67

Leu

1.11

1.38

1.04

0.92

1.35

Tyr

0.19

0.21

0.00

0.00

0.15

Phe

0.63

0.72

0.54

0.60

0.66

Lys

0.92

0.77

0.79

0.73

0.83

His

0.18

0.20

0.18

0.15

0.19

Arg

0.75

0.69

0.63

0.71

0.71

Protein content (%)

16.64

17.74

14.77

15.38

17.14

Results and discussion

Experiment No. 1 - Effect of protein content

The weight gain rates of cultured sea cucumbers fed on different formulated feeds are shown in Table 3. Statistical analysis indicates that there is significant difference between the different treatments tested. The experiments suggest that the growth rate and digestion efficiency of cultured animals increase with the protein content. The highest growth rate occurred when food had a protein content of 21.5 %, which is consistent with the protein content in the meat of fresh sea cucumber. However, it remains to be tested whether further increases in protein content in the food will further increase the growth rate of cultured sea cucumbers.

Table 3. Effect of protein content on food digestibility and growth of sea cucumber juveniles.

Parameters

Diet

1

2

3

4

Protein content (%)

14.7

17.7

19.1

21.5

Digestibility rate (%)

40.6a

48.2b

55.8c

63.9d

Weight gain rate (%)

105.8a

113.8b

122.7c

145.6d

Survival rate (%)

93.3

98.3

90.0

93.3

Statistical significance was determined using analysis of variance and Duncan’s new multiple range test. Values (mean of three replicate groups) in each column with a different letter are significantly different (P<0.01).

Experiment No. 2 - Relationship between amino acid composition and growth of sea cucumber juveniles

As shown in Table 4, the highest weight gain rates was observed with diet 1 and diet 5, in which there were high contents of both lysine and arginine which are also essential amino acids for fish and shrimp. Other diets yielded a slightly lower weight gain rates. The results obtained seem to reveal that lower content of lysine or absence of lysine can influence the growth rate of sea cucumbers.

Table 4. The growth of sea cucumber during experimental period.


Experimental diet

1

2

3

4

5

Weight gain rate (%)

174.1

119.2

149.3

157.6

159.2

Survival rate (%)

100.0

99.6

98.5

100.0

98.0

Experiment No. 2 - Relationship between Ca/P ratio in the diet and growth rate of sea cucumber juveniles

The Ca/P ratio is a crucial factor influencing the growth rate of juvenile sea cucumbers. The results of Table 5 show that the highest weight gain rate was observed with Ca/P ratio ranging from 6.78 to 8.80. Sea cucumber fed with diet 1 and diet 5 grew faster than those supplied with diet 2, diet 3. Although the ratio of Ca/P in diet 4 is as high as 9.41, its growth gain rate is almost the same as that for diet 5. The Ca/P ratio in all diets is higher than that measured in the sea cucumber body (5.36). This value is also far higher than what is found in fish (Ca/P ratio values of common carp and red sea bream, Pagrosomus major, are 0.5 and 0.13, respectively, and that of juvenile shrimp is 0.59). From the results it appears that the optimal Ca/P ratio in a sea cucumber diet may be between 7 and <9. It is apparent that the growth gain rate of sea cucumbers is influenced by numerous factors and therefore a careful diet formulation is required to ensure optimal growth.

Table 5. The effect of Ca/P ratio on weight gain rate of sea cucumber juveniles.


Experimental diet

1

2

3

4

5

Ca/P ratio

8.80

5.81

6.84

9.41

6.78

Weight gain rate (%)

174.1

119.2

149.3

157.6

159.2

Experiment No. 2 - Relationship between crude fibre content and growth of sea cucumber juveniles

The experimental results seem to indicate that the weight gain rates decreased with increasing dietary fibre contents (Table 6). So far no enzymes for digesting fibre have been identified and isolated from the digestive system of sea cucumber. The authors therefore conclude that crude fibre is not a necessary source of energy.

Table 6. The effects of fibre on the growth rate of sea cucumber juveniles during the experimental period.


Experimental diet

1

2

3

4

5

Crude fibre content (%)

4.3

11.2

16.5

8.6

8.1

Weight gain rate (%)

174.1

119.2

149.3

157.6

159.2

Acknowledgements

The authors would like to thank Professor Chen Jiaxin, who works at Yellow Sea Fisheries Research Institute of the China Academy of Fisheries Sciences, for his all help in this meeting. Sincere thanks also go to Dr Annie Mercier and Dr Jean-François Hamel for helping the authors with the abstract and final version of the paper.

References

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