Previous Page Table of Contents Next Page


Session III. Aquaculture advances


Pond culture of sea cucumbers, Apostichopus japonicus, in Dalian

Chang Yaqing1, Yu Changqing2 and Songxin2

1 Dalian Fisheries University, Dalian, P. R. China;2 Liaoning Province Fisheries Seeds Management Bureau, Dalian, China

Abstract

There are more than 7 000 hectares of ponds used for the culture of Apostichopus japonicus and 2 000 hectares of ponds used for polyculture of A. japonicus and shrimp in the Dalian area. The best results are obtained in leak-proof ponds with a muddy sand bottom. The size of a pond is usually between 2-6 hectares and the water depth maintained at 1.5-2.5 m. The seawater is changed by opening and closing the sluice gates with the change of tide. The salinity is 25-35 and the water must be clean and unpolluted. The survival rate increases with the release size of the juveniles: individuals larger than 2 cm will have a survival rate of at least 20-30 %. The stocking density of sea cucumbers and shrimp is 100-150 000 and 15-30 000 per hectare, respectively.

During the culture, the quality of the seawater and the growth of sea cucumbers and shrimp should be monitored daily and the food supply adjusted accordingly. Unwanted algae and harmful organisms should be removed from the ponds on a regular basis. The depth of the water must be maintained throughout summer and winter. After about 1.0-1.5 years, the sea cucumbers can either be harvested by divers or collected after the ponds have been adequately drained.

Keywords: China, co-culture, prawn, grow-out

Introduction

The sea cucumber, Apostichopus japonicus Liao, can be found along the Korean Peninsula, Japan, the eastern shores of Russia and the northern coast of China PR. It is a favourite seafood in these areas, especially in China PR. Research on its aquaculture began in the middle of the 1980s. There was great progress made in the breeding and larval rearing of A. japonicus, which promoted the rapid development of the aquaculture industry in Dalian, Yantai, Weihuai and Qingdao. In the early 1990s, many coastal ponds traditionally used for shrimp farming were abandoned due to the emergence of diseases. Many of these ponds were restored and used for sea cucumber aquaculture also in polyculture with different marine shrimp species. Both methods proved to be financially profitable.

Pond culture of A. japonicus is restricted to the Liaoning and Shandong Provinces and is mainly centred in the Dalian area. Over 7 000 hectares of ponds are used for sea cucumber culture. In addition, approximately 2 000 hectares are in use for farming the holothurian in polyculture with shrimp.

Methods

Optimal culture pond conditions

Pond size and water quality - Ponds are usually located in the intertidal zone for convenience of water exchange. The salinity should be maintained above 28 all year round, however, it can drop to 24-26 over a short period in summer. Water quality should remain high and it can be renewed by opening and closing the sluice gates. The optimal pond size is usually between 2-6 hectares with a water depth maintained at 1.5-2.5 m.

Pond cleaning and sterilization - The best farming results are obtained in leak-proof ponds with a muddy sand substratum which requires sterilization prior to the rearing phase. This is done by first removing the bottom silt. At this point the pond is filled with seawater and the level adjusted to 0.2-0.3 m. Calcium oxide or bleaching powder is subsequently added. The use of the two sterilizing substances is described in Table 1.

Table 1. Pond sterilization methods.

Chemical

Method

Dosage

Action

Efficiency

Calcium oxide

Dissolve and distribute
in the pond

750 kg/ha.
Water depth: 0.05-0.1 m

1. Kills fish, crab, algae,
parasites and bacteria
2. Increases pH

7-15 days

Bleaching powder

Dissolve and distribute
in the pond

75-150 kg/ha.
Water depth: 0.05-0.1 m

As above

4-5 days

Settlement substratum - According to the natural behaviour of the sea cucumber, the pond bottom requires a layer of an adequate substratum for larval settlement to occur. Stones, roof tiles, bricks and other suitable structures can be used. The quantity of the substrate should be in the range of 150-1 500 m3/ha, however this can vary depending on the pond characteristics and production method employed. Stones remain the best choice, each of about 15-40 kg in weight. The settlement substratum should be added to the pond one month prior to the introduction of the sea cucumber juveniles.

Water conditioning - In order to ensure the right quantity of diatoms, the water should be inoculated at least 15 days before the juveniles are seeded. The most common fertilizer used is urea at about 30-60 kg/ha.

Juvenile rearing and growout

Time - The growout season can commence either in September/October or in March/April when the seawater temperature ranges between 10-15 °C. In a polyculture situation the shrimp postlarvae are usually introduced in May-June.

Transportation of juveniles - The juveniles are placed in temperature controlled boxes for transportation. They should not be fed for 1-2 days prior to this operation. The temperature should be maintained below 18 °C. The shrimp postlarvae are generally transported in oxygen filled plastic bags with a sufficient quantity of seawater.

Juvenile size and rearing density - The juveniles may be from the wild or hatchery produced. Juveniles usually range between 2-10 cm in length and their stocking density varies depending on the pond conditions, food supply and availability of settlement surfaces. The amount of sea cucumber juvenile released is 15-40 individuals/m2 for individuals measuring 2-5 cm, 15-25 individuals/m2 for individuals of 5-10 cm, and 5-8 individuals/m2 when they are 10-15 cm in length.

There are two methods for releasing the juveniles. The first one is to place them in the sea bottom directly by hand or simply releasing them from a boat using individuals larger than 4-5 cm. The second method, used when handling individuals smaller than 3 cm, is to place the juveniles in mesh bags with an opening at one end. The mesh bags are 30x25 cm in size and each one may contain up to 500 individuals. They are placed beside the settlement substratum.

The shrimp species used for polyculture with sea cucumber are the Chinese or Japanese shrimp. The shrimp postlarvae are usually 2-3 cm in length and are seeded at a density of 3-6 individuals/m2.

Feeding - Sea cucumber juveniles usually do not require any additional food supply. However, the addition of food is necessary to maintain a high rearing density and to favour growth during spring and autumn. Grounded pieces of Sargassum and Zostera are generally used.

Pond management - The seawater is renewed by opening and closing the sluice gates with the change of tide. About 10-60 % of the total seawater should be exchanged depending on the water quality and temperature in the ponds. In summer, the water level in ponds should be kept higher in order to maintain a lower temperature. The salinity is maintained by regular water changes. The temperature, salinity, pH and oxygen levels should be monitored daily as well as the growth, survival rate and behaviour of the sea cucumbers.

During the winter months, the following additional tasks need to be performed:

1. Maintain the water level at 2 m.

2. Removal of ice formations from the surface of the pond to keep the air-water interface free and ensure acceptable oxygen concentrations in the pond.

Harvest - The sea cucumbers are collected when they reach 150-200 g. Harvesting is done following the drainage of the ponds or with the use of SCUBA diving equipment. The shrimp are generally collected using nets placed at the sluice gates.

Production

The production levels of sea cucumber in pond culture vary between 1 500-10 000 kg/ha depending on the culture conditions, the quantity of juveniles released, their initial size and initial pond preparation (Table 2).

Growth and survival rates

The time needed to grow the sea cucumbers to a commercial size varies between 10-18 months, whereas the shrimp attain the desired size in about 4-6 months. The survival rate of sea cucumbers may vary between 10-90 %.

Table 2. Sea cucumber production along the coast of Dalian using different pond sizes, juvenile sizes and stocking densities.

Trial
No

Area (ha)

Beginning of culture (year/ month)

Size of released juveniles (cm)

Number of juveniles per pond

Total duration of culture (months)

Total harvest (kg)

Weight per individual (g)

1

0.35

1994/11

2.5

170 000

17

3 500

120-140

2

0.33

1997/05

6.5

120 000

10

3 100

100-120

3

2.00

1999/04

8.6

103 000

12

8 260

130-210

4

2.00

2000/04

7.3

156 000

13

8 870

120-195

Table 3. Relationship between survival rate and size of juvenile sea cucumbers released at the start of the grow out phase.

Sea cucumber length
(cm)

Survival rate
(%)

2-5

10-35

5-10

30-80

10-15

60-90

Financial aspect of pond culture

The net income generated by sea cucumber pond culture may fluctuate between 7 500 and 5 0 000 US$/ha. It is currently one of the most attractive aquaculture businesses in northern China. Numerous local farmers and entrepreneurs have become wealthy thanks to this industry. The sector is rapidly expanding.

The importance of water temperature

The growth rate of sea cucumbers is closely related to the water temperature maintained in the pond. The best growth rates are observed in spring and autumn. The body weight of an adult sea cucumber will decrease by roughly half when the water temperature is above 22-24 °C in summer. The growth rate and generally all biological activity are very low during winter months when the temperature is below 2 °C.

Conclusion

Ponds can be used for culturing sea cucumbers alone or in polyculture with different species of shrimp. The best production results are obtained in leak-proof ponds with muddy sand bottoms. Seawater is exchanged by opening and closing the sluice gates during tidal movements. The optimal cultured density of sea cucumbers is 100-150 000 per hectare. The seawater depth in the ponds must be maintained at its optimal level throughout summer and winter. After approximately 1.0-1.5 years the sea cucumbers are ready for harvesting. The industry currently yields a very good return on the initial investment.


Previous Page Top of Page Next Page