FI:DP/CPR/85/080/ Field Document 12 December 1987

A report prepared for the project
Demonstration of prawn culture in Xincun

based on the work of

J. Honculada-Primavera
Consultant

This report was prepared during the course of the project identified on the title page. The conclusions and recommendations given in the report are those considered appropriate at the time of its preparation. They may be modified in the light of further knowledge gained at subsequent stages of the project.

The designations employed and the presentation of the material in this document do not imply the expression of any opinion whatsoever on the part of the United Nations or the Food and Agriculture Organization of the United Nations concerning the legal or constitutional status of any country, territor or sea area, or concerning the delimitation of frontiers.

SUMMARY

An evaluation was made of available hatchery facilities and existing procedures in order to plan out a strategy for captive broodstock and maturation for the prawn Penaeus orientalis in Xincun, China. Information on the life history of the species was valuable in outlining specific activities in three general areas of the breeding process -- Spawning, induced maturation, and overwintering of broodstock. Facilities and equipment required to support the breeding effort are identified including a maturation building and tanks for-maturation and spawning. Finally, training was given to the project staff in the form of lecture-slide presentations and discussions in preparation for the April-May 1988 breeding work.

ACKNOWLEDGEMENTS

The Consultant would like to acknowledge the assistance extended by officials of the China International Centre for Economic and Technical Exchanges, Huang Hua County and Xincun Township. Particular mention is made of Mr. Ren Guo Zheng for logistical support in Xincun, Ms. Yan Yu Kun for English interpretation and facilitating arrangements, and Ms. Liu Heng for valuable technical interpretation.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 1987

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TABLE OF CONTENTS

1. INTRODUCTION

1.1 Terms of Reference

1.2 Background Information

2. ACTIVITIES

3. LIFE HISTORY OF P. ORIENTALIS

4. CULTURE

4.1 Hatchery

4.2 Grow-out

5. RECOMMENDATIONS

6. PLAN OF ACTIVITIES (1987–88)

Appendix 1: Itinerary

Appendix 2: Persons Met

Appendix 3: Outline of Lectures Delivered

Appendix 4: References

Appendix 5: Equipment needed for Maturation/Spawning Work

LIST OF FIGURES

1. Floor plan of maturation building

2. Side view of maturation building showing details of maturation tank, drain canal and lighting

3. Maturation tank

1. INTRODUCTION

1.1 TERMS OF REFERENCE

The Government of the People's Republic of China, assisted by the United Nations Development Programme and the Food and Agriculture Organization of the United Nations, is engaged in project CPR/85/080, Demonstration of prawn culture in Xincun.

As part of the project operations, FAO appointed Ms J. Honculada-Primavera as consultant (induced maturation and spawning) for a total of two months with the following terms of reference:

In close collaboration with the National Project Director, project staff and the Qingdao Institute:

• to help shorten the prawn breeding period through a combination of hermonal, nutritional and environmental manipulation;

• to demonstrate improved techniques of prawn breeding including hermonal techniques of induced maturation of female prawns;

• to prepare a mission report.

Note: There may be no need at present to shorten or advance the breeding period from April-May to earlier in the year. This is because pond grow-out is limited to the May-October period when water temperature is warm; therefore demand for fry will also be limited to late April up to early June.

1.2 BACKGROUND INFORMATION

China is one of the world's leading producers of prawns with up to 60% now contributed by farming which was introduced in 1964. Xincun is a small coastal village in Hebei Province, northern China, where prawn culture covers around 3 800 mou (250 ha) since it started in 1983.

The present project (CPR/85/080) has established a prawn hatchery to provide fry or seedlings to farmers in Xincun and neighbouring townships. For the long term, the project aims to replace wild spawners with broodstock matured in captivity.

2. ACTIVITIES

During the initial meeting with CICETE, Ministry of Foreign Economic Relations and Trade, and Xincun Township officials, it was recommended that the 2 man-months consultancy be split in order to enable the consultant to return during the early 1988 breeding season. The off-season visit when no prawn broodstock are available (September 1987) could be spent on familiarization with the project, recommendations for preparatory work, and training of local technicians. Actual induced breeding work could be done in April-May 1988, the natural breeding season of the Chinese prawn.

A 2-week trip was made to the project site in Xincun Township, Huang Hua Country, Cangzhou Prefecture in Hebei Province, northern China, five hours by car from Beijing. Observations and discussions were made with prawn hatchery technicians and farmers and with local township officials and staff of the Institute of Oceanology in Qingdao.

During the stay in Xincun, the consultant also gave lecture-slide presentations followed by discussions to hatchery technicians from Xincun and neighbouring villages on the following topics:

1. 1. Biology of Penaeid Prawns
2. 2. Prawn Broodstock and Induced Maturation

Appendix 1.2 and 3 give the Consultant's itinerary, list of persons met and outline lectures delivered.

In order to plan out a captive broodstock strategy and specific activities for the 1988 breeding season for the Xincun hatchery, background information on the life history of the species was considered valuable. The following sections give a brief description of the life cycle and culture practices (in Xincun) of the Chinese prawn as obtained from available literature and from the Institute of Marine Scientific and Technological Information in Tientsin (Appendix 4) and from discussions with hatchery technicians, prawn farmers and Institute of Oceanology staff.

3. LIFE HISTORY OF P. ORIENTALIS

The Chinese prawn Penaeus orientalis (*) has two populations: a larger Chinese population with bigger sizes and a smaller Korean population. Its distribution is from 33o to 40oW latitude and from 118o to 125oE longitude.

The overwintering population in the Yellow Sea starts to migrate northward in late March arriving a month later in the spawning grounds in the estuaries along Bohai Sea and the southern coast of the Yellow Sea. Females arrive ahead of the males perhaps to gain first access to the feeding grounds as nutrition is important for ovarian maturation and subsequent spawning. (Fishermen say that arrival of the males in a given place indicates that no more females are forthcoming.)

The earliest and latest spawning dates are 2 May and 18 May. respectively, when the sea bottom has temperatures of 15 to 18°C and salinities of 23 to 30 ppt. Females have 500 000 to one million eggs and most of them die after spawning at one year of age. Typical of other penaeid species, the postlarvae migrate towards the coastline with some moving more than 50 km upriver. From June onwards, these coastal shallows of 6–10 m depth act as nursery grounds for the postlarvae. By late August when the juvenile prawns reach 60–100 mm body length, they start to move to deeper waters for food. In September when they are 150 mm long, they move in groups or schools to waters over 20 m deep. (Schooling behaviour is also exhibited by P. indicus and P. merguiensis, other species of the subgenus Penaeus to which P. orientalis belongs.)

Although it is possible that the prawns mate at a younger age and smaller size as with other penaeid species, most scientific papers (in English) report that first mating of P. orientalis occurs in October when females are 170–180 mm (60–65 g) and males 150 mm (45 g) after which the majority of males die. Assuming the females do not molt (and therefore keep the spawn masses in their thelyca) until they spawn the following May, there is no biological need for the males.

(*) Penaeus chinensis is the accurate but less popular name

By mid-November when the bottom waters of Bohai Sea drop to 12–13°C, the prawns start moving southward in schools and reach the Yellow Sea wintering grounds up to 1 000 km away in late January. There they disperse and embark on the reverse migration to the spawning grounds in the second half of March as temperatures start to warm up. As stated earlier, most females die after they spawn in May but tagging experiments show that a few prawns enter the spawning grounds a second time meaning they survive up to two years of age.

There are three distinct fishing seasons based on the life cycle -- in spring (spawning population) and autumn (feeding-growing phase) in the Bohai Sea and in winter-spring (wintering-migrating phase) in the Yellow Sea. Most catches are in the autumn, from fixed nets using small boats and from trawls using larger vessels.

Catches have fluctuated between 10 000 and 90 000 m depending on variation in recruitment, with some indication that the latter is related to the abundance of the spawning population. It has been suggested that the present government ban on spring fishing north of Chengshantou, Shandong Province be extended to 35oN as the prawns start their spawning migration in March.

4. CULTURE

As with other hatcheries in China, the Xincun hatchery operates only during April-May so that harvested postlarvae can be stocked and reared during the May-October season with warm water temperature favourable for growth in the ponds.

4.1 HATCHERY

Built in early 1987, hatchery facilities consist of 16 36 m3 larval tanks of 6 × 4 × 1.7 m and 2 60 m3 larval tanks of 10×4×1.7 m (total capacity 700 m3), 8 one m3 Artemia tanks, outdoor sedimentation pond of 200 m3, a seawater pump (cap. 60 m3/h, a 300 m3 seawater storage tank, a 4 m3 boiler, and 2 air blowers (cap 7–10 m3/min. each). Instruments and equipment ordered through UNDP are shown in Appendix 4.

Gravid females caught from the Bohai Sea are stocked up to 200 at a time in the 36 m3 tanks. There are no broodstock or females matured in captivity. The females are removed after spawning and the eggs are hatched directly in the larval tank.

Initial larval stocking density is up to 600 nauplii/litre. The larval tanks are provided with airstones, and temperature is maintained at around 20°C (by steam from boiler running through iron pipes); salinity is 20–30 ppt. Daily water change ranges from 10–30% up to 70% of total volume, depending on larval density and other factors. Feeding consists of diatoms at the zoea stage, the rotifer Brachionus plicatilis at mysis and brine shrimp (Artemia) at postlarva (PL)1. The fry are harvested at PL5 for direct stocking into grow-out ponds in May and June.

In 1987, approximately 150 million prawn try were produced by the Hatchery.

4.2 GROW-OUT

The farm near the project site covers a total area of 24 ha and consist's of 2 ha-ponds each assigned to one person. Two weeks before stocking, the ponds are prepared by cleaning, flushing the bottom with water to reduce accumulated salt and application of organic fertilizer (from Japan) at 50 kg/ha. Hatchery fry at PL5 stage are stocked directly into the prepared ponds at 300 000–600 000/ha in May and June. A few hundred pieces of a non-predatory fish species with active jumping movements are introduced to increase oxygen in the water.

Prawn feeds using fish meal, corn powder, soybean cake, algal binder (Laminaria) and other raw materials are manufactured locally. The 4–5 prawn feed mills capacity 5 t/day) in Xincun also supply feeds to neighbouring villages. Feeding is done 4 times daily (06.00 h, 13.00 h, 18.00h and 12 midnight) following given feeding rates.

During the 25 September visit, at about 17.00 h, the prawns in one pond started jumping out of the water for about 4 min. It could have been a sign of stress as the prawns later suffered some mortalities. Probable causes were oxygen stress (prawn biomass of around 2 tons/ha, excess feeds and faecal wastes causing biological oxygen demand) and hydrogen sulphide build-up on the pond bottom. Recommendations to improve grow-out practices are given in a later section.

A 2 ha-pond harvested on 3 October 1987 produced about 3 000 kg or 1.5 ton/ha after 4 months and 10 days. Sizes ranged from 8 to 16 cm body length (8 to 30 g) with females in the larger size range. A random sampling of 100 prawns gave an exact 60 females: 40 males sex ratio.

Harvest involves completely draining a pond over a period of 6 h during the low tide. The prawns are caught in a 8–10 m × 1 m diameter bagnet attached to the canal side of the drain (sluice) gate. Twenty persons are needed to harvest one pond. Weighing of prawns, and placing in plastic trays into a truck with ice (for transport to processing plant) are done right in the pond near the drain gate.

5. RECOMMENDATIONS

1. The major objective of the project is to replace all wild spawners with captive broodstock by 1990, in consenance with government efforts to improve recruitment in wild prawn stocks by protecting the spawning population. Assuming the projected maximum of required broodstock of 10,000 per annual breeding-hatchery cycle, there is no alternative but to set up a separate maturation unit. At present the Xincun hatchery has no saturation phase, depending wholly on spawners caught from the sea.

2. Similarly, the spawning procedure has very little intervention with the females releasing eggs directly into the larval tanks. Many improvements are needed to separate potential disease carriers (unhatched eggs, shells of hatched eggs, weak nauplii and debris) from the healthy nauplii and to provide the optimum parameters for spawning as well.

3. As emphasized during the lectures and discussions, the nutritional and environmental requirements are different for each stage of the life history -- maturation, spawning, larval and postlarval rearing, and grow-out. The 36-m3 larval tanks may be unsuitable for purposes of maturation and spawning.

4. A maturation building with facilities for maturation, spawning, laboratory work (microscopes, dissection) and feed preparation (Fig. 1) is recommended for the long-term, if not the April 1988 activities. Details of maturation tank construction, air and water connections are shown in Figs. 2 and 3.

5. In addition to equipment already ordered through UNDP/FAO, some more instruments are needed specifically for maturation and spawning. (Appendix 4).

6. If resources allow the construction of a maturation building and related facilities, the full activities in the 1988 workplan (see following section) can be undertaken. If resources are limited, a compromise would be to construct the building itself with only a few units of maturation tanks and the laboratory, spawning and work areas. Correspondingly, all the spawning and some maturation activities can be conducted. If no new facilities are ready by April 1988, the existing larval tanks may be improvised for a few maturation exercises; most of the spawning activities can be undertaken.

7. The projected number of nauplii or larvae that can be produced by 40 units of 12 m3 maturation tanks (Fig. 1) will depend on the following:

   1. fecundity or number of eggs/spawning for ablated females (500 000 – 1 million for wild unablated females)

   2. hatch rates of eggs

   3. number of females stocked/tank

      1. 25–50 females/tank (1♀. 1♂ ratio)
      2. 50–100 females/tank (1♀: 0♂ ratio)

   4. maturation rate of ablated females

      The number of prawn fry or seeds that can be produced will depend mainly on the survival rate in the hatchery.

8. As mentioned earlier, information on the reproductive biology of P. orientalis is useful for planning future activities. A short trip to Qingdao for discussions with senior researchers in the Institute of Oceanology and Yellow Sea Fisheries Research Institute is therefore recommended for the April 1988 consultancy (before Xincun or midway through the work in Xincun).

6. PLAN OF ACTIVITIES (1987–88)

The planned activities for and leading to, the April-May 1988 breeding season fall under three general areas -- spawning, maturation and overwintering of pond broodstock. Some recommendations on pond culture are also included.

1. Spawning

Ideal tank size (diameter and depth) should be determined for P. orientalis. For this purpose, different sizes of commercially available plastic buckets (for household use) can be tried. Optimum spawning temperature should be established by testing 13°C, 16°C and 19°C to be maintained at ±1°C (using portable immersion heaters). Spawning tank water should be treated with 10 ppm chlorine and EDTA (ethylenedinitrotetraacetic acid). Gentle aeration should suspend the eggs in water but not disturb the females. Egg density should not exceed 3 000 eggs/litre.

For each experiment, nature of spawning (complete, partial or none), number of eggs, number of nauplii and hatch rate will be recorded to determine the best treatment. For successful complete spawnings, correlation between body size and fecundity will be established. New techniques in egg quality or classification (to predict hatch rates), egg washing and counting will be demonstrated.

2. Induced Maturation

The 12 m3 maturation tank prototype (Figs. 2 and 3) has been adopted in many hatcheries throughout the world because it provides the requirements for prawn maturation and is easy to manage as well. Aside from concrete, other materials such as wood, canvas or bricks may be used for construction.

Maturation will be induced in P. orientalis using unilateral eyestalk ablation technique proven successful for over 20 penaeid spicies in combination with optimum nutritional and environmental parameters to be determined or confirmed for this species. Ablation will be performed by means of cautery (burning the eyestalk with hot forceps) to minimize loss of blood.

Optimum temperature will be determined by testing 14°C 16°C and 19°C to be maintained by late heaters inside the 12 m3 tanks. Salinity will depend on incoming water (25–30 ppt) which will be recirculated (to conserve heat) rather than on flowthrough in the tank, pH will be maintained at 7.5–8.5. Light will be kept at a low intensity (around 100 lux) with a photoperiod of 14 h light: 10 h dark using blue, green or cool white fluorescent lights.

Broodstock or immature adults obtained from either the wild (sea) or overwintered ponds will be stocked at 4–8 pcs/m2 (300 g/m2) in the tanks. Sex ratio will depend on whether females do not molt and keep their sperm packets (therefore all-female population) or do molt and lose their sperm (therefore 1–2 females: 1 male) at the temperature level in the tanks established to be optimum for maturation.

Minimum and maximum sizes for maturation will be determined for females (test sizes 31–50, 51–70, 71–90 g) and males (test sizes 21–30, 31–40, 41–50 g). Ablated females will be checked for maturation and spawning of eggs with high hatch rates. Testes and spermatophores of males will be dissected and microscopically examined for normal mature sperm (with spikes).

Food will consist of fresh/frozen squid or shellfish 5–6 times and live marine worms (annelids) 1–2 times per week. Feeding will be done 2 times daily using feeding trays.

C. Overwintering of Pond Broodstock

It is envisioned that ultimately pond broodstock will be the major source of spawners for the hatchery. It is recommended that 1 000 prawns from the October 1987 harvest be stocked in the 400 m3 overwintering pond (50 × 15 × 0.5 m) near the warm water well. (The 1986–87 overwintered stock of 2 000 prawns suffered 60% mortality after 7 months probably due to high stocking density, among other factors). Temperature should be maintained at 15 to 25°C and feeding (trash fish, shellfish) carefully controlled to avoid fouling of pond bottom.

D. Pond Culture

1. Decrease stocking density from 600 000/ha to 200 000–300 000/ha, in order

   1. to increase survival rate from present 15–20%

   2. to increase harvest size from present 20 g body weight

2. Before stocking, introduce a nursery period of 30 days to produce PL35

   1. in nursery tank (inside hatchery) or in nursery pond

   2. to reduce mortality rate in ponds

3. Improve prawn pellet feed

   1. increase water stability from 30 min to 6 h by drying and improving binder

   2. better quality of raw materials, e.g., fish meal

4. Place 10% of feed in 4–6 feeding trays per pond

   1. check at each feeding for excess or lack of food

   2. check health or poor condition of prawns

5. Reduce amount of hydrogen sulphide (H2S) caused by excess feeds, faeces in ground bottom by

   1. tilling, exposing and drying soil

   2. spread fine sand over areas with H2S

6. In case of stress and mortality among prawns

   1. immediate water exchange, especially bottom layer of pond water

   2. install aerator if stock is 2 tons/ha or more.

Fig. 1 Floor Plan of Maturation Building

A - Maturation Tank (4 m ø × 1.2 m)

B - Drain Canal (0.5 m × 0.5 m)

C - Work and Feed Preparation Area (for portable one-ton tanks)

D - Laboratory Room (for microscope work)

E - Hallway (leads to spawning room)

F - Spawning Room (for spawning tanks)

Fig. 2 Side view of maturation building showing details of maturation tank, drain canal and lighting

Fig. 3 Maturation tank, 4 m ø × 1.25 m depth × 6–8 cm thick, for prawn broodstock with flowthrough (A) or recirculating (B) water system. (1) Seawater line, 5 cm PVC pipe, (2) 3.2 cm PVC pipe, (3) 20 cm PVC pipe (central standpipe for drainage), (4) 10 cm PVC pipe (for drainage), (5) 10 cm outlet pipe, (6) aeration line, 5 cm PVC pipe, (7) air-water lift, 5 cm PVC pipe, (8) rock and coraline sand substrate, (9) nylon netting, (10) GI wire No. 4, (11) welded wire, 6 mm mesh. Arrows indicate flow of water (from Primavera, 1983)

Appendix 1
ITINERARY

Appendix 2
PERSONS MET

Ms. Yang Lan and Ms. Yan Yu Kun accompanied the consultant for part and all of the local travel, respectively.