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					            Research, Development and Economics of
  Giant Freshwater Prawn (Macrobrachium rosenbergii) Culture
         in the Mekong River Delta, Vietnam: A Review


   Nguyen Thanh Phuong1, Vu Nam Son1, Tran Van Bui1, Nguyen Anh Tuan 1
                          and Marcy N. Wilder2

        1: College of Aquaculture & Fisheries, Can Tho University, Can Tho, Vietnam
                2: Japan International Research Center for Agricultural Sciences
                                  Tsukuba, Ibaraki 305-8686, Japan



Abstract

Giant freshwater prawn (Macrobrachium rosenbergii) has been considered one of the most important
species of freshwater aquaculture in Viet Nam, especially in the Mekong delta. With the widespread use of
hatchery-reared seeds, the production of farmed prawn has gradually increased since 2000 and reached
10,000 tons in 2002 (Ministry of Fisheries 2003). Prawn culture in Viet Nam is comprised of several
models such as integrated and alternative culture with rice on rice paddy, semi-intensive culture in ponds
and intensive culture in pen located along river/canal banks.
      Our research attempts during the last three years were to establish appropriate technologies for grow-
out of prawns in the Mekong River Delta via pilot researches and technical advises to local development
projects, and these efforts contributing to the rapid expansion of prawns culture in this delta. These studies
show that each culture model requires specific technologies for each ecological condition. The integrated
rice-prawn model is suitable for rice paddy where applying two rice crops, while the alternative rice-prawn
models are for annually flooded rice paddy and uncertain summer-autumn rice production areas. The river
pen culture model is practiced in deeply flooded rice paddy and along large rivers/canals. Studies from 28
integrated rice-prawn culture farms showed that the productivity varied with stocking density and stocking
size of seeds. Average productivity was 184 kg/ha (ranging from 42-566 kg/ha). Findings from 55
alternative rice-prawn culture farms in 2002-2003 showed that mean productivity of farms applying two
rice crops – one prawn crop per year was 358±201 kg/ha (ranging from 100-620 kg/ha) and of farms
applying one rice crops – one prawn crop per year was 924±262 kg/ha (ranging from 500-1500 kg/ha).
Similarly, a survey of 52 farms applying river pen culture model in 2003 presented that average



                                                      1
productivity was 412 kg/1,000 m2 (ranging from 125-1,100 kg/1,000 m2). The alternative rice-prawn and
river pen culture models perform the highest economic return and great potential to develop. They are
especially very well fitted to the national policy on agricultural re-structuring.


Keywords: Macrobrachium rosenbergii, freshwater prawn, alternative culture, integrated culture, river pen
           culture.


Introduction

Viet Nam with over one million hectare of freshwater bodies is high potential for inland aquaculture and
fisheries development. The aquatic production from freshwater bodies such as ponds, rivers, rice paddy and
reservoirs was 0.976 million tons in 2002 (corresponding 40.5 % of total national aquaculture and fisheries
production) (Ministry of Fisheries, 2003). The Mekong River Delta has a greatest potential for aquaculture
production because it has 641,350 ha of freshwater surface. Freshwater area of this region is potentially
extended by up to 1.7 million hectares during the flooding period (Sam, 2001 and Dien and Anh, 2001). In
the past, freshwater aquaculture was a subsistence sector that produced fish for local markets and home
consumption. However, some species have been farmed at commercial scales such as Pangasius catfishes
and giant freshwater prawn. Giant freshwater prawn is the only freshwater crustacean species having highly
commercial values, and has selected this species for culture in the freshwater water bodies such as rice
paddies, ponds and flooded areas (Ministry of Fisheries 1999). Giant freshwater prawn culture has been
planned to culture in an area of 32,000 ha and to achieve a production of 60,000 tons by the year 2010
(Decree No. 224/1999/QD-TTg.). Additionally, the Vietnamese Government has also implemented a new
policy called “re-structuring of agricultural production and its product consumption” (Decree No.
09/2000/NQ-CP) that allows the conversion of un-productive rice lands to aquaculture production, and this
will thus make the culture of M. rosenbergii more important to the nation’s aquaculture industry.
       In the past, most of commercial prawn culture models depended on prawn juveniles collected from
natural water bodies. Therefore, prawn culture remained fairly under-developed. Since 2000, Can Tho
University has become one of leading institutions in promoting researches and development of prawn seed
production (Phuong et al. 2003). The successfulness of different developmental projects on seed production
of M. rosenbergii from Can Tho University has played significant roles in establishing prawn hatcheries
and culture in Viet Nam. These contributed to the production of postlarvae and marketable prawns reaching
115 millions and 10,000 tons in 2002, respectively (Ministry of Fisheries, 2003).




                                                        2
Materials and Methods
This paper is prepared basing on the outcomes of two studies. The first study was researches conducted in
Vinh Long and Can Tho provinces under JIRCAS project and in Tra Vinh province under Department of
Science and Technology of Tra Vinh province project. These researches were focussed on the integrated
rice-prawn culture model. The second study was a recent survey on existing prawn culture models in the
Mekong river delta including alternative rice-prawn culture models (one rice crop and one prawn crop per
year and two rice crop and one prawn crop per year); and river pen culture model.
      The studies on integrated rice-prawn farming model were conducted in five farms in Vinh Long
province in 2000-2001 (Hai et al, 2001), three farms in Can Tho province in 2001-2002 (Phuong et al.
2002) and twenty farms in Tra Vinh province in 2000-2002 (Phuong et al. 2003). The survey was
conducted during September and October 2003 in An Giang and Can Tho for alternative rice–prawn culture
models and in Dong Thap for river pen farming model. There were forty two farms for one rice-one prawn
alternative culture model, thirteen farms for two rice–one prawn alternative culture model, and fifty three
farms for pen river culture model were surveyed. The survey was conducted using semi-structure
questionnaire. Technical, economical and related information such as strength, weakness, opportunity and
threats of the models were incorporated in the questionnaire.
      Collected data were analysed for average, standard deviation, maximum and minimum using excel
software.


Results and Discussion

In Vietnam, giant freshwater prawn culture was firstly initiated in the Mekong river delta because this
species is naturally distributed here. In past years, natural resources of prawn juveniles were rather
abundance; therefore prawn culture depended totally on wild collected seeds (Hien et al. 1998). More
recently, there has been a rapid decline in natural resources that greatly affects prawn culture development.
Fortunately, recently successful establishment of seed production techniques, trials on freshwater prawn
culture using hatchery-reared seeds were carried out. Different institutions in the Mekong Delta have been
implementing researches for the development of prawn culture. However, JIRCAS project has set-up
pioneer studies on the development of prawn culture focusing on rice-prawn integrated model. Latterly, the
College of Aquaculture & Fisheries of Can Tho has also involved in many other researches collaborated
with local authorities in prawn culture development. Research findings have gradually been introduced to
farmers, thus the prawn culture in this delta has rapid growth during the last few years and become
important practices of aquaculture industry of the Mekong delta regions.




                                                     3
Prawn culture on rice paddy
Culture of prawn on rice paddy is a traditional practice developed by farmers solely. Primary method was
very simple that was based totally on keeping prawn seeds recruited into farms via water gates by tides.
Prawns feed on natural food and were harvested together with the rice at harvest time. Since early 1980s,
some farmers have started to stock wild collected prawns in the rice paddy. Rice paddy was also better
designed and prawns were fed by-product such as trash fish, snail, etc. However, prawn culture on rice
paddy could not be expanded largely due to the shortage of wild prawn seeds. The recent successfulness of
prawn seed production from hatcheries has enforced a turning of prawn culture on rice paddy to a new
period that farmers started to use hatchery-reared postlarvae and culture technique has gradually improved
as well.


Integrated rice–prawn culture model
The cropping pattern of this model is two rice crops (summer-autumn and winter – spring) and one prawn
crop per year. Prawn culture is normally from April to December. This type of farming model is being
practiced in different regions of the Mekong delta where remaining two rice crops and low level of flood. A
summary of this culture model is presented in table 1. Farms were designed with surrounding trenches of
about 20-25 % of total rice paddy. Mostly, a part of the trenches was fenced with fine nylon net or built
with simple earthen dike for nursing prawn during the first period of stocking. After 3-4 weeks, prawns
reached sizes of 2-3 cm in body length and were ready for releasing into whole farm. At this point, rice has
already been sowed or transplanted. The production cycle of prawn was about 6-8 months, but prawns
stayed together with rice for about 2-2,5 months only. Stocking density ranged from 1.5-5 inds/m2
depending on seed sizes. Prawns were fed commercial pellets, fresh feeds such as golden snail, trash fish
and crab and home-prepared feeds during grow-out stage. Feeding rates varied according to growth stage of
prawns that were bout 2-10 % of body weight daily. Water was exchanged every two weeks at the spring
tide and kept above the rice paddy surface in accordance with the growing stages of rice.
       The productivity of this model varied widely according to stocking density and stocking size of seed;
and farm management regimes. The productivity was rather low ranging from 42-566 kg/ha that is due to
small sizes of prawn at harvest and low survival rate. This led to relatively low net return averaging 2.655
million VND/ha.


Alternative rice-prawn culture models
There are two models including one rice crop (winter-spring) and one prawn crop per year (namely
alternative model 1); and two rice crops (summer-autumn and winter –spring) and one prawn crop per year
(namely alternative model 2). The first model is that prawns are stocked in April and harvested in



                                                     4
Table 1: Technical and economical characteristics of integrated rice-prawn culture
 Description                                                         Mean (min-max)
 Farm areas (ha)                                                       0.37 (0.1-0.7)
 Trench areas (% of total farm area)                                     30 (20-55)
 Trench size (if there is): width and depth (m)                       2-3 and 0.8-1.2
 Seed sizes (g)                                              PL15 (0.01 g) or juvenile (0.6 g)
 Stocking density (prawn/m2)                                            3.17 (1.5-5)
 Feeding rate (% body weight – BW)                  According to growth stage and feeding diets, 2-10 %
 Culture period (months)                                                  6 (5-7)
 Culture season                                                     April to December
 Survival rate (%)                                                     22.9 (6.5-60)
 Harvest size (g/prawn)                                               36.1 (20.7-54.2)
 Productivity (kg/ha)                                                  148 (42-566)
 Total costs (million VND/ha)                                      4.635 (1.158-10.920)
 Net income (million VND /ha)                                       2.655 (-2.50-7.350)
* USD 1 = VND 15,000


December before then winter-spring rice crop started, while the second model is from July to December.
        This alternative model 1 has been being developed rapidly in the flooded areas, especially An Giang
and Can Tho provinces, where more than 350 ha operated in 2002. The rice paddy was re-designed by
leveling and widening surrounding dikes. A nylon net fence is required to install on the top of the dike to
prevent prawns from escaping during high flooding period. Hatchery-reared postlarvae were stocked
directly into the rice fields or in small nursing ponds for a month (Table 2). Stocking densities varied from
3-12 postlarvae/m2. Prawns were fed commercial pellets and fresh feeds. Commercial pellets were
normally used for the first two months, while the fresh feeds were for the following months. Fresh feeds
such as golden snail, trash fish and crab were rather cheap and abundance during the flooding period.
During flooding period (3-4 months), water usually flows over the surrounding dykes and farm could be
considered as over-flow water. After 6-8 months from stocking, prawns might reach sizes of 50-110 g in
body weight and were ready for entire harvest. Prawn productivity was 924 kg/ha in average (Table 3). Net
return was variable that might be from negative (lost) to very high values (Table 4). Prawns culture
contributed high portion (over 80 %) of total economic return from both rice and prawn.


Table 2: Characteristics of nursing area of alternative rice-prawn model (alternative model 1)
  No.                    Description                             Min-max (mean ± std)
 1         Total area (ha)                                        0.02-1.3 (0.28±0.28)
 2         Water depth (m)                                         0.8-1.2 (0.89±0.15)
 3         Nursing cycle (day)                                      10-55 (32.5±9.18)
 4         Sources of feed                                       Pellet and home-made




                                                     5
Table 3: Technical characteristics of alternative rice-prawn model - grow-out stage (alternative model 1)
  No.                      Description                              Min-max (mean- std.)
 1        Farm size (ha)                                              0.5-10 (2.93±2.35)
 2        Depth of ditch (from paddy surface) (m)                      0-1.5 (1.06±0.54)
 3        Water depth (above rice paddy surface) (m)                         0.9-2
 4        Sources of seed                                            Hatchery-reared seed
 5        Size of seed                                                      PL12- 15
 6        Stocking density (PL/m2)                                     3-12 (6.44±2.07)
 7        Prawn culture season                                         April–December
 8        Rice culture season                                      December – next April
 9        Feeding rate (%)                                              10-30 (18±8.37)
 10       Productivity (kg/ha)                                       500-1500 (924±262)
 11       Harvest size (g/prawn)                                        50-110 (62±42)


Table 4: Simple cost-benefits of alternative rice-prawn model (alternative model 1)
 No.      Item                                                       Min-max (mean±std)
          Prawn
 1        Total cost (million VND/ha)                                12.2-90.8 (42.0±19.2)
 2        Gross return (million VND/ha)                                0-113 (60.0±24.3)
 3        Income (million VND/ha)                                  - 32.9– 54.7 (21.0±20.5)
          Rice
 4        Total cost (million VND/ha)*                                  1-10 (4.71±1.90)
 5        Gross return (million VND/ha)                                6-12.4 (9.05±1.78)
 6        Income (million VND/ha)                                    -0.7-8.15 (4.34±1.98)
 7        Grand total income                                        - 29.2-59.1 (25.3±20.7)
* USD 1 = VND 15,000


      The alternative model 2 remains two rice crops (summer-autumn and winter-spring rice). Prawns are
stocked into rice paddy when the summer-autumn rice is harvested. This model is suitable for areas of high
flood level such as in An Giang, Can Tho and Dong Thap provinces. Detail descriptions of this model are
presented in tables 5, 6 and 7. The survey showed that this model was operated about 5-6 months, therefore
stocking of large size seeds (averaging 14±4.26 g/animal) was required in order to ensure the harvest
prawns reached marketable sizes. The productivity of prawns in this model (averaging 358 kg/ha) was
much lower than the alternative model 1 (averaging 924 kg/ha). However, the harvest size of prawns was
85 g in average, which was much big than 62 g of the alternative model 1. This harvest size reached the
market price of VND 120,000/kg compared to VND 70,000/kg of the alternative model 1.




                                                     6
Table 5: Technical characteristics of alternative rice-prawn – grow-out stage (alternative model 2)
 No.                  Description                                  Min-max (mean- std.)
 1      Total farm size (ha)                                       0.13-1.25 (0.68±0.39)
 2      Depth of ditch from paddy surface (m)                       0.5-1.6 (0.93±0.42)
 3      Water depth (above paddy surface) (m)                       0.5-1.6 (0.93±0.42)
 4      Sources of seed
        • Hatchery                                                          25%
        • Wild seed                                                         75%
 5      Sizes of seed
        • Hatchery-reared seed                                             PL12-15
        • Wild seed                                                5-20 g/seed (14±4.26)
 6      Stocking density (ind./m2)                                    1-16 (2.51±4.42)
 7      Stocking time                                 1 for hatchery-reared or multi-stocking for wild
                                                                            seed
 8      Prawn culture season                                           July–December
 9      Rice culture season                                        December – next June
 10     Feeds                                               Farm-made (75%) and pellet (25%)
 11     Feeding rate (%)                                                    5-30
 12     Productivity (kg/ha)                                        100-620 (358±201)
 13     Harvesting size (g/prawn)                                   10-250 (85.3±48.1)


Table 6: Simple cost-benefits of alternative rice-prawn (2 rice and 1 prawn)
 No.                         Item                         Min-max (mean- stdev.)
        Prawn
 1      Total cost (million VND/ha)                                   1.15-26 (13.6±7.61)
 2      Gross return (million VND/ha)                                   7-55 (31.4±17.8)
 3      Income (million VND/ha)                                       3.5-42.7 (17.8±12.6)
        Rice
 4      Total cost (million VND/ha)                                  0.25-9.00 (5.69±2.86)
 5      Gross return (million VND/ha)                                 3.5-42.7 (17.8±12.6)
 6      Income (million VND/ha)                                        1.6-15 (11.0±4.10)
 7      Grand total income (rice and prawn)                          7.87-55.0 (28.8±14.1)
* USD 1 = VND 15,000


River pen culture of fresh water prawn
Prawn culture in pen is a traditional practice of the farmers in Dong Thap province. There were 1,516 pens
in operation in this area in 2002. Pens were located along the river banks, that are canals or sub-branches of
the Mekong rivers having 30-50 m wide and 5-7 m deep. Water current, water quality, soil quality and
water depth were of the main criteria for consideration and selection of pen sites. Pens were made of
bamboo, wood and nylon net. Pens had a site of 4-20 m wide (average of 8.5 m), 7-50 m long (average of
23.2 m) and 2-4.5 m deep (average of 3.2 m). Presently, most of pens (96,1 %) are stocked with wild
collected prawn seeds (2.82 g/animal). Hatchery–reared seeds were rarely stocked due to small size and not
possible to reach marketable size at harvest. Prawns were stocked 1-3 times per crop at density 61 ind/m2.




                                                      7
Prawns were fed with home-made feed prepared from trash fish, golden snail, paddy crabs, coconut, rice
and/ or cassava at feeding rates of 9-50 % body weight daily.
       After 4 month of culture, prawns were partially harvested for the large ones. Normally, prawns were
harvested 2-4 times before final harvest conducted. Average productivity was very high of 522 kg/1,000
m2. Average survival rate was 23 %, and body weight reached to 60.7 g in average. Average net income
was 10.7 million VND/1,000 m2.


Table 7: Technical characteristics of pen culture in river
 No.                    Description                                Min-max (mean- stdev.)
 1      Total pen size (m2)                                          35-900 (209±168)
 2      Water depth (m)                                               2.3-4.5 (3.2±0.5)
 4      Source of seed
        • Hatchery (%)                                                       3.80
        • Wild seed (%)                                                      96.2
 5      Size of seed
        • Hatchery (day)                                                     PL30-60
        • Wild seed (g)                                                       2.82
 6      Stocking density (ind./m2)                                       9-278 (62±47)
 7      Stocking time                                                           1
 8      Culture season                                                 June to December
 10     Feeds                                                             Farm-made
 11     Feeding rate (%)                                  22 (73 % farms) and ad-libitum (27 % farms)
 12     Productivity (kg/ha)                                         142-1,571 (522±333)
 13     Harvest size (g/prawn)                                          25-90 (60.7±13)


Table 8: Simple cost-benefits of pen river culture (million VND/1,000m2)
 No.                        Item                                     Min-max (mean- std.)
 1      Total cost                                                     6-68.6 (27±13.8)
 2      Gross return                                                 10.5-110 (37.7±23.4)
 3      Income                                                      -18.7-65.5 (10.7±17.3)


General discussion about the development of prawn culture in Viet Nam
Recently, integrated and alternative rice-prawn culture and river pen culture of prawns are main practiced
models in the Mekong delta. The integrated rice-prawn culture model has large areas for future
development and can be considered as a subsistence activity, which brought additional incomes to the rice
production. This type of culture is more suitable for non-flooding areas or where still remains two crops of
rice per year. However, this model achieves low productivity, small prawn size at harvest, low survival
rate, etc. causing low economic return if compared to other models (Table 9).
       The two alternative models are more commercial and becomes a central activity of rice farmers.
These models are suited for flooded areas or when the summer-autumn rice cultivation is subjected to high
risks of flood. Many provincial Governments of the Mekong river delta have planned to expand the


                                                      8
alternative rice-prawn in the coming years. The advantages of these models are high economic returns and
suitability to rice paddy ecology. However, these models need high investment and technologies, which
may not suitable for poor and low skill farmers. The economic return of these models is very attractive that
creating a movement of development in the coming years.
        Prawn culture in pens is also an importantly economic activity, especially in the region located
upstream and close to Mekong River or large of creeks and canal. However, this is considered as intensive
culture and is thus need a high investment in capital and techniques. Several constraints arisen from this
model such as a need of improvement of culture techniques, variation of water quality, diseases outbreak,
lack and poor quality of wild seed, lack of capital, etc.
        The simple comparison of four studied models is presented in table 10. This shows that the
alternative and river pen culture models have the highest economic return. However, each prawn culture
type has a number of strengths, weaknesses, opportunities and threats (Table 10). These issues need careful
further analysis for proper utilization of strengths, exploitation of opportunities and solving of weaknesses
for sustainable development.


Conclusion

In conclusion, with significant supports from research institutions as well as from central and local
organizations, the culture industry of fresh water prawn in Vietnam is now developing very rapidly. The
development of the industry has play important role in improving social-economic of the farmers and
contributing to national export values. Prawn culture has large water bodies for future development;
however, there are still several constraints that need appropriate solutions and development strategies.




Table 9: Technical and economical characteristic of various prawn culture models
                                             Rice – prawn models                     Pen culture
 Item                             Integrated              Alternative
                                              1 rice-1 prawn     2 rice-1 prawn
 Farm size                           0.37           2.93               0.68                 209
 (ha)                             (0.1-0.7)       (0.5-10)         (0.13-1.25)           (35-900)
 Stocking density                    3.17           6.44               2.51                  62
 (seed/m2)                         (1.5-5)         (3-12)             (1-16)              (9-278)
 Productivity                        148            924               358.2                5,220
 (kg/ha)                          (42-566)      (500-1,500)         (100-620)         (1,420-15,710)
 Total cost                          4.64           42.0              13.61                 270
 (million VND/ha)                (1.16-11.2)    (12.2-90.8)        (1.15-26.0)           (60-686)
 Net income                          2.66           21.0               17.8                 107
 (million VND/ha)                (-2.5-7.35)    (-32.9-54.7)        (3.5-42.7)          (-187-655)
 Negative net return (%)             28.5           11.9                 0                   27


                                                       9
Table 10: The SWOT analysis of prawn culture in the Mekong delta, Viet Nam
 Strengths       1.   Large culture areas including rice paddy, pond and river bodies
                 2.   One of important species defined for freshwater aquaculture development
                 3.   Increasing seed supply from hatcheries
                 4.   Improvement of technologies for seed and grow-out production

 Weaknesses      1. Under-supply of hatchery-reared seeds and reduction of wild seeds
                 2. Mainly back-yard hatcheries and under-development of hatcheries network
                 3. Low level culture technologies and small-scales
                 4. Market limitation, mostly domestic markets
                 5. Un-stabilized market prices of table prawn

 Opportunities   1.   Possible to diversify markets (including international and domestic)
                 2.   Possible to expand culture areas to flooded rice paddies
                 3.   Creation of job and improvement of incomes for small-scale farmers
                 4.   Diversification of farmed species

 Threats         1. Competition for international markets with other countries (China, Thai land)
                 2. Possible competition of culture areas with white leg shrimp (Penaeus vannamei)?


Acknowledgments

This paper was prepared based on a number of research projects funded by College of Aquaculture and
Fisheries – Can Tho University, Japan International Research Center for Agricultural Sciences (JIRCAS)
and Department of Science and Technology of Tra Vinh province.


Literature Cited

Decree No. 09/2000/NQ-CP (2000). Re-structuring of agricultural production and its products
      consumption, 8 pp. (in Vietnamese).
Decree No. 224/1999/QD-TTg. (1999). Approval of aquaculture development plan period from 1999-2010,
      6 pp. (in Vietnamese).
Dien, H.T. and N.N. Anh (2001). Study on flood, flood forecasting and flood control in the Mekong delta,
      Viet Nam. Paper presented at the scientific workshop on Environment and Disaster in the Mekong
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Hai, T.N., T.T.T. Hien, D.H. Tam, V.T. Toan, N.T. Phuong and M.N. Marcy. Culture of freshwater Prawns
      (Macrobrachium rosenbergii) in rice-fields using hatchery reared postlarvae in Tam Binh district,
      Vinh Long province. Proceeding of the 2001 annual workshop of the JIRCAS Mekong delta project
      on development of new technologies and their practice for sustainable farming systems in the
      Mekong delta at Can Tho University.



                                                   10
Hien, T.T.T., T.H Minh, N.T Phuong and M.N. Wilder (1998). Current status of freshwater prawn culture
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Tóm tắt

Tôm càng xanh (Macrobrachium rosenbergii) đã được xác định là đối tượng nuôi nước ngọt quan trọng ở
Việt Nam, đặc biệt là ở Đồng Bằng Sông Cửu Long (ĐBSCL). Nhờ ngày càng sử dụng rộng rãi tôm giống
nhân tạo nên sản lượng tôm nuôi tăng nhanh từ năm 2000 và đạt sản lượng khoảng 10.000 tấn năm 2002
(Bộ Thuỷ sản 2003). Tôm càng xanh ở Việt Nam hiện đang được nuôi với nhiều mô hình khác nhau như
nuôi kết hợp và luân canh với trồng lúa, nuôi bán thâm canh trong ao và nuôi thâm canh trong đăng quần
ven sông.
       Các nghiên cứu của chúng tôi trong ba năm qua với mục tiêu là cố gắng xây dựng các qui trình kỹ
thuật nuôi tôm càng xanh phù hợp cho ĐBSCL thông qua các thực nghiệm và các tư vấn kỹ thuật cho các
dự án phát triển nuôi tôm ở các địa phương. Với sự cố gắng đó chúng tôi đã đóng góp xứng đáng vào sự



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phát triển nhanh chóng của nghề nuôi tôm càng xanh ở vùng ĐBSCL. Kết quả của các nghiên cứu cho thấy
mỗi mô hình nuôi đòi hỏi các kỹ thuật đặc thù phù hợp với các điều kiện sinh thái cụ thể. Mô hình nuôi tôm
kết hợp với trồng lúa phù hợp với những vùng canh tác hai vụ lúa, trong khi đó mô hình nuôi luân canh
tôm-lúa thì phù hợp cho những vùng ngập lũ hàng năm và vùng mà canh tác lúa Hè-Thu nhiều rủi ro do lũ.
Nuôi tôm đăng quần thì được thực hiện chủ yếu ở vùng ruộng ngập lũ sâu hay ven sông. Nghiên cứu 28 hộ
nuôi tôm-lúa luân canh cho thấy năng suất tôm biến động theo mật độ và kích cỡ giống thả. Năng suất
trung bình là 184 kg/ha (dao động 42-566 kg/ha). Kết quả điều tra 55 hộ nuôi tôm-lúa luân canh năm 2002-
2003 cho thấy năng suất trung bình của các hộ canh tác hai vụ lúa - một vụ tôm mỗi năm là 358±201 kg/ha
(dao động từ 100-620 kg/ha) và của các hộ canh tác một vụ tôm - một vụ lúa là 924±262 kg/ha (dao động
từ 500-1500 kg/ha). Tương tự, kết quả khảo sát 52 hộ nuôi tôm đăng quần ven sông năm 2003 cho thấy
năng suất đạt 412 kg/1,000 m2 (dao động từ 125-1.100 kg/1.000 m2). Mô hình nuôi luân canh tôm-lúa và
tôm đăng quần là những mô hình có hiệu quả kinh tế cao nhất và nhiều tiềm năng phát triển. Những mô
hình này rất phù hợp với chủ trương của nhà nước về chuyển dịch cơ cấu trong nông nghiệp.




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Description: Research, Development and Economics of Seed Production of Giant Freshwater Prawn Macrobrachium Rosenbergii a Review document sample