Environmental rapid assessment in the break-out shrimp diseases of Baclieu province, Mekong delta, Vietnam

DFID/CRF Project
“Accelerating poverty elimination through sustainable resource management
in coastal lands protected from salinity intrusion”
April 2000 – March 2003

Environmental Rapid Assessment
In the break-out shrimp diseases
of Baclieu province, Mekong delta, Vietnam

Duong Tri Dung - Le Anh Tuan

Paper presented at
the Mid-term Review Workshop in Bac Lieu
June 2002

University of Newcastle/University of Cantho/ICLARM
Department of Agriculture & Rural Development, BacLieu Province, Vietnam

i


CONTENT
Abstract........................................................................................................................................................................................2
I. Introduction ................................................................................................................................................................................2
II. Methodology..............................................................................................................................................................................4
1. Sampling sites.........................................................................................................................................................................4
2. Data collection.......................................................................................................................................................................4
a. Physical and chemical samples. ..................................................................................................................................... 4
b. Plankton.............................................................................................................................................................................. 4
3. Analyzing methods.................................................................................................................................................................5
a. Chemical analyzing .......................................................................................................................................................... 5

b. Plankton analyzing ........................................................................................................................................................... 5
4. Data analyzing........................................................................................................................................................................5
III. Result and discussion ............................................................................................................................................................6
1. The physical water quality in the shrimp ponds...............................................................................................................6
2. The chemical water quality in the shrimp ponds..............................................................................................................7
a. Dissolve oxygen................................................................................................................................................................ 7
b. H2 S ...................................................................................................................................................................................... 7
c. Total iron ............................................................................................................................................................................ 7
d. Concentration of NH4 + ..................................................................................................................................................... 7
e. Concentration of NO3 - ...................................................................................................................................................... 8
f. PO4 3-..................................................................................................................................................................................... 8
g. COD. ................................................................................................................................................................................... 8
3. The biological water quality in the shrimp ponds............................................................................................................8
a. Phytoplankton.................................................................................................................................................................... 8
b. Zooplankton..................................................................................................................................................................... 10
4. The reason of the disease breakout...................................................................................................................................11
a. The knowledge of farmers on shrimp culture ............................................................................................................ 11
b. The popular current methods of shrimp cultivation.................................................................................................. 12
c. Planing for sustanable of shrimp cultivation.............................................................................................................. 13
IV. Conclusion ..............................................................................................................................................................................14
Recommendation .........................................................................................................................................................................14
Reference........................................................................................................................................................................................14
Appendix........................................................................................................................................................................................15
Annex 1. physical and chemical water quality.....................................................................................................................15
Annex 2: PHYTOPLANKTON ...............................................................................................................................................16
1. Taxa........................................................................................................................................................................................16
2. Density (cell/ml)...................................................................................................................................................................18
Annex 3: ZOOPLANKTON (ind./L)......................................................................................................................................19

ii

Environmental Rapid Assessment
the break-out shrimp diseases
of Baclieu province, Mekong delta, Vietnam
DuongTriDung(1), LeAnhTuan(2)
Abstract
To understand what are the main reasons to cause the disease and dead off on the marine shrimp
culturing system in Mekong coastal areas, the survey on 14 sites was carried out in five hamlets
of Baclieu province. The physical, chemical and plankton factors in the groups of water body
such as dead shrimp ponds, stronger shrimp ponds and water supplied systems were sampled.
After analyzing, it showed that the water pH, temperature and salinity gradient in dead shrimp
ponds is higher and than other water bodies. The concentration of H2 S and NH4 + is too high to
tolerance of shrimp. Phytoplankton and Zooplankton component indicated the pollution of
organic matter and high gradient in water quality.
To resolve these problems, it is necessary to provide the best knowledge on shrimp culture to
farmers and correcting the flow-in or flow-off system in the far-off areas. It is also important to
growth up the aquatic plant in the extensive shrimp culture system.
I. INTRODUCTION
Shrimp culture is a high income farming system but the risk of that activity is not small.
The economic effect and income from the shrimp culture is many times higher than rice
cultivation so the farmer in the coastal area or saline water decide to change the rice fields into
shrimp pond. It is not only culture shrimp in the brackish water but also culture tiger shrimp in
the salinity instruction that is planned to expand rice field.
According to the report from the coastal provinces of Mekong delta, until February 2002,
the shrimp farmers stocked on 2/3 total shrimp culturing area. Especially, In Camau, They were
stocked about 92% of shrimp culturing areas of province (202000 ha). The main techniques were
applied for shrimp culture are improve-extensive and semi- intensive, the areas of intensive
culture is about 5% - 6%. The numerous of stocking shrimps were imported from the provinces
of central of Vietnam as Nhatrang, Ninhthuan, Binhthuan, Danang, there is only a little of larva

that were produced at the local areas.
The break out of disease appeared in Bentre, Tiengiang, Soctrang and Anbien
(Kiengiang). The diseases of shrimp were found after 30 until 45 days of stocking. In Baclieu
and Camau, the diseases were found after 40-60 days after stocking. Only in Vinhthuan
(Kiengiang) diseases of shrimp were found after 60-70 days of stocking. The area found shrimp
disease is about 30-60% of shrimp culturing area of Mekong delta provinces.
(1)
(2)

College of Agiculture – Cantho University
College of Technology – Cantho university
2


The syndromes of shrimp disease were diagnoses are red body, white spot. As the testing
result of Camau province, 31 samples of larva at Ngochien and Cainuoc, 100% of them were
infected of WSSV (Testing from the sub-institute of aquaculture research II). In Ngoctu
(Myxuyen - Soctrang), the market size shrimps that were infected WSSV are 50% (7/14 ponds
tested). 30,76% of the stocking shrimp (PL 12-20) that were imported from the central of
Vietnam were infected WSSV (4/13 m?u). In Bentre, the ratio of WSSV shrimp is low, 10% of
the sample were infected white spot, and 13.3% of them were infected of red body (Results of
Center of Aquaculture extension, they analyzed by PCR with modern machine).
From the current big risk of shrimp culture, many of governmental levels, local
departments and also scientists were carried out the survey to look for the reason why the disease
break out in the whole coastal province of Mekong delta this time. There are many trends were
investigated and supplied many reasons.
(i) The needs of shrimp larvae for stocking is higher than supplement so the shrimp
hatcheries try to produce the more number than capacity with the less quality (as more
reproduction than effort), event thought the shrimp profile were not correct when being asked
about the price of larvae. Then the low qualitative seed could not stand by the high gradient of

the environmental factors. It is easy for the disease to infect.
(ii) Being worry about the lack of seed, many of shrimp farmers stocked before
traditional New Year. At that time, the weather and environment parameter were not suitable, the
shrimp were stress and dead. Practically, the gradient of temperature is too high between day and
nighttime (daytime 32o C - 33o C, nighttime 22o C - 23o C). On the other hand, shrimp were sock by
the salinity changing due to the affect of tidal, example the salinity in the shrimp pond is about
30‰, It will be very low when the tide flow in.
(iii) Re ally, some shrimp culture areas of Baclieu, Camau, Soctrang were not enough
water supplied for the shrimp ponds so they have to be going the season late and not to treat the
culture system when necessary. On the intensive culturing areas, the waste treatment systems
were not complete so that pollution will be developed after 2-5 years of culture. There is not
enough natural food for shrimp at the first stage of culturing period; they could not develop well
in the next. In the adding, the management of water quality as DO, NH3 , pH, water temperature,
feeding, health of shrimp ... were not interested well.
Following the risk of the coastal province of Mekong delta, Baclieu was not out of the
affect of the death of shrimp so that the provincial government decided to look for the reason
why the disease break-out. Getting the agreement of Baclieu Provincial People Committee,
Cantho University, Department of Agriculture and Rural Development, Department of fishery
co-operate to survey for “Environmental Rapid Assessment” with the analyzing of physical,
chemical and plankton factors.
We thank to the budget from IRRI and the agreement of local government that help us
getting the samples in the correct sites and correct times.

3


II. METHODOLOGY
The shrimp diseases were found in every district that has the shrimp farms. Particularly,
100% of the shrimp ponds of some village was not harvested. The survey was carried out in the
salinity intrusion to get the main cause and the control was the shrimp ponds out of the project

area.
The survey was done in a day (14/3/2002).
1. Sampling sites
In the salinity intrusion, 3 villages were chosen for survey, they are Phongthanh,
Ninhthanhloi and Phuoclong. Longdien was the control village where is out of the project are.
In every hamlet of those villages, samples were get in 3 conditions of the shrimp ponds,
they are death shrimp ponds, strong shrimp ponds and the canal that supplied water for the whole
shrimp ponds of that hamlet. The situations of every sample were showed under.
- In hamlet 19 and 23 of Phongthanh: 6 samples
- In hamlet Phuocthohau of Phuoclong: 3 samples
- In hamlet Chuchot of Ninhthanhloi: 3 samples and
- Hamlet Daidien of Longdien: 2 samples, without the strong shrimp pond.
2. Data collection
a. Physical and chemical samples.
- Water temperature, pH, salinity, and DO were measure immediately at the sampling site
by field data collection machines.
- Taking 1 L of sampling water and keeping at 4o C by cover with ice. They were
transferred to Cantho University for analyzing; it is not longer than 48 h after sampling. The
parameters were checking are total iron, H2 S, NH4 +, NO3-, P-PO4 3- and COD.
b. Plankton
- Using plankton nets with the mesh size are a = 25 µ and 59 µ for selecting of
phytoplankton and zooplankton (respectively). Qualitative samples were selected by filtering the
large volume of water at the sampling sites; the more volume is the more exact. Quantitative
samples were selected by filtering 100L of sampling water. They were preserved by formalin
(2%).
All of them were transferred to Cantho University and analyzed there.

4

3. Analyzing methods
a. Chemical analyzing
- Water temperature and DO were measured by Oxy 330/SET at the sampling site
immediately.
- pH were checked by pH 330/SET-1
- Turbidity was definite by Orbeco analytical systems
- Salinity was measured by EC 4320
- H2 S, Fe, COD, NH4 +, PO 43-, NO 3-: were analyzed in the laboratory of College of
Technology using the popular method that were presented in the hand book Standard
Methods, 1995.
b. Plankton analyzing
- Identifying the name of plankton by microscope with the magnetic 100 – 400x,
comparing with plate of the books.
- Counting the density of phytoplankton by the improve blood cell, calculating the
x.1600.a
number with the function d =
where d: density of phytoplankton (cell/ml); x : number
16.5.c.v
of phytoplankton after three time counting (cells); 1600: the small areas of the counting cell; 16:
the small areas in a large areas; there are five large areas; c: the volume of sampled were taken
out for counting (ml); a: total volume of sample after concentration (ml); v : total volume of water
that taken for sampling (ml)
a
1000 where d: density
v
of zooplankton (ind./m3 ); a number of zooplankton individual that were sampled, using Bogorov
counting cell (ind); v: the total volume of sampling water (litter).

+ Calculating density of zooplankton by using the function: d =

4. Data analyzing
- Standard deviation were calculated from the many samples, comparing the STD of each
group together.
- Explaining the cause of the different between water boy group, looking for the way to
solve those problems.

5


III. RESULT AND DISCUSSION
1. The physical water quality in the shrimp ponds
There is a lot of difference between the water body groups about the physical water
quality, which was displayed on the table 1. The difference of each parameters were not same,
that is depend on the structure of the shrimp ponds.
Table 1: The variety of the physical parameters in the shrimp ponds.
Death/disease shrimp ponds

Strong shrimp ponds

Notes

Temperature (o C)

27 – 33

29 – 31

1 time per each

pH

6.2 – 9.5

6.3 - 8.5

Salinity (o /oo )

20 – 30

21.2 – 27.1

Turbidity (NTU)

18 – 55

6.9 – 45

Convert from EC

Temperature: the varieties of temperature from the morning until the evening were high
in the shrimp pond, both for weakness and strong shrimp ponds. Comparing together, the
temperature gradient in the weakness shrimp ponds were higher than strong shrimp pond (6 and
2o C, STD = 1.81 and 1.07, respectively). For the both shrimp ponds, the range of the temperature
were not out of the tolerance of the shrimp but practically, the gradient of the temperature in the
weakness shrimp ponds are too high to make the stress for the shrimp then they could not
stronger than the affect of the disease. It may be the cause to break out of the disease.
The gradients of the temperature in the shrimp ponds were high because the covers in
these ponds are not enough. There are two reasons: (i) water level in the shrimp ponds were not
high enough and (ii) there are not enough cover as grass or plant to limit the sun light directly
going into the ponds. It is necessary to make the cover for the shrimp ponds by integrating

between shrimp and rice or forest in the improved extensive system or improve the water level in
the semi- intensive system.
pH: It is also same the way of temperature, the gradient of pH in the weakness shrimp
ponds were higher than in the strong shrimp ponds (3.3 and 2.2; STD = 1.08 and 0.73,
respectively). The gradient of pH depends on the process of photosynthesis of phytoplankton,
clearly it is belong to the light and plankton density. Another reasonably, some shrimp farmers
did not improve the ponds well then phytoplankon and periphyton developed to cause the high
gradient of pH.
Salinity: The varieties of salinity in the weakness shrimp ponds were higher than the
strong ones. It is able that the farmers exchanged the water when they look for the disease
developed on the ponds or the high temperature increased salinity of the low water level ponds.
The gradient of the salinity were 20 – 30 ppt (Std = 3.72) and 21.2-27.1 ppt (Std = 2.02) in the
weakness and strong shrimp ponds. The range of salinity of both group ponds were not out of the
tolerance of shrimp but the large gradient could be the cause of the stress for shrimp, particularly
they were the weakness shrimp ponds.
6


Turbidity: in the shrimp ponds, the water was kept stagnant so the values of turbidity
were not high. The cause of the turbidity could be sediment, suspended organic matter and
plankton but the high density of plankton could be the main affect to turbidity in the lentic water
body so it could be the high density of plankton cause the effect to shrimp culture systems.
Strong shrimp pond
Weakness shrimp pond

30.0

30.0

Strong shrimp pond

Weakness shrimp pond

25.0

20.0
Salinity (ppt)

Temperature (oC)

40.0

10.0
0.0

20.0
15.0
10.0
5.0
0.0

10.0

Strong shrimp pond
Weakness shrimp pond

50.0

Strong shrimp pond
Weakness shrimp pond

Turbidity (NTU)

pH

8.0
6.0
4.0
2.0
0.0

40.0
30.0
20.0
10.0
0.0

Fig. 1: The variety of the physical parameters of the shrimp pond groups
2. The chemical water quality in the shrimp ponds
Some chemical parameters were analyzed such as DO, H2 S, total iron could be explained
the cause of the disease appeared in the whole coastal areas of Mekong delta. Table 2 showed
the range of these factors. Some parameters as total iron, COD were too high for the tolerance of
shrimp to live, both of the shrimp pond groups are similar. It could be interpreted by the mix of
the whole of ion in the water, they reduced their toxic to organism. After analyzing the reason
why they appear, it is easy to control them.
a. Dissolve oxygen
The ranges of DO were not out of the tolerance of shrimp because of the large water
surface, that made easy for the oxy from the air diffuse into water. It is not limit factor for shrimp
culture, (2.23-5.7 ppm and 2.56-5.2 ppm in the weakness and strong shrimp ponds).
7

Comparison the DO of each pond, it could be seem in a pond with different sampling
time, then it did not explain the cause of the affection.
Table 2: The range of chemical parameter of the shrimp pond groups.
Weakness shrimp pond

Strong shrimp pond

Notes

DO (ppm)

2.23 – 5.7

2.56 - 5.2

Oxymeter

H2 S (ppm)

0.96 – 1.6

0.88 – 1.76

photospectrometer

Total iron (ppm)

7.99 – 23.5

5.23 – 17.88

Photospectrometer

NH4 + (ppm)

0.24 – 1.48

0.32 – 2.12

Photospectrometer

NO3 - (ppm)

0.22 – 1.08

0.51 – 0.98

Photospectrometer

PO4 3-(ppm)

0.01 – 0.23

0.01 – 0.15

Photospectrometer

COD (ppm)

288 – 608

272 – 520

Cr2 O7

b. H2 S
The concentrations of H2 S were very high but there are not significant different between
two groups of shrimp pond (0.96-1.6 ppm and 0.88-1.76 ppm in the weakness and strong shrimp
ponds).
This is the toxicant, it appear when the low oxygen of water. Particularly, the high
density of lab- lab could be causing the low dissolve oxygen. To limit the high concentration of
H2 S, it is necessary to improve the shrimp pond before stocking.
c. Total iron
All of the chemical elements that showed on the table 2, the concentration of total iron is
too high to shrimp alive. Their ranges were 5.23-23.5 ppm. It is necessary to separate into the ion
2+ and 3+ of total iron because the harm was cause of the 2+ iron.
The high concentration of total iron could be easy to change from 3+ into 2+ and vice
versa so the shrimp pond always get the risk of high ion 2+ of iron when the dissolve oxygen is
low in the pond. To reduce the iron go into the shrimp pond, It should be to make the reservoir to
keep the seawater some days before flow into the shrimp pond. Aerating water of the reservoir or
supplying the chemical when necessary is to oxydazate iron to release it out of water so water
would be better for cultivation.
d. Concentration of NH4 +
Concentrations of NH4 + were high in both of the shrimp pond groups. Their ranges were
about 0.24-1.48 ppm and 0.32-2.12 ppm in the weakness and strong shrimp ponds.

7

The high concentration of ammonium ion would increase the density of phytolankton and
other plant, especially the development of lab- lab. They could make the high gradient of the pH,
DO, biogen... Being able reduce them by clean pond before stocking season.
e. Concentration of NO3The concentrations of nitrate were not high, their range are not out of the tolerance of
shrimp. They are 0.22 – 1.08 and 0.51 – 0.98 ppm in the weakness and strong shrimp ponds.
Their ranges are not significant different for both shrimp pond groups so it could say that it is not
the main factor to cause the shrimp disease.
Nitrate and ammonium could be exchanged together, the more concentration of NH4 +
when the pond is less of oxygen. So it could cooperate with Do and other factors to affect the
heath of shrimps.
f. PO43The concentration of this factor is stable by the absorbing of the mud so it is about 0.010.23 ppm and 0.01-0.15 ppm in the both groups (weakness and strong shrimp ponds,
respectively).
In the areas that are low pH or acid sulfate soil are necessaries to supply phosphate
inorganic fertilize to increase pH.
g. COD.
COD of the shrimp ponds were too high, they are 288-608 ppm and 272-520 ppm
(weakness and strong shrimp ponds). These concentrations were not real showing the oxygen
need by the organic matter because of there is a lot of ions in the salt water need oxidization.
After analyzing, the results tell that should make the reservoir for taking out the
oxidization ions. They could reduce DO of the pond to be harm for shrimp particularly in the
early morning.
3. The biological water quality in the shrimp ponds
The aquatic organism were the indicators for the water quality, they can exist due to their
tolerance. Distribution of plankton could show characteristic of physical and chemical
environment. There is one time of getting sample for rapid assessment of environment is not
enough if biological samples were not assessed.
a. Phytoplankton
There were 33 taxa of phytoplankton identified, the abundant is diatom. The
dinoflagenlate was poor with 2 species found. Their distributions depend on the climate of the
year and the environment of the pond. One time of sampling with 14 sites is not enough data to

8


tell that is the whole alga of these areas but their dominant could tell the water quality of the
pond.
The phytoplankton components were not same in each water bodies, The number of taxa
of each pond group was showed on the table 4. The diversity of phytoplankton was found in the
strong shrimp ponds.
Table 4: The variety of number of phytoplankton taxa in each shrimp pond groups
Water supply system

Weakness ponds

Strong ponds

Number
of species

Ratio
%

Number
of species

Ratio
%

Number
of species

Ratio
%

Diatom

12

70.58

9

69.23

12

60.00

Blue-green algae

02

11.76

4

30.77

05

25.00

Green algae

01

05.88

03

15.00

Dinoflagelates

02

11.76

Total

17

13

20

Looking on the table 4, it showed that diatom were the most abundant with 12 taxa (60%
of total of strong shrimp ponds) but in the weakness ponds, there are only 9 taxa of Diatom get
69.23% of total of weakness group. So they could tell that the diversity of strong group is higher
than the weakness group, then it could tell the more diversity is the more stable of environment.
On the other hand, the diversity of diatom showed the relationship between the canal and the

ponds, the higher diversity is the more water exchange.
The blue –green algae is abundant in the poor nutrient and unstable environment ponds
because the high tolerance of blue green algae. There are not significant different between two
groups of shrimp pond, but the lower diversity could tell the higher of risk in the pond.
The dinoflagelates also were found, they are the indicators of the organic pollution of
water bodies. They can cause the death of shrimp by their toxic. At Ninhthanhloi village, the
farmer kept the haline water in the pond for culturing shrimp in the whole year, the water could
not refresh then it is easy polluted. On the other hand, They wanted to farm the tiger shrimp in
the low salinity water bodies in the rainy season. These ways made the pollution happen. After
all, the dinoflagellates could develop and dispense to cause the death for the whole area.
Normally, the green usually appears in the freshwater, some of them could develop in the
low salinity waterbodies. These cooperate with blue green alga to make the lab- lab which cause
the harm for the shrimp pond as explained above. The process of improve the shrimp pond
should be necessary to limit the development of lab- lab.
After analyzing, it showed that density of phytoplankton was not high, Their ranges are
400-39600 cell/ml. The variety of phytoplankton density is high in the canal because the
structure of each area. In Daidien and Chuchot canals, densities of phytoplankton are high
9


because the farmers transferred a lot of waste water from the shrimp ponds to canals. The high
density of phytoplankton from the pond could cause the high density in the canal.

Density (cell/mL)

In the both shrimp pond groups, densities of phytoplankton were not high, they are about
400-2800 cell/ml and 1600-11200 cell/ml in the weakness and strong shrimp ponds. The density
of phytoplankton were not significant different but the ratios of blue green algae were higher
than 50% in the weakness shrimp ponds. The dominant of blue green algae increased the risk
because these algae could develop well in the ponds, which are poor water quality.

35000

Weakness

30000

Canal
Strong

25000
20000
15000
10000
5000
0

Fig. 2: The variety of phytoplankton density of each waterbody group
b. Zooplankton
There were 10 taxa of zooplankton identified including three groups; the most abundant
was copepod, and the last is Balanus amphitrite that is only appearing in the salinity effected
areas.
The distributions of zooplankton were not same in each group of pond, the details were
displayed on the table 5. The same way that showed is the taxa number of copepod but their
ration were not same because of the difference of diversity of each water bodies. The number of
species of weakness group is less than in the strong one; it could be the high gradient of
environmental factors is not suitable for the shrimp stand.
Table 5: The variety of taxa of zooplankton in each group of shrimp pond
Canal

Weakness ponds

Strong ponds

Number
of Taxa

Ratio
%

Number
of Taxa

Ratio
%

Number
of Taxa

Ratio
%

Copepod

2

28.57

2

33.33

2

28.57

Rotifera

4

57.14

3

50.00

4

57.14

Other

1

14.28

1

16.67

1

14.28

Total

7

6

7
10


Copepod is the abundant group, most of them belong to the suborder of Cyclopoida that
is the organivorous. So it could say that these areas are a little bit of pollution of organic matter.
On the other hand, the species Enterfer acutifonts is also found in the plankton samples, It is the
indicator for the low water level of the shrimp ponds. Acartia pacifica is the high tolerance
species, It is the indicator for the high variety of environmental factors.
Rotifera is abundant in the hamlet of Chuchot and 19. It could tell that the organic
matters were high.
The densities of zooplankton were about 400 – 118400 ct/m3 . Each dominant groups of
zooplankton could explain the water quality, how is suitable for shrimp living. Copepod is
always dominant in the pond that often exchanges water, but the total density was not high.
Rotifera were dominant in the pond that is high organic matter, total density is too high because
of the rapid recruitment of rotifera. On the other hand, when the disease were found, the farmers
try to rescue by using chemical, that could effect to zooplankton. So the simple structure of
zooplankton component showed the pollution of environment. The gradients of zooplankton of
?the strong shrimp pond group were too high (std >200%)?because of the variety of dominant
group of zooplankton. If each group of zooplankton could not dominate, they did not get the high
density then the gradient of zooplankton was not high.

Density (ind./m3)

100000
80000

Weakness
Canal

60000

Strong

40000
20000
0

Fig. 3: Variety of zooplankton density of each shrimp pond group
4. The reason of the disease breakout
Generally, the main reason to cause the death of shrimp in the pond was the disease
break out from the infected shrimp larva that were stocked to shrimp pond. But that could not
break out to the whole coastal area of Mekongdelta. Other reasons will be discussed in the next
session.
a. The knowledge of farmers on shrimp culture
After interviewing both successful and fail farmers, the mistake could be:
- Recruimented stocking: All of the interviewed farmer stock shrimp twice per month.
According to their opinion, every month they harvest so they need to recruit them. If they
11

stocking one time they have to wait next 3 or 4 month for harvest, so they did not get income on
the free time. They did not understand that the larger shrimp could use the smaller shrimp as
natural food, unintentional the farmer supplemented the very expensive food for their first
stocking shrimp. Addition, if the last stock shrimps were not the feed, total densities of shrimp is
about 10 - 15 ind./m2 . That is not the improved extensive system because the shrimp density is
more than 2 ind./m2 . The risk is always around their shrimp pond if they are poor the knowledge.
- The limiting of improve the pond: The shrimp farmers said that the improvement of the
pond can kill the natural shr imp such as Metapenaeus spp, then they did not get income from the
harvesting everyday. Because of poor, they thought that but they did not understand that the seed
of disease can live in the bottom of the pond, they are easy make diseases if the stocking shrimp
are not strong enough. It is necessary to teach them how to improve the pond and explain them
what is the main income and how to get success from there.
- Cutting out of the grass or forest to increase the water surface: To increase the areas of
water for shrimp culture, the farmers try to cut down all of the tree on the ponds. They did not
know that cutting off plant is useful for the intensive culture, water level is about 1.0 m for the
whole pond but on the extensive system, the shadow is necessary for the large area with low
level water. 20% of the extensive pond is covered by 1.0 m of water, the remain is less than 0.4m
of water depth so that can not control the temperature of water when the sun shine and at night,
temperature releases fast by the large areas. The gradient of temperature is high is not suitable
for shrimp culture. To resolve this problem, It is necessary to cultivate the grass or forest on the
large areas to reduce the gradient of temperature, on the other hand, natural food will be
improved by the development of insect. Alternative rice in the rainy season and shrimp in the
drying season could be suitable.
-Misunderstanding about the role of environment factors: The farmers did not understand
the meaning of each environmental parameters then they did not how to control the water
quality, particularly some of them did not how to test pH of the pond. They stock shrimp larvae
for their season depend on the season of the local zone, and looking the water of canal to get in
the pond if it is not dirty. The aquaculture extension centers have to improve the knowledge of
the farmers to reduce the risk when they start their cultivation.
- Not clearly understanding about the fertilizer or treatment chemicals: low education is

the limit of the farmer about the chemical for shrimp treatment. The uncontrolled promotion of
the chemical using on the shrimp pond could be harmful because the farmer did not know what
is the disease and what is the medicine. Furthermore the farmers can not control themselves
when the problems happen on their pond and then they can not control the disease.
b. The popular current methods of shrimp cultivation
To resolve the problems happened when the disease break out, it is necessary to know
what is the standard and how can help the farmer apply correctly. Now, there are some methods
were used for shrimp culture in Vietnam, they were explained below.
- Improved extensive system: The shrimp could be integrated cultured with forest or
paddy field or alternative rice-shrimp. The density of stocking shrimp is about 2 ind./m2 with the
12


size of 2-3 cm (that called earthen pond seed). It is necessary to control the trace fish and
predators by drying the pond and liming. Feeding is not need, exchanging water when
harvesting. Harvesting is done every half of lunar month. The trees on the pond are kept to
control the water temperature.
- Semi-intensive system : This is the high techniques of shrimp culture, the pond would be
managed better, area is about 1000-3000m2 , water depth is about 1 – 1.2m, shrimp density is
about 5-7 ind./m2 , feeding was scheduler everyday with the ratio belongs to age of shrimp,
normally, it is about 10% of shrimp weight, the protein is about 20-30% weight of feed. The
pond need to improve well, the environment parameters should be test frequently. Water should
be exchanged actively. It is necessary to have two canals, one is used for flowing in and another
is used for flowing out to reduce the spread of disease.
- Intensive system: this is the highest ranker technique of shrimp culture that is suitable
for the high level education and high fund farmer. The pond should be improved carefully, the
environmental parameters are test twice per day, aeration is needed. Artificial fillet should be
supplied with the weight that follows the manual, shrimp density is more than 40 ind./m2 . Water
should be exchanged actively. It is necessary to have two canals, one is used for flowing in and
another is used for flowing out, water should be treat before supplying shrimp pond

c. Planing for sustanable of shrimp cultivation
After interviewing and assessment the results, it could say that the risk was improved
from the knowledge of farmer about the technique of shrimp culture. To reduce the problems, it
is needed to follow some ideals:
- It is needed to improve the plant systems on the pond, apply correct the guideline from
the semi-extensive shrimp culture manual. After doing the suggestion, the gradient of the
environment factors is not high, shrimp could not get the stress.
- If it can be used for semi- intensive culture, It is necessary to divide the total areas of
shrimp culture into three parts: (i) the first area that is near the water supply should be used for
improve extensive culture, The farmer could harvest every high tide to get income for daily
living, (ii) the middle part could be used for reservoir and treatment and (iii) the last one with the
lowest area, could be used for semi intensive culture. In the first time, the middle part should be
used the lowest, gradually, the farmers understand the important role of reservoir, and they will
accept the new technique.
- Restoring the areas that could be used for integrated rice and shrimp cultivation.
- In the salinity intrusion areas, the farmer should accept the plan from the local
government to reduce the risk and the pollution. If the farmer carried out their plan by
themselves, it could be out of plan, the infrastructure such as canal, salinity and etc... could not
be good for them then the disease gets the opportunity for break out.

13


IV. CONCLUSION
Some problems of environment of shrimp pond could be found on the results of
analyzing, these effects would be solve or reduce if the farmer accept the scientific advises. The
disease break out because of the high gradient of environmental factors, they are:
- The gradient of temperature is too high for shrimp to stand. These shrimps get stress,
and weak to be easy infected.
- The preparation of the ponds are not good enough, using the recycled brackish water

could make the pollution in the pond. The shrimp can not be well on that bad environment, then
the disease could break out.
- The water supply or territorial canal systems were not good enough to flow in and out
then the disease could be easy to expand in the whole area.
- The knowledge of farmers about the shrimp culture is poor, they did not understand
well about the shrimp farming chemicals.
RECOMMENDATION
- Strengthening the activity of aquaculture extension, supporting the shrimp culture
techniques to farmers. Being able develop the demonstration farms at the local areas to teach the
farmers how to culture shrimp well.
- Planning and building the water supply systems at the areas that is master planned for
shrimp culturing.
- Decreasing the self doing of the farmers, it is necessary to make the cooperative or club
for the shrimp farmer to help together when they get any problem.
- Being careful when using the chemicals
REFERENCE
1. Akihiko Shirota. 1966. Plankton of south Vietnam. Faculty of Science, Saigon university and
Oceanography Institute of Nhatrang. Overseas technical corporation Agency. Japan.
2. Edmondson. W.T. 1959. Freshwater Biology (second edition). University of Washinton,
Seattle
3. Robert W. Pennak. 1978. Fresh-water invertebrates of the United states. A wiley-interscience
publication.
4. Dang Ngoc Thanh, Thai Tran Bai, Pham Van Mien. 1980. Identification the fresh water
invertebrates of North of Vietnam. Science and Technology publish house of Hanoi.
5. Vu Trung Tang. 1994. The estuaring ecosystem of Vietnam. Science and Technology publish
house of Hanoi.
14


APPENDIX

ANNEX 1. PHYSICAL AND CHEMICAL WATER QUALITY
Temp.
(o C)
27.8

pH

Salinity
o
/oo

Turb.
NTU

H2 S
ppm

Fe
ppm

COD
ppm

DO
ppm

NH4 +
ppm

PO43ppm

NO3 ppm

6.2

30

18

0.96

8.34

512

3.32

0.74

0.172

1.077

Hamlet 23–weakness

31.9

7.98

29.9

40.9

1.12

9.22

608

3.36

0.66

0.017

0.554

Hamlet 23-strong

30.2

7.76

24.3

45

0.88

17.88

288

2.57

0.54

0.019

0.794

Hamlet 23–weakness

31.6

8.84

21.3

46.6

0.96

15.46

320

2.39

0.56

0.013

0.723

Hamlet 19 – strong

30.1

7.5

26.9

6.9

1.12

5.23

288

2.56

0.58

0.147

0.976

Hamlet 19 – strong

29.0

8.02

21.8

34.9

1.28

12.09

272

3.53

2.12

0.085

0.596

Hamlet 19–weakness

28.5

7.6

22.9

55.6

1.52

18.13

288

2.23

0.26

0.234

0.216

Phuocthohau-weak

33.0

8.64

20.9

49

1.28

23.5

416

4.60

0.24

0.019

0.672

Phuocthohau-strong

31.9

7.45

26.4

17.7

1.28

7.37

432

5.20

1.28

0.011

0.727

Phuocthohau-strong

31.2

8.48

27.1

24.1

1.76

7.77

520

5.00

0.32

0.022

0.744

Phuocthohau-weak

30.4

7.88

21.6

27.9

1.44

11.24

424

3.70

1.48

0.038

0.934

Chuchot - weakness

32.0

9.52

23.9

34.2

1.52

8.64

576

5.70

1.00

0.018

0.625

Chuchot - weakness

31.4

9.36

26.3

40.5

1.60

7.99

448

4.60

1.46

0.016

0.706

Chuchot - strong

31.5

6.31

25.9

19.5

1.60

9.85

272

4.90

0.70

0.011

0.511

Ponds of
Daidien–weakness

15


ANNEX 2: PHYTOPLANKTON
1. Taxa
No Taxa

Daidien
C

S

Hamlet 19
W

C

S

Hamlet 23

W

C

S

Phuocthohau

W

C

S

W

Chuchot
C

S

W

Bacillariophyta
1 Amphipleura pellucida

+

2 Amphipleura alata

+

3 Amphiprora gigantea

+

4 Campylodiscus daemelianus

+

5 Campylodiscus echeneis

+

+

6 Campylodiscus ornatus

+

7 Coscinodiscus lineatus

+

8 Coscinodiscus marginatus

+

9 Coscinodiscus nodulifer

+

+

10 Cyclotella meneghiniana

+

11 Fragillaria intermedia

+

+

12 Gymnodinium neglectum
13 Gyrosigma acuminatum

16 Nitzschia filiformis

+

+
+

+

+

+

+
+

14 Gyrosigma attenuatum
15 Nitzschia closterium

+

+
+

+

+
+
16


17 Nitzschia longisigma var reversa

+

+

+

18 Nitzschia philippinarum

+

19 Nitzschia seriata
20 Nitzschia sigma var interdens

+
+

+

21 Nitzschia vermicularis

+

+
+

+

+

+
+

+

22 Synedra ulna

+

Cyanophyta
23 Lyngbya birgei

+

24 Microcystis aeruginosa
25 Oscillatoria formosana

+
+

+

+

26 Oscillatoria princeps

+

27 Phormidium autumpale

+

28 Trichodesmium erytheraeum

+

+
+

+
+

+

+

+

Chlorophyta
29 Mougeotia viridis
30 Spyrogyra azygospera

+
+

31 Spyrogyra ionia

+

+

+

Pyrrophyta
32 Goniaulax palutre
33 Peridinium spriferum

+
+

Note: C: canal, S: strong shrimp pond; w: weakness shrimp pond
17

2. Density (cell/ml)
No

Status

Hamlet

Bacillariophyta
Density

Ratio

Cyanophyta
Density

Ratio

Chlorophyta
Density

Ratio

Pyrrophyta
Density

T?ng

Ratio

1 W

19-Phongthanh

400

100.00

0.00

400

2 W

23-Phongthanh

2000

100.00

0.00

2000

3 W

Chuchot

800

33.33

400

16.67

4 W

Phuocthohau

800

28.57

2000

71.43

5 C

Chuchot

16800

42.42

400

1.01

6 C

Phuocthohauu

1600

100.00

7 C

19-Phongthanh

2800

77.78

8 C

23-Phongthanh

3200

9 C

Daidien

10 S

1200

50.00

2400
2800

22400

56.57

39600

0.00

1600

800

22.22

3600

80.00

800

20.00

4000

8800

50.00

8800

50.00

17600

19-Phongthanh

2000

83.33

400

16.67

2400

11 S

23-Phongthanh

800

7.14

2000

17.86

12 S

Daidien

800

50.00

800

50.00

13 S

Chuchot

1600

66.67

400

16.67

14 S

Phuocthohauu

1600

80.00

400

20.00

8400

75.00

11200
1600
400

16.67

2400
2000

Note: C: canal, S: strong shrimp pond; w: weakness shrimp pond

18