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

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.. in the s

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

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 H2S 7

c Total iron 7

d Concentration of NH 4+ 7

e Concentration of NO 3- 8

f PO 43- 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

Environmental Rapid Assessment the break-out shrimp diseases

of Baclieu province, Mekong delta, Vietnam

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

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 32oC - 33oC, nighttime 22oC - 23oC) 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

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)

- 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 4oC 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, H2S, NH4+, NO3-, P-PO43- and COD

b Plankton

- Using plankton nets with the mesh size are a = 25 µ and59 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

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

- H2S, Fe, COD, NH4+, PO43-, NO3-: 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 number with the function

v c

a x

d

5.16

.1600

= where d: density of phytoplankton (cell/ml); x : number

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)

+ Calculating density of zooplankton by using the function: 1000

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

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

2oC, 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

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

0.0 10.0 20.0 30.0 40.0 50.0

Strong shrimp pond Weakness shrimp pond

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, H2S, 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)

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

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

H2S, 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

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

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

The 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

The concentration of this factor is stable by the absorbing of the mud so it is about 0.23 ppm and 0.01-0.15 ppm in the both groups (weakness and strong shrimp ponds, respectively)

0.01-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