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

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

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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.

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

  1. 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
  2. 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
  3. 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) College of Agiculture – Cantho University (2) College of Technology – Cantho university 2
  4. 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
  5. 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
  6. 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.1600a. 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 + Calculating density of zooplankton by using the function: d = 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). 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
  7. 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 Convert from EC Turbidity (NTU) 18 – 55 6.9 – 45 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
  8. 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. 40.0 Strong shrimp pond Weakness shrimp pond Temperature (oC) Strong shrimp pond 30.0 30.0 Weakness shrimp pond 20.0 25.0 Salinity (ppt) 20.0 10.0 15.0 0.0 10.0 5.0 0.0 Strong shrimp pond Strong shrimp pond 10.0 Weakness shrimp pond 50.0 Weakness shrimp pond 8.0 40.0 Turbidity (NTU) 6.0 pH 30.0 4.0 20.0 2.0 10.0 0.0 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
  9. 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
  10. 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 NO3- 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. f. PO43- The concentration of this factor is stable by the absorbing of the mud so it is about 0.01- 0.23 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
  11. 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 Ratio Number Ratio Number Ratio of species % of species % of species % 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
  12. 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. 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 Density (cell/mL) 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 Ratio Number Ratio Number Ratio of Taxa % of Taxa % of Taxa % 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
  13. 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. 100000 80000 Weakness Density (ind./m3) 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
  14. 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
  15. 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
  16. 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
  17. APPENDIX ANNEX 1. PHYSICAL AND CHEMICAL WATER QUALITY Ponds of Temp. pH Salinity Turb. H2 S Fe COD DO NH4 + PO43- NO3 - (o C) o /oo NTU ppm ppm ppm ppm ppm ppm ppm Daidien–weakness 27.8 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 15
  18. ANNEX 2: PHYTOPLANKTON 1. Taxa No Taxa Daidien Hamlet 19 Hamlet 23 Phuocthohau Chuchot C S W C S W C S W C S W 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 + + + + 14 Gyrosigma attenuatum + 15 Nitzschia closterium + + 16 Nitzschia filiformis + 16
  19. 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
  20. 2. Density (cell/ml) No Status Hamlet Bacillariophyta Cyanophyta Chlorophyta Pyrrophyta T?ng Density Ratio Density Ratio Density Ratio Density 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 1200 50.00 2400 4 W Phuocthohau 800 28.57 2000 71.43 2800 5 C Chuchot 16800 42.42 400 1.01 22400 56.57 39600 6 C Phuocthohauu 1600 100.00 0.00 1600 7 C 19-Phongthanh 2800 77.78 800 22.22 3600 8 C 23-Phongthanh 3200 80.00 800 20.00 4000 9 C Daidien 8800 50.00 8800 50.00 17600 10 S 19-Phongthanh 2000 83.33 400 16.67 2400 11 S 23-Phongthanh 800 7.14 2000 17.86 8400 75.00 11200 12 S Daidien 800 50.00 800 50.00 1600 13 S Chuchot 1600 66.67 400 16.67 400 16.67 2400 14 S Phuocthohauu 1600 80.00 400 20.00 2000 Note: C: canal, S: strong shrimp pond; w: weakness shrimp pond 18

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