WATER QUALITY MONITORING IN STRIPED CATFISH (Pangasianodon hypophthalmus) FARMS IN THE MEKONG RIVER DELTA, VIETNAM
Nguyen T. Phuong, Vu N. Ut, Vuong T. Tung, Nguyen T.T. Hang, Nguyen T.K. Lien, Duong T.H. Oanh, Dang T.H. Oanh and Do T.T. Huong
College of Aquaculture and Fisheires, Can Tho University, Viet Nam
Ernesto J. Morales Sustainable Fisheries Partnership
Abstract Water quality in striped catfish (Pangasianodon hypophthalmus) production systems in the Mekong Delta was investigated to assess the potential impacts of the culture activity on the environment. The study was conducted at three culture systems, so called systems 1, 2 and 3 selected from catfish culture areas of An Giang, Can Tho, Dong Thap and Hau Giang provinces. These systems were categorized based on their location to water sources and separation of inlets and outlets. Systems 1 and 2 were closed to big rivers, but most of the farms in system 1 were not connected directly to the rivers (using pumping); whereas, most of farms in system 3 were only located near to small rivers. Among the three systems, only system 1 was constructed with separate outlets and inlets, whilst in system 2 and 3 inlets and outlets were designed at the same side of the farms. A total of 21 sites were selected from 10 farms of these three systems for sampling. In system 1, sampling was implemented at inlets, culture ponds and outlets, whereas in system 2 and 3 samples were only obtained from inlets and culture ponds. Sampling was conducted throughout two production cycles with three periods including beginning, middle and the end of each cycle. Sampling program was implemented with 3 major groups of samples including water quality (chemical and physical water parameters and plankton), residues of antibiotics and organic compounds, and microbial samples (bacteria, parasites and coli forms). Main water parameters taken for the assessment consisted of temperature, pH, DO, BOD, COD, - - turbidity, total alkalinity, total hardness, TAN, N-NO2 , N-NO3 , TSS, TN and TP. Phytoplankton and zooplankton were also simultaneously collected. Chemical and physical water parameters were sampled and analysed by applying fundamental methods used at the laboratory of College of Aquaculture and Fisheries, Cantho University. Phytoplankton and zooplankton were qualitatively and quantitatively collected by plankton nets of 27 !m and 60 !m, respectively, except quantitative samples of phytoplankton were obtained with settling method. Total count of bacteria from water sample was determined using 10-fold dilutions method. Hearvy metals; and pesticides and antibiotic residues were analyzed using AAS (Atomic Absorption Spectroscopy), GC MS/MS (Gas Chromatography tandem Mass Spectrometry) and LC MS/MS (Liquid Chromatography tandem Mass Spectrometry) based methods, respectively. The results indicated that most of parameters were still in the acceptable ranges except TN and TP. Dissolved oxygen concentrations in all systems were constantly above 4 mg/L for both crops. BOD and COD were averagely low although high values were measured in some period. The highest concentrations of BOD and COD recorded only in crop 1 were 10.7 mg/L and 19.6 mg/L in system 1 and system 3, respectively. Mean concentrations of TSS were relatively low in all systems of both crops ranging from 21 to 87 mg/L. However, TN and TP concentrations were considerably high. Concentrations of TP recorded outside the culture ponds were 3 and 10 times higher than the standard levels (0.1 mg/L). TP
1 concentrations tended to increase steadily throughout the production period. However, mean TN concentrations were acceptable followed the recommended level (10 mg/L) but in some sites at certain periods it reached very high levels (up to 28.8 and 35.9 mg/L in culture ponds in crop 1 and 2, respectively). There were about 48% and 30% of culture ponds in crop 1 and crop 2 having TN exceeding the recommended level, whereas almost 100% of sites having TP concentration exceeding recommended level. Significantly high concentrations of TN and TP recorded both outside and inside of the production systems have indicated that eutrophication would be inevitable. Measures including waste treatment methods, planning policies, etc… should be taken into consideration to ensure the sustainability of culture industry. The results also indicated that development of algae and zooplankton in catfish production system involved species that are preferable to nutrient rich environment. Species of algae recorded belong to five phyla with 257 genera, in which green algae were the dominated group. Zooplankton also presented with eutrophic preferable groups such as rotifers, protozoa. At all sites of 3 systems for both crops, increase in species number and densities of algae at the end of crop indicated that water quality in the catfish production system decreased toward the end of production cycle. Total bacterial counts at all sampling spots were in acceptable ranges for aquaculture environment. Total coliform counts were acceptable in most of analyzed samples accept 14 samples that coliform counts !200 CFU/g. The levels of pesticides in water sources for striped catfish farming has no or very low. Among five main haevy metals including Cupper (Cu), Arsenic (As), Cadmium (Cd), lead (Pb) and mercury (Hg), the Cu was detected in all samples (crop-1 and crop-2) and Pb was also found in all samples of crop-1 and 65% samples of crop-1. Cd and As were found at low percentage in samples of crop-1 and crop-2. In contrast, Hg was not found in any collected sanples. The concentration of antibiotic residues detected from samples varied greatly. There were only four samples of crop-1 containing encrofloxacine of 1,863 ppb and norfloxacine 740; 743 and 1,501 bbp, which were extemely high, while other samples were free of antibiotic residues.
2 1 BACKGROUND The Mekong delta in the Southern part of Vietnam is known as the region for catfish farming. Catfishes in Viet Nam comprise two genera, Pangasius (10 species) and Pangasianodon (1 species). These species also occur in Cambodia, Laos and Thailand (www.fishbase.org). Of these, Pangasianodon hypophthalmus have been farmed in the Mekong delta for decades. The striped catfish has been traditionally farmed in latrine ponds using wild seed for few decades and become commercial culture in cages, pens and ponds after the artificial mass seed production commencing in 2000 (Tuan et al., 2003). Recently, the striped catfish plays a very important and significant role in the aquaculture sector of Viet Nam. Its production was approximately 1,200,000 t accounting for more than 50% of the total aquaculture production of Viet Nam in 2007 (Figure 1). The growth of striped catfish farming has been dramatically increased in ten years from 1997 to 2007. Farming areas increased about 8-fold from 1,250 ha to over 6,000 ha, while the production increased 45-fold from around 22,500 t to 1,200,000 t (Dung, 2008). As this trend, striped catfish will continue to be the key targeted culture species of Vietnamese aquaculture and will have a strong impact on the success of the whole aquaculture sector of the country. Striped catfish culture is based on the advantage of plentiful water supply from Mekong River. The environmental management of striped culture models is largely depended on river water. High rate of water exchange is the main method applied to improve pond water quality. The sustainability of striped catfish farming is very well related to external water environment. High amount of effluents from striped catfish ponds are impractical to treat have been considered as a source of pollutant causing degradation of water environment. Although, catfish farms are mostly located along two branches of Mekong River which can help to sweep away waste matters to minimize pollution, but localized pollution of water environment has been recorded in concentrated farms. Control of water quality from striped catfish pond culture system to minimize environmental pollution is crucial issue to enable the sustainable development of striped catfish culture in the delta. Diseases in striped catfish farming has been one of serious obstacles to the sustainable development. Several pathogens have been reported to be associated with diseases in striped catfish culture include fungus, ento- and ecto-parasites as well as bacteria. Among the infectious diseases, bacterial agents have been responsible for the major epizootics affecting the striped catfish farming. White spots on the internal organs caused by Edwardsiella ictaluri and hemorrhagic symptoms caused by pathogenic Aeromonas hydrophilla,… have been reported as the most serious diseases Phuong et al., 2007). The use of chemicals and drugs is very common in catfish farming and relates to the food safety. Liem (2008) found that there are 39 kind of chemicals and drugs used for water quality regulation and disease treatment and prevention. In fact, the list of banned or limited use antibiotics and chemicals use in aquaculture in Viet Nam has been updated regularly. Recently, only few antibiotics are allowed to use in catfish farming. This study is aimed to better understanding the productin trend and the environmental impacts of striped catfish farming in the Mekong Delta. The collected information are also important for the development of water quality and food safety standards.
3 2,250 Catfish 2,000 Total aquaculture 1,750
1,500
1,250
1,000
Production (x1,000 t) (x1,000 Production 750
500
250
- 1999 2000 2001 2002 2003 2004 2005 2006 2007
Figure 1: Production of striped catfish in comparison with total aquaculture production in Viet Nam (Complied from Phuong, 2007 and Dung, 2008)
2 RESEARCH METHODOLOGIES 2.1 Site selection Based on a series of field visits and secondary information, three types of striped catfish farming systems were identified including: " System-1: large scale farms with plenty of ponds, separate inlets and outlets, located near big rivers but not directly connected to the rivers. Water samples were taken at the supply canal, culture pond and discharged canal. " System-2: large scale farms but without separate inlets and outlets, also located near big rivers but connected directly to the rivers. Samples were taken at supply canal and culture pond. " System-3: medium and small scale farms without discharged canal, mostly located near small rivers. Samples were taken at the supply canal and culture pond. Farm sites were selected in the most important striped catfish culture areas in the Mekong Delta. The first sampling (crop 1) was in Phung Hiep district, Hau Giang province (3 farms with 7 sampling sites), Thot Not district, Can Tho city (4 farms with 9 sampling sites) and Chau Phu district, An Giang province (2 farms with 5 sampling sites) (Fig. 1). Farm sites of crop 2 were in Phung Hiep districts, Hau Giang province (2 farms), Thot Not district, Can Tho city (2 farms), Binh Tan district, Vinh Long province (3 farms) and Sa Dec district, Dong Thap province (2 farms)
4
: Sampling site Figure 2: General layout of studied systems of crop 1 with locations and sites selected for sampling at 9 striped catfish farms in Thot Not district (Can Tho City), Chau Phu (An Giang province) and Phugn Hiep (Hau Giang province). Round spots represent for sampling sites (21 sites).
2.2 Sampling procedure The study were conducted for two production cycles, each production cycle was about 6 months. The first study or sampling started from January, 2008 and ended in August, 2008. The second sampling was commenced in December, 2008 and completed in May, 2009. Three sampling periods were implemented including (i) at the beginning of crop (fish at around 100-200g), (ii) at the middle of crop (fish at 400–500 g) and (iii) at the end of crop (before harvest – fish reach marketable size of 1,000 g). At each sampling sites/farm, a short baseline survey was also conducted in order to understand the management practices and to determine its effect (feeding) to the water quality. 2.3 Analytical methods 2.3.1 Water quality parameters All physical and chemical water parameters were analyzed at the water chemistry laboratory of the College of Aquaculture and Fisheries, Can Tho University. The water sampling and analysis were followed the methods described in Table 1.
5 Table 1: Water parameters collected in the monitoring study Parameters Sampling methods Analytical Technique Temperature On-site Thermometer (YSI) pH On-site pH meter (YSI) Total alkalinity Water was filled in 2 L plastic Titration with acid Total hardness bottle and kept in cool box at Titration with EDTA temperature of <40C DO On-site DO meter (YSI) BOD Water was filled in 2 L plastic Respirometric bottle and kept in cool box at temperature of <40C
COD Water was filled in 125ml Oxidized with KMnO4 in white glass bottle and alkaline medium conserved with 2ml H2SO4 Total ammonia Indo-phenol blue Nitrogen (TAN) Total nitrogen (TN) Kejdalh and Indo-phenol blue Reactive phosphorus Ascorbic acid -3 Water was filled in 2 L plastic (PO4 ) bottle and kept in cool box at Total phosphorus (TP) Kejdalh and acid Ascorbic temperature of <40C Turbidity Nephelometric Total suspended Filtering and drying at 103- Solids (TSS) 1050C Settleable solids Using imhoff cone
Quantitative and qualitative samples of phytoplankton, zooplankton and benthos were also collected. Phytoplankton and zooplankton were sampled with fine plankton net of 27 !m and of 60 !m mesh size, respectively. Both qualitative and quantitative samples were taken from 5 points in the ponds or rivers/canals. Quantitatively, phytoplankton samples were pooled in a bucket and a composite sample was taken in a 1 L plastic bottle for further analysis, while zooplankton samples were filtered through the net with determined volume. The samples were fixed with 4% and analyzed at the Hydrobiology lab in the College of Aquaculture and Fisheries, Cantho University.
2.3.2 Heavy metals, pesticides and antibiotics The heavy metals, pesticides and antibiotics were sampled and analyzed using method described in the table 2.
6 Table 2: List of contaminants tested during the water monitoring study Parameters Sampling methods Analytical methods Heavy metals Cadmium (Cd) AAS Arsenic (As) Water was filled in 2 L AAS Mercury (Hg) plastic bottle and kept in cool AAS 0 Lead (Pb) box at temperature of <4 C AAS Copper (Cu) AAS Pesticides Organophosphorus pesticides Water was filled in 2 L GC MS/MS Chlorinated pesticides plastic bottle and kept in cool GC MS/MS box at temperature of <40C Antibiotics Chloramphenicol (CAP) LC MS/MS Enrofloxacin LC MS/MS Norfloxacine Fish muscle was collected LC MS/MS and stored at temperature of - Ciprofloxacin 40 0C LC MS/MS Malachite green (MG and LMG) LC MS/MS Nitrofurans (AMOZ) LC MS/MS Note: AAS: Atomic Absorption Spectroscopy; GC MS/MS: Gas Chromatography tandem Mass Spectrometry; LC MS/MS: Liquid Chromatography tandem Mass Spectrometry The limits of detection (LOD) for antibiotics, heavy metals and pesticides are presented in table 3.
Table 3: The limits of detection (LOD) for antibiotics, heavy metals and pesticides No. Parameters Antibiotics Heavy metals Pesticides (ppb) (ppb) (ppb) Antibiotics 1. Chloramphenicol (CAP) 0.1 2. Enrofloxacin 2 3. Ciprofloxacin 2 4. Norfloxacine 1 5. Malachite green (MG) 1 6. LMG 1 7. Nitrofurans (AMOZ) 1 Heavy metals 1. Cupper (Cu) 0.5 2. Arsenic (As) 1 3. Cadmium (Cd) 0.1 4. Lead (Pb) 1 5. Mercury (Hg) 0.25 Pesticides Organophosphorus pesticides 1. Triethylphospo 20
7 2. Thionazin 50 3. Sulfotep 50 4. Phorate 50 5. Dimethoate 80 6. Disulfoton 50 7. Methyl parathion 50 8. Parathion 80 9. Farmphur 80 Organochlorine pesticides 10. Aldrin 10 11. Endrin 80 12. Diendrin 20 13. Endrin aldehyte 50 14. Endrin ketone 80 15. Methocychlor 80 16. Heptachlor 50 17. Heptachlor epoxide 50 18. #-BHC 50 19. $-BHC 50 20. Delta-BHC 50 21. Gamma-BHC 50 22. 4,4 DDD 80 23. 4,4DDE 10 24. 4,4 DDT 20 25. #-endosulfan-I 10 26. $-endosulfan-II 50 27. Endosulfan sulfate 80
2.3.3 Total bacteria and coliform a) Determination of total bacteria Total count of bacteria from water sample was determined using 10-fold dilutions method. Brieftly, 1 mL of water sample was added to a tube containing 9 mL sterile saline. Continue with this dilution to prepare a series of 10-fold dilutions up to 10E-3. Make sure that all dilutions are well homogenized. 100 uL of each dilution was spot in Trypton Soya Agar (TSA) plates a. Spread plate the suspension using a sterile glass triangle rod. Allow the plates to dry for max. 10 minutes and incubate at 28 ºC overnight. The number of bacteria in each dilution was calculated using the following formula: CFU/ml = number of colonies x dilution fold x 10 Total count of bacteria in the sample was an average of bacteria number (CFU/ml) from there dilutions. b) Determination of coliform Ten grams muscle of each fish sample was cut by sterile tool. Sample was then put into bag mixer and pulverized before mixing with 90ml of sterilized peptone water. Continue with this dilution to prepare a dilutions 10E-3. 1ml diluted sample was
8 transferred into 2 sterile plates and pour off 15 ml VRLB medium (containing 1% lactose at 45oC). The sample was mixed with VRLB medium and allow it to be complete solid before adding extra 4 ml 4 ml VRLB on the surface. The plate was then incubate for 24h at 37 ºC. Number of coliform in each fish sample was calculated by the formula:
X = "C/(n1+0.1 n2) d In which: "C: Total specific colony counted in all plates n1: The plates was kept for the first dilution n2: The plates was kept for the second dilution d: dilute coefficient correlative to the first dilution
9 3 RESULTS AND DISCUSSION
3.1 Water quality
3.1.1 Crop-1
3.1.1.1 Water physical and chemical characteristics
a) River (inlet) water Temperature ranged from 27.1oC to 31.9oC, with the average of 29.5oC. This range of temperature is typical and suitable for tropical aquatic organisms. There were only 2 sites (8%) having temperature slightly greater than 32oC. pH was also in the suitable range (6.8-8.2) with a mean value of 7.3. The most common range of pH recorded was from 6.93 to 7.59 accounting for 72% of total sampling sites. Dissolved oxygen concentrations were ranging from about 4 to 10.7 mg/L. This range is very ideal for aquatic organisms and additionally indicating low levels of organic matter. More than 70% of sites contained DO concentrations of about 5 to 9 mg/L. BOD and COD concentrations were low ranging within the limits of the national standard (TCVN 5942-1995). The values of BOD and COD levels presented in Table 1 indicated that organic matter contents existing in the water sources may not be problematic. Most studied sites (70%), BOD ranged from 0.2 to 5 mgO2/L. Similarly, common COD concentrations varied in a range of 0.4-7.2 mgO2/L.
Table 4: Water parameters recorded in the inlets (rivers) of the catfish production systems presented with values of mean, max and min of all 9 selected catfish ponds of crop 1. Parameters Mean Std Max Min Temperature (oC) 29.5 1.26 31.9 27.1 pH 7.28 0.46 8.75 6.79 DO (mg/L) 7.42 1.69 10.7 3.92
BOD (mgO2/L) 3.54 3.02 8.56 0.24
COD (mgO2/L) 6.74 4.92 19.2 0.40 Turbidity (NTU) 35.8 28.1 120 8.00
Alkalinity (mg CaCO3/L) 59.8 7.85 76.0 45.0 Hardness (mg/L) 37.4 9.82 56.5 20.5 TAN (mg/L) 0.27 0.34 1.50 0.03 NO2- (mg/L) 0.09 0.20 1.04 0.00 NO3- (mg/L) 1.14 0.89 3.89 0.05 PO43- (mg/L) 0.20 0.25 1.04 0.01 TSS (mg/L) 47.3 27.9 113.5 15.2 TN (mg/L) 5.63 4.66 18.84 0.34 TP (mg/L) 1.23 1.05 4.65 0.02
- - Total ammonia (TAN), nitrite (NO2 ) and nitrate (NO3 ) concentrations were all low. The maximum concentration of TAN that found only in one site was 1.50 mg/L. About 96% of sites had suitably low nitrite concentration (0.01-0.13 mg/L). Nitrate was also very low. The most commonly recorded concentrations were from 0.4-1.8 mg/L. Although 3- phosphate (PO4 ) concentrations were rather high in some areas of the rivers compared to the recommended levels (Boyd, 1998), the mean concentrations were still acceptable (0.2 mg/L compared to 0.1 mg/L, respectively). Nearly 70% of the sites contained a suitable 3- range of PO4 (0.01-0.13 mg/L). Total nitrogen (TN) and total phosphorus (TP) 10 concentrations were much higher than levels recommended by Boyd (1998) that TN and TP should not exceed 3 mg/L and 0.1 mg/L, respectively to prevent from eutrophication. There was up to 72% of sites having TN concentrations greater than 3 mg/L (varying from 3.32-18.84 mg/L). The most common range of TN in this system was 3.42-6.5 mg/L. Similarly, TP concentrations of greater than 0.1 mg/L existed in 92% of sites (0.13-4.65 mg/L). The most common range varied from 0.9 -1.8 mg/L. Mean, maximum and minimum values of measured parameters in the rivers are presented in Table 4 and the details are in Appendix 1.
b) Culture pond water Similar to the results recorded from rivers, most of parameters measured in the ponds were in acceptable ranges, though they were more variable than those in the rivers (Table 5). Temperature was completely lying in the suitable range for growth of catfish, ranging from 27.9 to 32.0 oC. pH values seemed to be more variable than those in the rivers perhaps due to fluctuation of phytoplankton and culture practices (e.g. liming, exchanging water,…). Commonly, pH in the culture ponds concentrated around the mean value of 7.14 (ranging from 6.8-8.1). DO concentrations were suitably high (averaging 6.20 mg/L). There were only two particular cases of low DO levels recorded in one pond in Chau Phu, An Giang (2.28 mg/L) and in the other pond in Phung Hiep, Hau Giang (1.76 mg/L). The most common range of DO found in ponds was 5.02-7.66 mg/L (from 68% of total monitoring ponds). BOD and COD levels were obviously higher than those in rivers. There were only two ponds at the first sampling period having BOD levels greater than 10 mg/L which is the upper limit determined in the common regulations for surface water quality. Typically, BOD concentrations were low (4.30 mg/L in average, with a common rage of 1.04-7.68 mg/L). COD levels ranged from 1.6 to 28.8 mg/L. The highest level of COD is still below the upper limit (30 mg/L) of the water quality regulations. Turbidity was relatively high, particularly a few ponds having too high turbidity (>100 NTU). There were 40% of ponds having turbidity exceeding 50 NTU which is considered the upper limit of turbidity in fish ponds. TAN concentrations were in acceptable range (0.03-6.17 mg/L). Highest TAN level measured in the culture ponds was 6.17 mg/L. Based on data of temperature and pH recorded in this pond, NH3 concentration calculated from a table given by Robinette - (1983) was around 0.5 mg/L which is practically considered safe for fish. Nitrite (NO2 ) concentrations were relatively low. Averagely, these levels were in range with the recommended levels (<1 mg/L, Boyd et al., 2000), although there was only one pond having high concentration of nitrite (2.01 mg/L) in Phung Hiep, Hau Giang. There were more than 50% of the ponds having relatively low concentrations of nitrite, ranging from 0.01 to 0.08 mg/L. Another 40% of ponds contained a nitrite concentration of less than 0.5 mg/L which is considered safe level to fish. Nitrate concentrations in the culture ponds although were highly variable (from 0.09 to 8.1 mg/L), mean value was considered 3- suitable (2.32 mg/L). Dissolved phosphorus (PO4 ) concentrations were much higher than that in the rivers. More than 70% of ponds contained a phosphate concentration of greater than 0.1 mg/L, in which a range of 0.16-1.18 mg/L was commonly found. In average, TSS levels were suitably low (average of 55.3 mg/L, less than the upper limit of 100 mg/L). There were only two particular ponds (8%) having higher TSS levels, up to 120 and 138 mg/L. High levels of total nitrogen and phosphorus were recorded in the culture ponds. The mean TN (10.54 mg/L) and TP (3.01 mg/L) concentrations were triple and 30 times higher
11 than the recommended levels (10 mg/L and 0.1 mg/L, respectively) by Boyd and Green (2002). There were up to 44% of the culture ponds having TN and TP levels exceeding the mean concentrations, in which in some particular ponds, TN and TP were extremely high (28.2 and 9.46 mg/L, respectively). Details in variation of water parameter concentrations in the ponds are described in Table 5 and Appendix 2.
Table 5: Water parameters recorded in the culture ponds of the catfish production systems presented with values of mean, max and min of all 9 selected catfish ponds of crop 1. Parameters Mean Std. Max Min Temperature (oC) 30.1 1.33 32.0 27.9 pH 7.14 0.52 8.79 6.30 DO (mg/L) 6.20 2.03 9.91 1.76 BOD (mgO2/L) 4.30 3.46 12.2 0.16 COD (mgO2/L) 10.0 6.59 28.8 1.60 Turbidity (NTU) 54.7 44.8 170 7.00 Alkalinity (mg CaCO3/L) 78.8 26.5 161.5 48.5 Hardness (mg/L) 46.6 12.8 76.0 25.0 TAN (mg/L) 2.34 2.19 6.17 0.03 NO2- (mg/L) 0.24 0.44 2.01 0.01 NO3- (mg/L) 2.32 2.62 8.10 0.09 PO43- (mg/L) 0.71 1.15 5.15 0.02 TSS (mg/L) 55.3 31.7 139 20.4 TN (mg/L) 10.54 7.41 28.82 0.29 TP (mg/L) 3.01 2.77 9.46 0.16
c) Discharged canal (outlet) water Temperature in the discharged areas was slightly lower than that in the culture ponds, ranging from 26.8 to 29.6 oC. pH was also less variable in this system. Dissolved oxygen (DO) concentrations were averagely high (6.81 mg/L). There was only one site having very low DO levels (1.90 mg/L) and logically coincided with high BOD (13.5 mg/L) was recorded at this site. All the rest sampling sites had reasonably low BOD concentrations with a mean value of 4.81 mg/L. COD concentrations were low lying in an acceptable range of 1.2-15.6 mg/L which was lower than that of culture ponds. In comparison with ponds, turbidity in the discharged areas was even lower (average of 47.8 - - NTU compared to 54.7NTU in ponds). TAN, NO2 and NO3 levels were similar to those in ponds, lying in the acceptable limits (Table 6). Interestingly, TN and TP concentrations of this system were significantly lower than those in the ponds.
Table 6: Water parameters recorded in the outlets (discharged areas) of the catfish production systems presented with values of mean, max and min of all 9 selected catfish ponds of crop 1 Parameters Mean stdev Max Min Temperature (oC) 29.6 1.49 31.6 26.8 pH 6.99 0.31 7.58 6.76 DO (mg/L) 6.81 2.52 9.75 1.90 BOD (mgO2/L) 4.81 4.21 13.5 0.48 COD (mgO2/L) 9.00 4.79 15.6 1.20
12 Turbidity (NTU) 47.6 41.5 120 13.0 Alkalinity (mg CaCO3/L) 84.3 23.6 120 57.0 Hardness (mg/L) 46.3 9.27 58.5 30.5 TAN (mg/L) 2.63 2.48 5.91 0.07 NO2- (mg/L) 0.26 0.24 0.77 0.01 NO3- (mg/L) 2.39 2.48 7.36 0.15 PO43- (mg/L) 0.42 0.25 0.91 0.04 TSS (mg/L) 46.1 25.9 95.1 16.9 TN (mg/L) 6.94 3.25 12.1 2.14 TP (mg/L) 1.27 0.86 2.46 0.13
The values of some water quality parameters such as turbidity, alkalinity, hardness, nitrite, nitrate, TAN, TN and TP in ponds and discharge water were greatly increased if compared to river (inlet) water (Fig. 3 and Fig. 4). This indicated that striped catfish pond produces nutrients and turbidity that could be potentially impacting the water resources from its effluents.
Figure 3: Variation of some physical and chemical parameters representing water quality in rivers (inlets), ponds and discharged canals (outlets).
13
Figure 4: Variation of some water parameters representing for nutrient contents in rivers (inlets), ponds and discharged canals (outlets).
d) Assessment of water quality in the study catfish production systems Comparison of some parameters representing for nutrient contents between inlets, culture ponds and outlets indicated that the concentrations of most of parameters in ponds seems to be higher (Figure 4). In general, no obvious increased tendency of all water parameters through time at inlets (rivers/canals), culture ponds or outlets (discharged canals) was found in the catfish production systems. However, COD and TP concentrations increased steadily from the first to the third sampling periods. TN was significantly high at the beginning and gradually decreased to the end of production cycle. In contrast, TP levels increased over time toward the end of culture duration (Fig. 5). Except TN and TP, other parameters were in acceptable or suitable ranges. Mean values of water parameters measured in the inlets, culture ponds and outlets of the catfish production systems by time are presented in Table 7, 8 and 9. The percentage of samples having major water parameters exceeding recommended levels were also presented in Table 10. Percentage of sites (ponds) having exceeding
Table 7: Water parameters measured in the inlets (rivers/canals) of the catfish production systems through culture periods. Data presented with mean±stdev of total 9 sampling sites
Parameters Beginning Middle End Temperature (oC) 28.6±0.60 30.8±1.10 30.4±1.11 pH 7.12±0.12 7.55±0.61 6.76±0.26 DO (mg/L) 5.13±1.71 6.84±1.65 6.38±2.45 BOD (mgO2/L) 9.09±1.81 1.80±0.98 3.08±1.95 COD (mgO2/L) 6.29±2.93 9.29±6.61 13.6±7.24 Turbidity (NTU) 46.5±21.1 38.4±51.62 77.4±45.5 Alkalinity (mg CaCO3/L) 70.4±19.5 72.1±15.1 92.1±35.8 Hardness (mg/L) 33.9±8.38 51.7±11.82 51.2±10.25 TAN (mg/L) 1.40±1.47 1.45±1.79 3.96±2.24 NO2- (mg/L) 0.09±0.10 0.09±0.06 0.50±0.68 NO3- (mg/L) 3.64±2.31 3.13±3.21 0.48±0.40 PO43- (mg/L) 0.33±0.37 1.22±1.72 0.50±0.68 TSS (mg/L) 34.1±11.3 61.9±29.7 65.9±38.19 TN (mg/L) 14.5±4.92 7.86±4.90 10.1±10.0
14 TP (mg/L) 0.62±0.45 3.61±2.58 4.26±3.01
Table 8: Water parameters measured in the culture ponds of the catfish production systems through culture periods. Data presented with mean ± std of total 9 sampling sites Parameters Beginning Middle End Temperature (oC) 28.0±0.52 30.5±0.98 29.8±0.77 pH 7.24±0.03 7.56±0.61 7.05±0.20 DO (mg/L) 7.67±1.42 7.31±2.07 7.34±1.64
BOD (mgO2/L) 7.85±0.50 1.40±0.81 2.32±1.83
COD (mgO2/L) 2.80±2.23 5.82±2.10 10.7±5.69 Turbidity (NTU) 39.5±29.3 17.4±8.37 51.3±31.4
Alkalinity (mg CaCO3/L) 52.3±3.21 67.2±3.89 58.4 ±7.02 Hardness (mg/L) 24.4±3.01 44.1±6.53 40.7±5.43 TAN (mg/L) 0.22±0.23 0.12±0.14 0.46±0.47 NO2- (mg/L) 0.02±0.01 0.06±0.01 0.17± 0.33 NO3- (mg/L) 1.84±1.00 1.41±0.56 0.32±0.18 PO43- (mg/L) 0.11±0.17 0.30±0.21 0.17± 0.33 TSS (mg/L) 32.9±21.5 60.4±31.4 43.8±24.4 TN (mg/L) 9.69±3.87 3.94±1.19 4.15±5.68 TP (mg/L) 0.35±0.33 1.36±0.68 1.78±1.31
Table 9: Water parameters measured in the outlets (discharged areas) of the catfish production systems through culture periods. Data presented with mean±stdev of total 9 sampling sites Parameters Beginning Middle End Temperature (oC) 27.5±1.03 30.1±0.33 30.4±1.23 pH 7.19±0.55 7.07±0.27 6.79±0.05 DO (mg/L) 5.83±5.55 6.37±1.87 7.90±0.49
BOD (mgO2/L) 10.8±3.90 1.55±0.98 4.11±1.15
COD (mgO2/L) 9.20±1.13 4.80±4.33 13.1±3.11 Turbidity (NTU) 38.0±25.5 22.3±12.9 79.7±54.2
Alkalinity (mg CaCO3/L) 70.8±19.5 75.7±8.95 102±30.3 Hardness (mg/L) 33.8±4.60 49.0±5.77 51.8±6.51 TAN (mg/L) 2.51±2.56 0.23±0.15 5.10±0.70 NO2- (mg/L) 0.02±0.02 0.35±0.36 0.33±0.05 NO3- (mg/L) 1.52±0.22 4.81±2.60 0.55±0.35 PO43- (mg/L) 0.32±0.41 0.57±0.30 0.33±0.05 TSS (mg/L) 37.0±22.9 35.7±17.75 62.7±33.3 TN (mg/L) 9.97±3.01 7.91±2.26 3.95±1.80 TP (mg/L) 0.80±0.63 0.96±1.08 1.89±0.53
15 24 Beginning 22 Middle Rivers/Inlets 20 18 End 16 14 12 mg/L 10 8 6 4 2 0
24 Ponds 22 20 18 16 14
mg/L 12 10 8 6 4 2 0
24 Outlets 22 20 18 16 14 12 mg/L 10 8 6 4 2 0 DO BOD COD TAN NO2! NO3! PO43! TN TP
Figure 5: Variation of some water parameters representing for nutrient contents in rivers/inlets, ponds and discharged canals (outlets) between culture periods (beginning, middle and end of production cycle).
16 Table 10: Percentage of major water parameters beyond the recommended levels for aquaculture systems in crop-1. Parameters Unsuitable levels % of river % culture % discharged (based on Boyd (1998; Boyd water pond water water & Green 2002; TCVN 5942- samples samples samples 1995; Circular number (sites) (sites) (sites) 02/2006/TT-BTS; Le Van Cat et al, 2006) Temperature >32oC 8 8 0 pH <6.5 0 4 0 DO <2 mg/L 0 8 12.5 BOD >10 mg/L 0 8 12.5 COD >20 mg/L 0 4 12.5 TAN >3 mg/L 0 40 50 - NO2 >1 mg/L 4 8 0 TSS >80 mg/L 12 16 12.5 Turbidity >80 NTU 8 28 25 TN >10 mg/L 16 48 25 TP >0.1 mg/L 92 100 100 TP* >5 mg/L 0 16 0 *(PAD standard)
3.1.1.2 Phytoplankton Five phylum of algae were recorded including Chlorophyta (green-algae), Diatomeae (diatom belonging to Ochrophyta), Euglenophyta (euglenoids), Cyanobacteria (blue-green algae) and Dinophyta (dinoflagellates). Proportion of each phylum is presented in Figure 6., Total of 176 species found, in which Chlorophyta accounted for 40%, the most abundant algae with 72 species. The rests include diatom with 49 species, euglenoids 26 species, blue-green algae with 22 species and dinoflagellates only had 7 species (4%). Most of algae originated from freshwater source and green algae was the main group found in culture ponds. Most of the encountered algae are mainly species indicating for eutrophic environment. They were Actinastrum, Coelastrum, Pediastrum, Scenedesmus (Chlorophyta), Phacus, Euglena (Euglenophyta), Melosira, Cyclotella (Diatomeae), Spirulina and Oscilatoria (Cyanobacteria).
17 Dinoflagelle 4% Euglenoids" 15% Green 40% Blue!green 13%
Diatom 28%
Figure 6: Species compositions of algae recorded in all water samples of the catfish production system
Pond water was dominant with chlorophyta (33-58%) and euglenophyta (11-37%). chlorophyta (22-50%) and diatomeae (17-37%) were two most abundant groups in river water. Again, chlorophyta was also the most abundant group (covering 30-48%), but lower percentage if compared to ponds or rivers. Euglenophyta and cyanobacteria accordingly increased with higher proportions (16-38% and 11-25%, respectively). Differences in compositions of algae indicated that ponds and discharged areas were more rich in nutrient that induced growth of chlorophyta, euglenophyta and cyanobacteria, whereas in the rivers, more abundance of diatomeae as indicators for unpolluted environment. a) River (inlet) water There was no significant difference in species composition between 3 sampling periods. Four groups of algae were found including chlorophyta, diatomeae (ochrophyta), euglenophyta and cyanobacteria. Numbers of species decreased from the first sampling period with 20 species down to 13 species at the end (Figure 7). Chlorophyta was only dominant at the beginning of cropping while diatomeae was more abundant toward the end of culture periods (middle and the end of crop). Number of species of diatomeae increased with time but number of species from other groups decreased toward the end. Number of species at the beginning ranged from 14-27 species, in which the commonly found species were 14-21. Chlorophyta and diatomeae accounted for 32-65% and 14-42%, respectively. At the middle of cropping, number of species slightly decreased ranging from 11-27 species with 11-29 commonly found species. At the end of production cycle, number of species dramatically decreased to 9-15. The most common species found in most of sampling sites were Cyclotella, Melosira (diatomeae) and Pediastrum, Scenedesmus (chlorophyta).
18 25 Inlets/Rivers 20 Diatom
species 15 " Green of " 10 Euglenoid Blue!green
Number 5 Dinoflag. Total 0 Beginning Middle End
Figure 7: Species composition of algae in rivers
Quantitatively, densities of algae in the rivers were relatively low, ranging from 328,889±177,24 to 973,88±874,378 ind./L. There was up to 80% of sites having algae densities of less than 1,000,000 cells/L (Figure 8) and about 20% of sites having algae densities of 1.3 millions to 3 millions ind/L at the beginning and the end of cropping, respectively. Two major algae groups recorded in this particular sites were diatom and green algae. In summary, algae in the rivers characterized with relatively high species composition and lower number of individuals and no significant variation between sampling periods. In addition, strong development of diatom both qualitatively and quantitatively has indicated that the water source in rivers around the catfish production systems may have not been polluted.
Beginning of crop 3,500,000 Middle of crop 1,600,000 3,000,000 1,400,000 2,500,000 1,200,000 1,000,000 2,000,000 800,000 ind./L ind./L 1,500,000 600,000 1,000,000 400,000 200,000 500,000 - - In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3 In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3
2,500,000 End of crop 2,250,000 2,000,000 1,750,000 1,500,000 1,250,000
ind./L 1,000,000 750,000 500,000 250,000 - In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3
Figure 8: Densities of algae in the rivers in 3 sampling periods 19
b) Culture pond water Species composition of culture ponds was not different from that of rivers through 3 sampling periods (Figure 9). However, variation of species number was different from the rivers. High number of species was recorded at the beginning of cropping (21) and decreased at the middle (14) but increased back at the end (19). Number of species at the beginning ranged from 18-30 in which 18-22 were commonly found. Among them green algae accounted for 70% (in 43-57% of total sampling ponds), followed by euglenoid with 16-22% (50% of ponds). During the middle of the culture, number of species decreased to 10-13 in which green algae were still major group (25-58%). At the end of the culture, species number increased again with 15-21 species. The more abundance of green and euglenoids in ponds (compared to green and diatom in rivers) has indicated that increased nutrient load occurring in ponds. In the other hand, the increase of nutrient load in intensive culture ponds could be the reason causing reduction in species number of most of algae groups at the end of culture period except the dominated groups. However, in case of green algae, strong growth of many species at the same time is their typical characteristic manifested by their increased species number at the end of the culture.
25 Culture"ponds
20 species "
of 15 Diatom " Green 10 Euglenoid Number Blue!gree 5 Dinoflag. Total 0 1 2 3
Figure 9: Species composition of algae in ponds
Densities of algae in ponds were much higher that those in rivers and varied significantly through sampling periods. Lower densities were recorded at the beginning (2.628,116±2.276,836 ind./L) and not significantly different from those in the middle of the cropping (3,232,905±3,620,584 ind./L), but increased substantially at the end (12,603,700±13,216,809 ind./L). At the beginning of culture, 50% of total pond numbers had very low densities of algae (<1 million ind./L), the remain 50% having algae densities of average level ranging from 2 to 5 millions ind./L. During the middle of culture period, algae densities increased but not significantly with similar percentage of 50% of less than 1 million ind./L and 50% of 3 to 10 millions ind./L. Toward the end of production cycle, 30% of total ponds contained algae densities of 1-1.5 millions ind./L, 45% maintained at 3.5-13 millions ind./L and particularly up to 20% had high densities of algae ranging from 28 to 38 millions ind./L. Green algae accounted for high proportion and significantly contributed to total algae densities in the ponds, with a mean value of 1.4 to 12 millions ind./L. Following green algae was diatom with densities of 600,000 to 800,000 ind./L (Figure 10). Euglenoids and blue-green algae were in low numbers and relatively stable at the end of production cycle. Differences in dominant species of algae and their densities between rivers and culture ponds may indicate that water environment in ponds were much
20 richer in nutrient than that of rivers. However, as green algae dominated over euglenoid and blue-green algae in number, the water environment may be considered eutrophic but still not polluted.
8,000,000 Beginning of crop 8,000,000 Beginning of crop
6,000,000 6,000,000
4,000,000 4,000,000 ind./L ind./L
2,000,000 2,000,000
- - P2-1 P2-2 P2-3 P2-1 P2-2 P2-3 P 1-1 P 1-2 P 1-3 P 3-1 P 3-2 P 3-3 P P 1-1 P 1-2 P 1-3 P 3-1 P 3-2 P 3-3 P
14,000,000 End of crop 12,000,000 10,000,000 8,000,000
ind./L 6,000,000 4,000,000 2,000,000 - P2-2 P2-3 P 1-1 P 1-2 P 1-3 P 3-2 P 3-3 P
Figure 10: Densities of algae in the ponds in 3 sampling periods c) Discharged canal water The variation of algae species number was relatively similar to that of the ponds (from 18 species at the beginning decreased to 11 at the middle and increased to 20 at the end). The number of species recorded at the beginning, middle and the end of production cycle was 17-21, 10-12 and 20-22 species, respectively. Green algae were also the major group in the discharged areas consisting of 2-12 species, accounting for 12-71%. Euglenoids and blue-green algae in this system were higher in species number (14-33% and 17-30%, respectively) as compared to rivers and ponds (Figure 11.
25 Discharged!canals 20
15 Diatom species " Green of " 10 Euglenoid Blue!green 5
Number Dinoflag. 0 Total Beginning Middle End Figure 11 Species composition of algae in discharged canals
21 Mean algae density in this system was relatively high (4,426,987 ± 5,455,944 ind./L). There was significant variation in algae densities during the sampling periods (Figure 12. Algae densities dropped at the middle of cropping (770,826 ±1,022,160 ind./L) and increased dramatically at the end (9,241,000 ± 8,101,817 ind./L). Green algae accounted for highest numbers and increased at the end of culture period (8.475.426±7.391.965 ind./L). Highly increased densities and dominance of high nutrient preference species such as green algae, euglenoids and blue-green algae in the discharged areas may indicate that the areas were fairly rich in nutrient. In summary, variation of algae species compositions between rivers, culture ponds and discharged canals was not significantly different and tended to increase toward the end of production cycle. Chlorophyta (green algae) was the major group that substantially contributed to the variation. However, densities of algae were different between sites, in which lowest densities were normally found in the rivers and highest densities recorded in the ponds followed by the discharged canals.
12,000,000 Middle of crop Beginning of crop 10,000,000 10,000,000 8,000,000 8,000,000 6,000,000 6,000,000 ind./L ind./L 4,000,000 4,000,000 2,000,000 2,000,000 - - OutL1-1 OutL1-2 OutL1-3 OutL1-1 OutL1-2 OutL1-3
End of crop 18,000,000 16,000,000 14,000,000 12,000,000 10,000,000 8,000,000 ind./L 6,000,000 4,000,000 2,000,000 - OutL1-1 OutL1-2 OutL1-3
Figure 12 Densities of algae in the discharged canals in 3 sampling periods 3.1.1.3. Zooplankton Total of 99 species of zooplankton were recorded in the catfish production systems. They belong to 4 main zooplankton groups including Protozoa, Rotifera, Cladocera and Copepoda. There was additionally a small group of larval forms of Mollusca, Annelida, Nematoda and Ostracoda. Rotifers were the most abundant group with highest species numbers (42 species, accounting for 42%), followed by Protozoa (32 species, accounting for 32%). a) River (inlet) water Species compositions of zooplankton in the rivers were fairly abundant and generally decreasing from the beginning to the end of production cycle, là 22±3, 19±5 and 16±6 species, respectively (Figure 13). Rotifera always dominated with highest number of species in most of sampling site (80%) with 42 to 75% total zooplankton species. Densities
22 of zooplankton were also higher at the beginning of cropping (128,913±128,176 ind./m3) and decreasing gradually toward the end of culture period. The results indicated that water in the rivers was not too rich in nutrient.
Protozoa Cladocera 500,000 Beginning of crop 25" Rotifera Copepoda 450,000 Others Total 400,000 20" 350,000 300,000 15" 250,000 species "
Ind./m3 200,000 of " 10" 150,000 100,000 5" 50,000 Number 0 !
Beginning Middle End In1-1 In1-2 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3 In1-3
120,000 300,000 Middle of crop End of crop 100,000 250,000
80,000 200,000
60,000 150,000 Ind./m3 Ind./m3 40,000 100,000
20,000 50,000
0 0 In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3 In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3 Figure 13: Species compositions (left upper conner) and densities of zooplankton through the 3 sampling periods (beginning, middle and end of crop) in rivers (ln1-1, In2-1, In3-1, etc… stand for inlets (rivers) 1 of system 1, 2, 3, respectively, etc…)
At the beginning of culture, water source in the rivers contained a range of zooplankton density varying from 38,182-469,688 ind./m3, commonly from 38,182 to 74,667 ind./m3, accounting for 60% of total zooplankton in the river system. From this period onward, the most common densities of zooplankton encountered were less than 100,000 ind./m3, accounting for 100% at the middle and 80% at the end of culture periods (Figure 13). The most commonly zooplankton groups found in the rivers were Difflugia, Tintinnopsis (Protozoa), Brachionus, Filinia (Rotifera), Diaptomus and nauplius (Copepoda). b) Culture pond water The number of species and individuals tended to decrease gradually from the beginning to the end of production cycle. Numbers of species recorded at the beginning, middle and the end were 16±3, 15±5 and 11±5 corresponding to densities of 993,963 ±1,049,038, 712,056±1,133,855 and 221,663±484,481ind./m3, respectively (Figure 14). Species composition of zooplankton in the ponds was relatively lower than that of rivers but number of individuals was higher. This may be obvious that nutrient was supplemented in the ponds and those species that prefer high nutrient environment could grow well and increase their densities. At the beginning of culture period, the species number was fairly high varying from 11 to 20 species. The most common numbers found in most of ponds were 15 - 20 species (70% of total number of ponds). Rotifera always dominated with highest species numbers 23 (9-13 species in 70% of total pond numbers). Some larval stages of other groups were occasionally found such as larval forms of Mollusca, Annelida, Nematoda and Ostracoda. The densities of zooplankton varied significantly between ponds. However, the most common densities recorded ranging from 170,000 to 860,000 ind./m3, accounting for 60% of the ponds. Another 30% of the ponds having very high densities of zooplankton at the beginning, varying in a range of 1.4 millions to 3.6 millions ind./m3. High densities of zooplankton coincided with dominance of Tintinnopsis, a rich nutrient indicator protozoa or Brachionus, a relatively high nutrient indicator rotifer indicated that the environment was of rich organic or nutrient loaded. Significant variation between species numbers in ponds was found at the middle of culture period. A range of 7 to 21 species was recorded but commonly from 14 to 19 species accounting for 55% of the ponds. Rotifers were still the predominant groups. Densities were lower compared to the beginning with a common range of 120,000 – 600,000 ind./m3 (44% of the ponds). Particularly, there were about 44% of the ponds containing predominant species such as Anuraeopsis and Polyarthra (rotifers) which are indicator species for high nutrient loaded environment. In most of the ponds, densities of rotifers were high, accounting for 50-90% that determined high densities of zooplankton in ponds. At the end of production cycle, obvious reduction of species number was noticed, ranging from 4-16 species in which the most common species were 12 to 16, accounting for 67% of the ponds. Cladoceran was found with only one species (Moina rectirostris) which significant reduced as compared to the beginning (7 species) and middle (5 species). In contrast, the number of protozoan species was increasing. In some ponds, their number of species increased to 11 accounting for 70% of the total zooplankton species in the ponds. Densities of zooplankton were also decreasing at the end. A mean density was recorded as 221,663 ± 484,481 ind./m3 but the common range was of 35,000 to 140,000 ind./m3, accounting for 80% of the ponds. While rotifers were dominant at the beginning (55%) and middle (59%), protozoa took over in the end of culture period (51%). The results, thus suggested that the catfish ponds were fairly rich in nutrients resulting in diversified and abundant zooplankton species with high densities. The most commonly found species of zooplankton in the catfish ponds were Difflugia and Tintinnopsis (protozoan), Moina and Diaphanosoma (cladoceran), Anuraeopsis, Brachionus, Filinia, Keratella, Polyarthra and Trichocerca (rotifers), Eucyclops, Mesocyclops (copepod)
Protozoa Cladocera 1,800,000 Beginning of crop 25" Rotifera Copepoda 1,600,000 Others Total 1,400,000 20" 1,200,000 1,000,000 15" species
" 800,000 Ind./m3 of " 10" 600,000 400,000 5" 200,000 Number - !
Beginning Middle End P1-1 P1-2 P1-3 P2-1 P2-2 P2-3 P3-1 P3-2 P3-3
24 4,000,000 Middle of crop 1,600,000 End of crop 3,500,000 1,400,000 3,000,000 1,200,000 2,500,000 1,000,000 2,000,000 800,000 Ind./m3 1,500,000 Ind./m3 600,000 1,000,000 400,000 500,000 200,000 - - P3-1 P1-1 P1-2 P1-3 P2-1 P2-2 P2-3 P3-2 P3-3 P1-1 P1-2 P1-3 P2-1 P2-2 P2-3 P3-1 P3-2 P3-3
Figure 14: Species compositions (left upper conner) and densities of zooplankton (in total) through 3 sampling periods (beginning, middle and end of crop) in ponds (P1-1, P2- 1, P3-1,etc… stand for pond 1 of system 1, pond 1 system 2, pond 1 system 3, etc…)
c) Discharged canal (outlet) water The species composition of zooplankton in this system was similar to the ponds as it decreased with time. In average, the number of species found in this system was 20±11, 18±4 and 13±9 for the beginning, middle and the end, respectively (Figure 15). Protozoan and rotifers were predominantly recorded. Mean density reached highest at the middle of culture period (740,933 ± 799,380 ind./m3), in which rotifers dominantly accounted for 66%. Two mostly predominant rotifer species (genus) found in this system were Anuraeopsis and Philodina. Lowest density was recorded at the end of culture duration (102,833 ± 63,122 ind./m3). In contrast to the middle period, rotifers were not dominant in the end period, instead protozoa were taking over (41%) with density of 48,632 ± 57,254 ind./m3. Similar to the ponds, the variation of species composition and densities of zooplankton have suggested that water quality in the discharged areas tended to be richer in nutrient or polluted toward the end of the production cycle. The most common species found in these areas were Centropyxis, Difflugia and Tintinnopsis (protozoan), Moina (cladoceran), Anuraeopsis, Brachionus, Filinia, Keratella, Lecane, Polyarthra, Trichocerca, Philodina and Ploesoma (rotifers) and Eucyclops (copepod).
Protozoa Cladocera 1,800,000" D1!1 Rotifera Copepoda 25 1,600,000" D1!2 Others Total 1,400,000" D1!3 20 1,200,000" 15 1,000,000" 800,000" 10 Ind./m3 600,000" Number ofspecies Number 5 400,000" 200,000" - ! Beginning Middle End Beginning Middle End
Figure 15: Species compositions (left) and densities of zooplankton in discharged canals through 3 sampling periods of culture duration. D1-1, D1-2 and D1-3 stand for discharge canals 1, 2 and 3 of system 1.
25 In summary, most of water parameters were still in acceptable ranges for aquaculture, specifically for catfish culture. TN and TP concentrations in both rivers and culture ponds appeared to be much higher than recommended levels, indicating potential eutrophication and pollution. Data of phytoplankton and zooplankton relatively linked to the nutrient concentrations in the systems and also indicating certain levels of nutrient richness and potential pollution in the systems
3.1.2. Crop 2 3.1.2.1 Water physical and chemical characteristics
a) River (inlet) water Similar to crop 1, temperature recorded during the second crop was also in expected range varying from 28.6 ± 1.46 to 30.1 ± 1.81oC from the beginning to the end of the crop. Temperature tended to slightly increase with sampling periods and not significantly variable between systems and sites. pH was also in normal range with average value of 7.21 ± 0.38. There was no significant difference in pH between sampling periods during the culture duration. Mean value of DO in this crop was slightly lower than that of crop 1 (5.51 ± 1.59 mg/L compared to 7.42 ± 1.69, respectively). There were more than 83% of sites having DO concentration exceeding 4 mg/L. BOD levels were generally low with a mean concentration was 4.28 ± 1.45 mgO2/L. The maximal concentration recorded was only 8.27 mgO2/L. Similarly, COD concentrations were also in the suitable range from 3.60 to 12.73 mgO2/L. These values were insignificantly higher than those in crop 1. Most of sites (73%) had low BOD levels of less than 5 mg/L. For COD, more than 86% of sampling sites possessed a COD level of less than 10 mg/L. Nitrogen compounds were also low. TAN, nitrite and nitrate concentrations all were in suitable levels with mean values of 0.51 ± 0.34, 0.05 ± 0.07 and 1.37 ± 1.89 mg/L, respectively. Total nitrogen (TN) concentration was relatively low compared to that of crop 1 although the mean value was slightly higher than the recommended levels (3.92 ± 2.950 mg/L). Particularly, there was one site having a very high TN level, up to 14.42 mg/L. Total phosphorus (TP) concentrations were also high in all sites with a mean concentration of 1.28 ± 0.71 mg/L. The most common range of TP was from 0.97 to 1.90 mg/L accounting for 53%. Sites having TN and TP exceeding recommended levels (>3 mg/L and 0.1 mg/L, respectively) accounted for high proportion in total sampling sites at rivers (67 and 97%, respectively). Data of water parameters recorded in inlets/rivers are presented in Table 11. Variation of some major parameters through sampling period and systems are performed in Figure 16, 17 and 18.
Table 11: Water parameters recorded in the inlets (rivers) of the catfish production systems presented with values of mean, max and min of all 10 selected sites of crop 2 Parameters Mean Std Max Min Temp (oC) 29.3 1.54 31.9 26.7 pH 7.21 0.38 7.67 6.30 DO (mg/L) 5.51 1.59 8.70 2.77 BOD (mg/L) 4.28 1.45 7.82 2.11 COD (mg/L) 7.59 2.34 12.7 3.60 Turbidity (NTU) 83.3 45.4 175 20.0 Alkalinity (mg/L) 55.9 18.51 82.0 0.00 Hardness (mg/L) 43.8 14.35 66.0 15.50
26 TAN (mg/L) 0.51 0.34 1.38 0.02 NO2- (mg/L) 0.05 0.07 0.28 0.00 NO3- (mg/L) 1.37 1.89 8.41 0.00 PO4 (mg/L) 0.16 0.21 0.83 0.00 TSS (mg/L) 34.6 23.9 108 3.20 TKN (mg/L) 2.50 2.80 14.05 0.19 TN (mg/L) 3.92 2.95 14.42 0.70 TP (mg/L) 1.28 0.71 3.08 0.06
b) Culture pond water Water temperature was not significantly variable among culture ponds, ranging in suitable levels (29.84 ± 1.32oC). pH was also stable ranging from 6.5-8.5 in which more than 83% of site having the common range of 7.1-7.9. Dissolved oxygen concentrations were lower compared to that of crop 1. Mean DO level was 3.78 ± 1.53 mg/L which was much lower than that of crop 1 (6.20 ± 2.03 mg/L). The most common range of DO was 3.0 -5.68 mg/L (66%). There was up to 26% of ponds having DO concentration less than 3 in which 10% of ponds containing very low DO levels (less than 2 mg/L). BOD and COD concentrations in culture ponds were relatively higher than those in rivers, however, they were still in the accepted ranges. BOD levels ranged from 3.15 to 8.51 mg/L with mean value of 5.22 ± 1.57 mg/L and COD levels ranged from 4.65 to 14.4 mg/L with mean value of 9.13 ± 2.70 mg/L. In general, BOD and COD levels in the culture ponds were considered low and indicating low organic matter contents recorded during the sampling periods. Turbidity in ponds was high ranging from 108 ± 49.6 NTU, most of ponds having high turbidity (above 80 NTU) accounting for 73% of total sampling ponds. Concentrations of TAN, nitrite and nitrate were low ranging in the acceptable range, although a few ponds having very high nitrate concentration (34.93 mg/L). However, TKN levels were relatively high (5.54 ± 5.59 mg/L) leading to high levels of TN. Most of ponds contained high TN concentrations ranging from 3.02 to 35.96 mg/L, accounting for 83% of sampling ponds. TN levels in ponds of this crop were fairly lower than those in crop 1 (8.79 ± 8.56 mg/L compared to 10.54 ± 7.41 mg/L, respectively). TP concentrations were high with the mean values of 1.67 ± 1.09 mg/L that more than 10 times higher than the recommended levels suggested by Boyd and Green (2002). Considering TP concentrations of above 0.1 mg/L TP are the high level, there were up to 96.7% of sampling sites having TP level beyond this point. Details in variation of water parameters recorded in culture ponds are presented in Table 12. Table 12: Water parameters recorded in the culture ponds of the catfish production systems presented with values of mean, max and min of all 10 selected sites of crop 2 Parameters Mean Stdev Max Min Temp (oC) 29.8 1.23 32.5 27.7 pH 7.41 0.40 8.50 6.48 DO (mg/L) 3.78 1.53 7.57 0.12 BOD (mg/L) 5.22 1.57 8.51 3.15 COD (mg/L) 9.13 2.70 14.40 4.65 Turbidity (NTU) 109 49.3 232 35.0 Alkalinity (mg/L) 67.5 20.4 110 26.5 Hardness (mg/L) 49.7 40.9 244 6.90 TAN (mg/L) 2.63 2.32 7.55 0.01
27 NO2- (mg/L) 0.18 0.37 2.01 0.00 NO3- (mg/L) 3.38 6.66 34.93 0.04 PO4 (mg/L) 0.47 0.74 3.20 0.00 TSS (mg/L) 56.6 37.5 174 8.80 TKN (mg/L) 5.24 5.59 26.88 0.48 TN (mg/L) 8.79 8.56 35.9 0.59 TP (mg/L) 2.07 1.87 8.81 0.05
c) Discharged canals/outlets water Temperature and pH values were similar to those of ponds and rivers with mean temperature and pH of 29.69 ± 1.67oC and 7.13 ± 0.39, respectively. DO, BOD and COD levels were normal in which DO was relatively higher than that in ponds (4.63 ± 1.58 mg/L). BOD and COD levels were low lying in the suitable ranges (4.39 ± 1.25 mg/L and 8.24 ± 2.25 mg/L, respectively). There was no any exceptional case exceeding recommended level for these two parameters. It is obvious that turbidity in this system was very high ranging from 78-220 NTU and 89% of sites having turbidity of above 80 NTU. TSS levels were also high in this system with a mean value of 87.88 ± 45.42 mg/L. TN and TP concentrations of this system were also high but relatively lower than those found in the ponds ranging from 1.30- 23.10 mg/L (mean 7.25 ± 6.67 mg/L) for TN and 0.23 -3.42 mg/L (mean 1.67 ± 1.09 mg/L) for TP. Details in variation of water parameters recorded in culture ponds are presented in Table 13. Similar to crop 1, parameters exceeding recommended levels in crop 2 are mainly TSS, turbidity, TN and TP and presented in Table 14. Number of samples (sites) having exceeding levels of TN and TP in crops 2 is relatively lower than that of crop 1. In both crops, TP concentrations were very high compared to the recommended levels and most of the sites possessed the exceeding levels of TP.
Table 13: Water parameters recorded in the culture ponds of the catfish production systems presented with values of mean, max and min of all 10 selected sites of crop 2 Parameters Mean Stdev Max Min Temp (oC) 29.69 1.67 32.52 27.47 pH 7.13 0.39 7.53 6.31 DO (mg/L) 4.63 1.58 7.53 2.95 BOD (mg/L) 4.39 1.25 6.16 3.15 COD (mg/L) 8.24 2.25 11.60 4.73 Turbidity (NTU) 139.15 47.16 220.00 78.00 Alkalinity (mg/L) 67.22 21.67 93.00 25.00 Hardness (mg/L) 45.72 18.27 72.50 15.00 TAN (mg/L) 2.95 2.49 6.94 0.35 NO2- (mg/L) 0.09 0.11 0.36 0.01 NO3- (mg/L) 4.66 7.41 22.64 0.05 PO4 (mg/L) 0.44 0.59 1.73 0.00 TSS (mg/L) 87.87 45.42 175.00 35.00 TKN (mg/L) 2.49 2.47 7.82 0.45 TN (mg/L) 7.25 6.67 23.10 1.30
28 TP (mg/L) 1.67 1.09 3.42 0.23
Inlets Ponds
200.00 180.00 160.00 140.00 120.00
value 100.00 80.00 60.00 40.00 20.00 0.00 Temp"(oC) pH TSS"(mg/L) Turbidity"(NTU)Alkalinity"(mg/L)Hardness"(mg/L)
Figure 16: Variation of some physical and chemical parameters representing water quality in rivers (inlets), ponds and discharged canals (outlets).
Inlets Ponds
20.00 18.00 16.00 14.00 12.00 10.00 mg/L 8.00 6.00 4.00 2.00 0.00 DO BOD COD TAN NO2! NO3! PO4 TKN TN TP
Figure 17: Variation of some physical and chemical parameters representing water quality in rivers (inlets), ponds and discharged canals (outlets).
29 Beginning of crop
25.00 Inlets Ponds Outlets
20.00
15.00 mg/L 10.00
5.00
0.00
Middle of crop
100.00 Inlets Ponds Outlets 90.00 80.00 70.00 60.00 50.00 mg/L 40.00 30.00 20.00 10.00 0.00
End of crop
30.00
Inlets Ponds Outlets 25.00
20.00
15.00 mg/L 10.00
5.00
0.00 DO BOD COD TAN NO2- NO3- PO4 TKN TN TP
Figure 18: Variation of some water parameters representing for nutrient contents in rivers/inlets, ponds and discharged canals (outlets) between culture periods (beginning, middle and end of production cycle) during crop 2.
30 Table 14: Percentage of major water parameters beyond the recommended levels for aquaculture systems in crop 2. Parameters Unsuitable levels % of river % culture % discharged (based on Boyd (1998; Boyd water pond water water & Green 2002; TCVN 5942- samples samples samples 1995; Circular number (sites) (sites) (sites) 02/2006/TT-BTS; Le Van Cat et al, 2006) Temperature >32oC 0 3.3 3.3 pH <6.5 10 3.3 11 DO <2 mg/L 0 10 0 BOD >10 mg/L 0 0 0 COD >20 mg/L 0 0 0 TAN >3 mg/L 0 40 55.6 - NO2 >1 mg/L 0 0 0 TSS >80 mg/L 6.7 20 44.4 Turbidity >80 NTU 46.7 73.3 88.9 TN >10 mg/L 3.3 30 11.1 TP >0.1 mg/L 96.7 96.7 100 TP * >5 mg/L 0 7 0 *(PAD standard)
d) Changes in concentration of water parameters between inlets/rivers with ponds and discharged areas The differences in concentration of water parameters from rivers (source of water) to ponds and discharged areas are calculated and displayed as percentages of changes. Percent changes between inlets/rivers and outlets/discharged areas Changes between inlets and outlets (discharged canals) varied significantly among systems and sampling periods (Table 15). Temperature increased negligibly 1-2% during the culture periods and crops. Whereas, pH in most of sampling areas was decreasing, especially in crop 1 as maybe due to raining. Big changes were recorded for most of factors, particularly nutrient related parameters such as nitrogen and phosphorus. BOD and COD concentrations were also increasingly changed. The percentage changes of 3- parameters were more obvious in crop 1 than crop 2. TAN and PO4 even increased up to 2,775% and 2,525%, respectively. Reversely, DO concentrations decreased as negative % changes were recorded. These figures indicated that water quality is worse when coming out from the ponds as DO concentration decreasing but organic matter and dissolved nutrient increasing substantially. However, in crop 2, % changes (increases) of most of water parameters were lower.
31 Table 15: % changes of water parameters from inlets/rivers to outlets/discharged areas in catfish production systems of crop 1 and crop 2. ToC pH DO BOD COD TAN NO2 NO3 Crop 1 Beginning 2.02 -1.83 -36.9 30.17 386 2187 28.8 518 Middle 1.11 -2.35 -21.66 -12.12 16.1 247 432 249 End 2.38 -5.87 -1.00 19.38 -13.3 2775 1286 67.1 Crop 2 Beginning 2.19 -1.34 -22.89 9.78 19.61 201.10 -40.9 154.49 Middle 0.14 3.07 -25.72 6.89 16.52 122.35 168 143.72 End 1.48 0.90 6.04 6.20 15.59 470.09 167 -87.06 PO4 TN TP Turbiidty TSS Alkalinity Hardness Crop 1 Beginning 2525 118 516 151 246 55.8 46.8 Middle 123 81.3 -9.73 91.4 -29. 5 14.9 20.0 End 1286 64.1 5.64 27.1 23.1 63.2 31.2 Crop 2 Beginning 51.1 136 73.1 70.2 126 6.83 14.40 Middle 41.5 129 25.5 44.9 126 19.2 -5.34 End 232.4 44.5 67.2 24.9 226 15.7 12.1
Percent changes between inlets/rivers and culture ponds Similar to differences between discharged areas and rivers, changes of temperature between inlets and ponds were not great ranging in only a few percentage of increase. pH decreased in crop 1 but increased in crop 2. DO concentrations were also decreasing, sometimes up to 50%. However, BOD and COD concentrations were mostly increasing in the ponds. COD concentrations increased highest in system 3 at the beginning with nearly 192%. However, in crop 2, % change of COD was lower, less than 36% of increase. TAN levels increased substantially in ponds in crop 1. In system 1 at the end of crop, TAN increased up to 2,999% compared to the initial level in the inlets/rivers. In system 2 and 3 also at the middle of crop TAN concentrations increased extremely high, above 1000%. However, in crop 2, TAN increased more slightly from the inlets to ponds. % increase (change) of TAN between inlets and ponds was tremendous as the absolute figures in the inlets at the beginning were very low compared to the values recorded in ponds although they were still in the acceptable ranges. However, for TN and TP though their % increase between two sources was not that high but the absolute values were exceeding the recommended levels. Details of % change in concentrations of water parameters between inlets/rivers and culture ponds are illustrated in Table 16.
32 Table 16: Percent changes (increases) of water parameters between inlets/rivers and culture ponds in different culture periods in the catfish production systems Crop 1 ToC pH DO BOD COD TAN NO2 NO3 System 1 Beginning 2.75 -2.74 -37.72 35.93 164.29 1,367.74 445.04 92.01 Middle 3.45 -1.52 -18.70 -3.03 58.06 188.86 121.90 259.68 End 1.85 -6.33 -16.01 29.46 -16.81 2,998.55 1,544.21 142.29 System 2 Beginning 1.35 -0.37 -22.19 -5.33 89.29 77.61 815.94 81.76 Middle 1.39 3.20 11.25 40.00 38.89 1,734.34 22.75 (30.32) End 1.62 -3.08 -8.45 44.59 20.00 113.64 796.23 56.55 System 3 Beginning 2.13 -1.74 -51.91 12.64 191.67 63.99 157.79 492.15 Middle -1.16 -1.97 -8.19 60.78 84.78 1,149.81 (22.81) 176.43 End 3.02 -2.80 -15.25 25.86 101.37 720.98 0.73 (29.82) Crop 2 System 1 Beginning 2.62 7.38 -32.40 34.19 28.53 338.65 57.55 285.54 Middle 2.25 3.90 -52.15 27.61 35.67 212.71 900.40 163.22 End 1.45 1.35 -11.73 24.74 35.29 543.76 238.33 30.62 System 2 Beginning 2.19 3.02 -54.07 13.01 4.83 (7.96) 160.28 0.82 Middle 0.62 4.16 -22.35 10.37 10.21 102.04 91.07 2.96 End 0.50 1.32 -16.80 18.98 8.46 143.78 300.78 8.36 System 3 Beginning 2.47 1.38 -25.08 25.37 26.81 109.92 120.67 (29.98) Middle 1.95 2.32 -23.38 39.14 29.81 76.14 422.00 164.67 End 1.37 0.94 -38.41 12.29 11.90 105.07 141.40 249.76 Crop 1 PO4 TN TP Turbidity TSS Alkalinity Hardness System 1 Beginning 1,316.28 95.69 203.25 44.03 37.81 49.39 37.66 Middle 70.58 197.70 116.79 8.57 (3.56) 14.94 20.41 End 1,544.21 101.09 39.08 (4.79) 1.66 51.47 27.85 System 2 Beginning (13.88) 57.15 (1.32) (38.53) (2 4.61) 9.71 29.93 Middle 439.26 (31.59) 120.86 44.74 (41.67) 1.53 (0.36) End 796.23 114.98 97.74 100.00 90.54 9.60 7.23 System 3 Beginning 576.23 33.30 (3.50) 118.78 84.78 23.16 37.50 Middle 381.11 160.31 259.03 330.43 51.17 5.77 32.59 End 0.73 173.69 340.17 77.27 71.18 117.70 40.61 Crop 2
1 System 1 Beginning 131.59 261.75 8.37 24.69 100.00 41.01 37.45 Middle (87.30) 172.76 (8.55) 22.92 74.62 11.35 (0.31) End 341.95 199.78 118.22 9.55 88.88 16.91 16.98 System 2 Beginning 104.65 14.84 178.31 51.52 31.91 72.16 (32.38) Middle 171.96 92.06 (5.57) 55.11 35.83 21.50 4.60 End 650.00 53.18 68.47 16.80 22.63 18.57 (3.68) System 3 Beginning (80.04) 40.62 40.36 108.97 65.78 10.19 (14.42) Middle 233.17 129.13 36.98 19.81 51.30 16.63 (13.46) End 1,228.04 132.52 107.02 36.36 158.33 16.02 162.45
2 3.1.2.2. Phytoplankton There were 166 species recorded in the catfish production systems, also belong to 5 groups including green algae (Chlorophyta), diatom (Diatomeae), euglenoids (Euglenophyta), blue-green algae (Cyanobacteria) and flagellates (Dinophyta) (Figure 19). Green algae also dominated with high number of species (72 species accounting for 43%) followed by diatom (50 species, 30%). The most commonly found species were Pediastrum, Scenedesmus (Chlorophyta), Phacus, Euglena (Euglenophyta), Melosira, Cyclotella, Nitzschia (Diatomeae), Spirulina và Oscilatoria (Cyanobacteria). There is no difference in species compositions of algae between 2 crops.
Blue!Green"" Dinoflagella" 7% 3% Diatom" Euglenoids"" 30% 17%
Green"43%
Figure 19: Species compositions of algae recorded in the rivers systems
Species composition and proportion of algae between 2 crops were similar to those in crop 1. Green algae were the most common group encountered in rivers, culture ponds and discharged canals ranging from 30-55%, followed by euglenoids with 10-28% especially in pond and discharged canals. However, diatom was more dominant in the rivers with high proportion (27-41%, after green algae). These results revealed that ponds and discharge canals may contain more nutrient than rivers as diatom abundance in the rivers indicating unpolluted environment. a) Rivers/inlets water Number of algae species in the rivers/inlets tended to decrease from 32±6 at the beginning to 25± 4 species at the middle and increased back to 32±6 species at the end of crop. (Figure 20). In all 3 sampling periods, green algae were always higher in number of species (12-15) followed by diatom (6-8) that determined the variation of species compositions in the rivers. At the beginning, the number of species varied from 24 to 38, the most common range was 27-39 species accounting for 90% of total sampling sites. Green algae and diatom accounted for 30-49% and 20-47%, respectively. At the middle of crop, number of species was more variable ranging from 14-42 and the most common numbers encountered was 14-25 accounting for 70% of sampling sites. Diatom and green algae were still the dominant groups with 30-41% and 30-37%, respectively. At the end of crop, slightly increase in number of species was observed with 29-49 species. The most commonly found species were Cyclotella (diatom) and Pediastrum, Scenedesmus (green algae).
1
40 Rivers
30 Diatom Green species " 20
of Euglenoid " Blue!green 10 Dinofla Number Total 0 Beginning Middle End
Figure 20: Species composition of algae in rivers
Densities of algae recorded were lower than those in crop 1. Densities of less than 1 million ind./L (indicating oligotrophic conditions) were common in most of sampling sites, up to 80% (Figure 21). There were only 20% of sites having algae densities of more than 1.1 -2 million ind./L during 3 sampling periods. Mean algae densities at the beginning, middle and end of crop were not significantly variable and tended to increase toward the end with 612,374 ± 604,778 ind./L; 452,192 ± 316,971ind./L and 887,251 ± 478,292 ind./L, respectively. Green algae were the dominant group with a mean density of 482,292±108,333 ind./L.
2,500,000" Ind/L Beginning 2,000,000" 1,500,000" 1,000,000" 500,000" ! Inlet" Inlet" Inlet" Inlet" Inlet" Inlet" Inlet" Inlet" Inlet" Inlet" 1!1 1!2 1!3 2!1 2!2 2!3 3!1 3!2 3!3 3!4
2,500,000 Middle of crop
2,000,000
1,500,000
ind./L 1,000,000
500,000
- In1-1 In1-2 In1-3 In2-1 In2-2 In2-3 In3-1 In3-2 In3-3 In3-4
2 2,500,000 Ind/L End 2,000,000
1,500,000
1,000,000
500,000
- Inlet Inlet Inlet Inlet Inlet Inlet Inlet Inlet Inlet Inlet 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4
Figure 21: Densities of algae in the rivers in 3 sampling periods
b) Culture ponds Species number and compositions of algae in catfish ponds of crop 2 were not much variable during the 3 sampling periods. The number of algae species at the beginning, middle and the end of crop were 31±5, 32±6 and 30±5 (Figure 22). Green algae contained highest number of species in all sites with 14, 16 and 15 species at the beginning, middle and end of crop, respectively. The total number of species at the beginning was 19-40 in which the most common seen species were 28-40 accounting for 70% of total ponds in which green algae presented up to 70% of ponds accounting for 43-50%, followed by euglenoids and diatom with 18-28% and 18-30% accounting for 60% and 50%, respectively. Blue-green algae presented with a few species, commonly 3-5 species in 90% of sites. At the end of crop, green algae also dominated with 43-74% of total 30-39 algae species. The accumulation of nutrient from left-over feed and fish wastes resulted in increased nutrient levels. This in turn induced growth of high nutrient preferable algae species of Chlorophyta group leading to high number of species.
35 Culture!ponds 30 . 25
20 Diatom 15 Green Species Euglenoid 10 Blue!green 5 Dinofla Total 0 Beginning Middle End
Figure 22: Species composition of algae in ponds
Densities of algae at the beginning were highly variable between culture ponds ranging from 248,278 to 6,463,778 ind./L. The most common densities recorded in most of ponds were from 1,107,556 to 6,463,778 ind./L, accounting for 70% of total ponds. Green algae were always the dominant groups representing to 40-97% of total individuals with many species preferring in oligotrophic conditions such as Scenedesmus, Pediastrum, Chlorella, Coelastrum, Phacus. At the middle of crop, algae densities in ponds were 3 decreasing in which 20% of ponds having densities of less than 1 million ind./L and 80% of them having densities of 1.7-3.4 million ind./L. at the end of crop, as accumulation of nutrient increased algae densities also increased again with 50% of ponds having 2.5-6.6 million ind./L and particularly 10% of them with high densities up to 12.3 million ind./L. Green algae were still dominated with high densities followed by diatom with densities ranging from 60,000-5.7 million ind./L. Densities of euglenoids and flagellates were low and not increased at the end of crop.
12,000,000 Total Beginning 10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
- P 1-1 P 1-2 P 1-3 P2-1 P2-2 P2-3 P 3-1 P 3-2 P 3-3 P 3-4
12,000,000 Total Middle 10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
- P 1-1 P 1-2 P 1-3 P2-1 P2-2 P2-3 P 3-1 P 3-2 P 3-3 P 3-4
12,000,000 Total End 10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
- P 1-1 P 1-2 P 1-3 P2-1 P2-2 P2-3 P 3-1 P 3-2 P 3-3 P 3-4
Figure 23: Densities of algae in the ponds in 3 sampling periods
There was no any significant difference in species compositions and densities of algae between crop 1 (dry season) and crop 2(rainy season). There were also 5 main groups of algae found in which green algae was the dominant group presenting in all water 4 bodies during 3 sampling periods of each crop. However, number of species in crop 1 was higher than that of crop 2 (44±5 compared to 18±3 species, respectively). There was no significant difference in algae densities between beginning and middle of crop. However, at the end, the common densities in the first crop (1,617,778-6,600,028 ind./L, accounted for 80% of samples) were much lower than those in the second crop (12,314,000- 38,544,250 ind./L, accounting for 50%). Green algae always dominated in most of culture ponds and determined algae densities in the systems both two crops. The most commonly found algae species were Chlorella, Scenedesmus, Coelastrum, Pediastrum, Crucigenia (Chlorophyta); Cyclotella, Nitszchia, (Diatom); Phacus, Euglena (Euglenophyta).
c) Discharged canals/outlets Number of algae species at the beginning, middle of end of crop were 19-33, 20-31 and 25-28, respectively (Figure 24), in which green algae were also the dominated group with highest number of species and densities. Species number of this group increased through time from beginning to end of crop accounting for 46%, 52% and 55% of the total algae species, respectively. Number of species of diatom also increased from the beginning to end of crop (12%, 23% and 25%, respectively). In contrast, number of euglenoid species decreased from the beginning to the end of crop (22%, 17% and 10%).
30"
25"
20" Diatom
15" Green
Species Euglenoid 10" Blue!green Dinofla 5" Total ! Beginning Middle End Figure 24: Species composition of algae in discharged canals
Mean algae densities in this system were relatively high (3,328,870± 3,8,27,485 ind./L). There was a big variation in densities between sampling periods (Figure 25), very high at the beginning (5,230,130 ind./L), but decreased at the middle (955,741ind./L) and increased again at the end of crop (3,800,741 ind./L). Green algae was also the group having highest densities in three periods accounting for 56-91% of total algae densities. There was no significant difference in algae densities between two crops. However, the density of algae in discharged canals of crop 1 (9,241,000 ind.L) was much higher than that of crop 2 (3,800,741ind./L) especially at the end of crop
5 12,000,000 Beginning 12,000,000" Middle 10,000,000 10,000,000" 8,000,000 8,000,000" 6,000,000 6,000,000" 4,000,000 4,000,000" 2,000,000 2,000,000" ! - OutL1-1 OutL1-2 OutL1-3 OutL1!1 OutL1!2 OutL1!3
12,000,000" End 10,000,000" 8,000,000" 6,000,000" 4,000,000" 2,000,000" ! OutL1!1 OutL1!2 OutL1!3
Figure 25: Densities of algae in the discharged canals in 3 sampling periods Similar to crop 1, there was significant difference in algae species composition in rivers/inlets, culture ponds and discharged canals/outlets. Algae species composition and densities of these 3 systems increased at the end of crop. Green algae was also the major group that determined the variation of algae in the water bodies. Densities in rivers/inlets were lower than those in ponds and discharged canals. There were significant difference in both species number and densities of algae in inlets, ponds and outlets between crop 1 and 2. Densities of algae in inlets and ponds were not significantly variable between two crops with mean densities of 601,109 ind./L and 4,426987 ind./L (crop 1); 629,618 ind./L and 3,328,870 ind./L (crop 2). While, in the culture ponds, mean algae densities of crop 1 was higher than that of crop 2 (5,927,535 ind./L compared to 2,757,225 ind./L, respectively.
d) Changes of species number and densities of phytoplankton between inlets, ponds and outlets (discharged canals) In system 1, the mean number of species increased from inlets to ponds (14% in crop 1 and 44% in crop 2). However, it varied through sampling period (Table 17). Densities of algae in ponds were also significantly higher comparing to inlets with approximately 30 times (3,000%) in crop 1 and 18 times (1,800%) in crop 2. In discharged canals, mean number of algae species in both crop did not change significantly in comparison with inlets (12% and 6% of increase in crop 1 and crop 2, respectively). Mean densities of algae in this system were 19 times (1,900%) and 10 times (1,000%) higher compared to inlets for crop 1 and 2, respectively. Lower species number and densities of algae in inlets compared to ponds and discharged canals suggested that there was an increase in nutrient levels from inlets to ponds and discharge canals. In system 2, the mean species number of algae increased 19% in ponds compared to inlets in crop 1. However, in crop 2 the species number decreased 14%. Nevertheless,
6 densities of algae in ponds increased in both crops (13 (1,300%) and 5 times (500%) higher than those in inlets for crop 1 and 2, respectively). Thus, less variation in species number and densities of algae was observed in this system compared to system 1. Similarly, increase in species number and densities of algae in ponds was also observed in system 3. % increase of both these factors was 16 and 25% for crop 1 and 2, respectively. Mean densities of algae increased in ponds with 8 (800%) and 18 times (1,800%) higher than in inlets in crop 1 and crop 2, respectively. Table 17: Percent changes of species number and densities of phytoplankton from inlets/rivers to ponds and outlets/discharged canals in catfish production systems of crop 1 and crop 2. % change between inlets and outlets Crop 1 Number of species Densities System 1 Beginning 0.81 380.05 Middle -39.26 166.37 End 73.89 4906.87 Crop 2 System 1 Beginning -7.86 2060.58 Middle 31.34 96.13 End -5.48 407.77 % change between inlets and ponds Crop 1 System 1 Beginning 18.21 254.88 Middle -30.53 1877.87 End 54.44 6598.14 System 2 Beginning 1.21 618.33 Middle -4.83 545.69 End 60.56 2379.62 System 3 Beginning 17.62 352.14 Middle -24.40 849.11 End 82.78 4010.63 Crop 2 System 1 Beginning 14.25 4433.88 Middle 97.28 104.84 End 21.22 430.37 System 2 Beginning -8.93 139.75 Middle -0.52 746.16 End -33.09 311.32 System 3 Beginning -9.60 786.71 Middle 30.83 854.65 End 11.22 328.87
3.1.2.3. Zooplankton A total of 89 species of zooplankton were obtained in catfish production systems in crop 2, belonging to 5 groups including protozoa (22), cladocera (12), rotifera (41), copepoda (9) and larvae of other groups such as Mollusca, Annelida, Nematoda, Mysidacea và Ostracoda.
7 Total number of species found in catfish production systems in crop 2 (dry season) were relatively lower than that of crop 1 (rainy season). Rotifera was the most dominant group and the number of species was not different between two crops (42 and 41, respectively). However, species number of protozoa was significant difference between two crops (32 in crop 1 but only 22 in crop 2). a) Rivers/Inlets Species number of zooplankton increased at the middle (23±4) and end of crop (20±5) (Figure 26). The common number of species found at the beginning in all sampling sites was 12-19 (60%), at the middle was 18-24 accounting for 90% of sampling sites. Similarly, at the end of crop common range of number of species was found to be 20-24, accounting for 60%. Rotifera was the most dominated group (10-13 species) and composing the species composition of zooplankton in the sampling sites. The other groups including protozoa, cladocera and copepoda were in low number, about 4-5, 1-2 and 2-3 species, respectively. Similar to crop 1, highest mean densities were obtained at the beginning of crop (170,492±211,749 ind./m3) and decreased toward the middle (130,257±104,140 ind./m3) and end of crop (93,052±103,961 ind./m3). At the beginning, densities of zooplankton varying from 15,833-724,500 ind./m3, common range was 62,727-276,571 ind./m3, accounting for 70% of total sampling sites. Densities decreased from the middle to the end of crop with the most commond densities of 100,000 ind./m3, accounting for 50-70% of total sampling sites. The most coomonly found genera were Difflugia, Tintinnopsis (protozoa), Anuraeopsis, Brachionus, Polyarthra, Notholca, Trichocerca (Rotifera) and nauplius of copepoda. In general, water in the rivers/inlets was average in nutrient and no significant difference was found in zooplankton species number and densities between crop 1 and 2.
700,000"
600,000"
500,000" Protozoa 400,000" Rotifera (ind./m3) " Cladocera 300,000" Copepoda
Densities 200,000" Nauplius 100,000" Others Total !
8 800000 800,000" Middle Beginning 700,000" 700000 600,000" 600000 500,000" (ind/m3) ! 400,000" 500000 300,000"
400000 Density 200,000" 100,000" 300000 ! Density (ind/m3) Density 200000 1!11!21!32!12!22!33!13!23!33!4 100000 0 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4
800,000 End 700,000 600,000 500,000 400,000
Density (ind/m3) Density 300,000 200,000 100,000 - 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4
Figure 26: Species compositions and densities of zooplankton in rivers b) Culture ponds Mean species number of zooplankton was 21±5 at the beginning and decreased at th end of crop (16±3) (Figure 27). The most common number of species was 17-23, 18-22 and 13-16 accounting for 70% of total sampling sites at the beginning, middle and end of crop, respectively. Rotifera was the most dominated group with highest mean number of species in all sites with 12, 13 and 10 species in the beginning, middle and end of crop, respectively. The species number of protozoa was not variable through sampling periods (3-4) whereas cladocera and copepoda were low in number of species and decreased to the end of crop. Mean densities were increasing at the middle of crop but sharply decreasing at the end of crop (560,482±341; 887, 970±639,194 and 148,338±137,635 ind./m3, respectively).
9 25
20 Protozoa Cladocera 15
species Rotifera " of " 10 Copepoda Others 5
Number Total
0 Beginning Middle End
2,100,000 2,100,000 Beginning Middle 1,800,000 1,800,000 1,500,000 1,500,000 1,200,000 1,200,000 900,000 900,000 Density (ind/m3) Density 600,000 600,000 Density (ind/m3) Density 300,000 300,000 - - 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4
2,100,000 End 1,800,000 1,500,000 1,200,000 900,000 Density (ind/m3) Density 600,000 300,000 - 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 3-4
Figure 27: Species compositions and densities of zooplankton in culture ponds
At the beginning of crop, species number of zooplankton was relatively high and variable between sampling sites ranging from 10-29 species. The most common range of species number was 17-23, accounting for 70%. Rotifera was the most dominant group with 10-15 species, accounting for 60% of sampling sites. Other groups including protozoa, cladocera and copepoda had lower species numbers of 1-3. Densities varied significantly between ponds ranging from 135,300-1,138,500 ind.m3 but the most common range was 135,000-780,000 cá th#/m3 accounting for 80% of total sampling ponds. Rotifera was dominating and accounting for 31-96% of total densities with dominated species such as Anuraeopsis fissa, Brachionus calyciflorus and Brachionus angularis. These species are present in high nutrient environments. There was only 20% of ponds having densities of more than 1 million ind./m3. Species number at the middle of crop ranged from 14-27 and commonly was 18-22 (70% of total ponds). During this time nutrient contents were increasing and densities of
10 zooplankton also increased accordingly ranging from 55,000-2,000,000 ind./m3, commly with 800,000-2,000,000 cá th#/m3, accounting for 50% of ponds. Rotifera was still dominated with 69% of total number of zooplankton. The most commonly species were Tintinnopsis fimbriata (Protozoa), Anuraeopsis fissa and Brachionus angularis (Rotifera). At the end of crop, species number and densities were significantly decreasing compared to the beginning. Number of species varied in range of 13-21, 70% of sampling ponds having 13-16 species. Species number of cladocera decreased significantly at the end of crop (mean 1±1 species), only 30% of ponds having cladocera occurrence. Similarly, number of species of copepoda also decreased sharply at the end of crop. Up to 80% of pond did not have occurrence of copepoda or only one species presented during this period. Whereas, species number of protozoa increased to the end of crop. Rotifers were still dominated with high densities at the end of crop but lower as compared to that of beginning and mid of crop. In contrast, percentage of high densities of protozoa tended to increase at the end of crop (15%, 23% and 26% for beginning, middle and end of crop, respectively). This indicated that murtient contents were also increasing at the end of crop. However, due to more frequent water exchange was implemented during this period, total densities of zooplankton decreased ranging from 20,842-419,444 ind./m3. There was about 80% of ponds having densities of 20,000-197,000 ind./m3. The most commonly found species were Difflugia, Tintinnopsis (Protozoa), Anuraeopsis, Brachionus, Epiphanes, Filinia, Polyarthra, Notholca, Trichocerca (Rotifera), Eucyclops and nauplius (Copepoda). There was no significant difference in species compositions and numbers of zooplankton between crop 1 and crop 2. Densities of zooplankton were not significantly variable at the beginning and end of crop. However, at the middle of crop, the common densities of crop 1 (800,000-2,000,000 ind./m3) were higher than those of crop 2 (120,000- 600,000 ind./m3). Rotifers were also the dominated group contributing to the total densities of zooplankton in both crops. c) Discharged canals/outlets Species numbers of zooplankton at the beginning, middle and end of crop were 24- 26, 20-22 and 17-19 accounting for 67%, 67% and 100% of total sampling sites, respectively. Densities of zooplankton were also increasing at middle of crop (420,455±520,678 ind./m3) (Table 17). Rotifers contributed with highest number of species and densities and increased from the beginning toward the end of crop accounting for 53%, 59% and 71% of total densities (Table 18 and 19). Densities of protozoa, however decreased toward the end of crop (38%, 33% and 19%, respectively. Table 18: Species number of zooplankton in discharged canals Beginning Middle End Protozoa 6 5 3 Cladocera 2 1 1 Rotifera 12 8 12 Copepoda 2 2 1 Others 0 1 2 Total 22 16 18
Table 19: Densities of zooplankton (ind./m3) in the discharged canals Beginning Middle End Protozoa 134,560 68,878 23,326 Rotifera 161,102 280,635 220,889
11 Cladocera 10,009 0 0 Copepoda 6,551 10,878 3,000 Nauplius 23,593 60,063 32,000 Others 1,361 0 0 Total 337,176 420,455 279,215
The most commonly found species were Difflugia, Tintinnopsis (protozoa), Anuraeopsis, Brachionus, Filinia, Polyarthra, Notholca, Trichocerca (rotifera) and nauplius (copepoda). Species compositions and numbers in discharged canals were not significantly different between two crops. However, mean densities of zooplankton at the beginning and middle of crop 1 (667,593±500,464 ind./m3 and 740,933±799,380 ind./m3, respectively) were higher than those of crop 2. In addition, dominated genera were found during crop 1 such as Anuraeopsis and Philodina but not in crop 2.
d) Changes of species number and densities of zooplankton between inlets, ponds and outlets (discharged canals) In system 1, mean number of species of zooplankton in ponds decreased 15% compared to that in inlets of crop 1, whereas in crop 2, it increased 5%. However, mean densities increased significantly with 7.5 times (7,500 %) in crop 1 and 17.5 times (17,500%) in crop 2. In the discharged canals, mean species number was higher than that in inlets with an increase of 2-15%. Similarly, mean densities of zooplankton also increased highly in the discharged canal from 8 times (800%) to 13 times (1,300%) in crop 1 and 2, respectively. Similarly to system 1, in system 2 species number of zooplankton also decreased in ponds compared to inlets in crop 1 (decrease of 19%) but slightly increased in crop 2 (increase of 10%). Mean densities in both crops also increased significantly in ponds with 28.5 times (2,850%) and 3.7 times (370%) for crop 1 and 2, respectively. In system 3, the number of species also reduced in ponds, lower than that of inlets by 40% and 19% in crop 1 and 2, respectively. However, densities increased in ponds with 540% in crop 1 and 360% in crop 2. Percent changes (increase or decrease) of species number and densities of zooplankton between inlets/rivers and pond and discharged canals/outlets is presented in Table 20.
Table 20: Percent changes of species number and densities of zooplankton from inlets/rivers to ponds and outlets/discharged canals in catfish production systems of crop 1 and crop 2. Percent change between inlets and outlets Crop 1 Number of species Densities System 1 Beginning -12.3 481.69 Middle 7.62 2811.53 End 11.6 281.20 Crop 2 System 1 Beginning 31.7 1082.99 Middle -19.9 0.52
12 End 32.2 1039.19 Percent change between inlets and ponds Crop 1 System 1 Beginning -28.1 209 Middle -21.5 1672 End 3.81 45.4 System 2 Beginning -8.85 3098 Middle 4.82 1968 End -22.7 3169 System 3 Beginning -31.7 425 Middle -39.7 375 End -48.5 -32.28 Crop 2 System 1 Beginning 16.6 2499 Middle -5.00 1988 End 2.31 467 System 2 Beginning 52.8 285 Middle 0.56 513 End -21.9 4.21 System 3 Beginning 5.29 444 Middle -12.7 730 End -20.2 143
3.2 Contaminants 3.2.1 Antibiotics The analysis of seven kinds of antibiotic residues from muscle of striped catfish showed that the highest level of contamination was 22.2% of samples collected from second samplings of crop-1 (n=63). The levels of contamination of other sampling were low from 1.59 to 11.1% (Fig. 19). In addition, 11.1% of samples collected in the third sampling of crop-1 (before harvest) were contaminated. The results indicated that farmers used antibiotics during the first period of production cycle, and this is relevant with the results of questionaire interview, farmers responded that they use antibiotics at nursing stage and first few months of grow-out stage if disease occurrence. However, the concentrations detected, however were within the permitted range of European markets (less than 100 ppb). This result still raises attention of using antibiotics during the last period of culture cycle. The detected antibiotic residues were of encrofloxacine and norfloxacine, which are two main antibiotics used to treat the white spot on liver of striped catfish (Fig. 29).
13
Fig. 28: Percent of samples containing antibiotic residues (n=63 for crop-1 and n=70 for crop 2)
Fig. 29: Percent of samples contaminating antibiotic residues (n=27 for each antibiotic)) The residues of quinolone groups were found in all studied systems. The contamination was detected in 2nd and 3rd sampling of crop-1, while it was in 1st and 2nd sampling of crop-2 (Fig 30). This result is indicated that the use of quinolone groups in striped catfish farming varied by the occurrence of the diseases in the culture systems.
14 Fig 30: Percentage of contaminated ponds with floquinolone group (crop-1 left and crop- 2 right)
The concentration of antibiotic residues detected from samples varied greatly. There were four samples of crop-1 containing encroloxacine of 1,863 ppb and norfloxacine 740; 743 and 1,501 bbp, which were extemely high. These values were excluded in Fig 31. These are hard to explaine but they could be analysis error or from the high use dose of farmers to treat fish diseases just before the sample collection.
160 Crop!1 140 Crop!2 120 (ppb) " 100 80 60 40 Concentration 20 0 Encro Cipro Norflox
Fig. 31: Concentration of antibiotic residues detected from collected samples
3.2.2 Heavy metals
Five main haevy metals including Cupper (Cu), Arsenic (As), Cadmium (Cd), lead (Pb) and mercury (Hg) were selected to analyse from water samples. Cu was detected in all samples (crop-1 and crop-2) and Pb was also found in all samples of crop-1 and 65% samples of crop-1. Cd and As were found at low percentage in samples of crop-1 and crop- 2; they were 41.5% and 13.8%; and 17.4% and 8.70% for Cd and As in samples of crop-1 and crop-2, respectively (Fig 32). In contrast, Hg was not found in any collected sanples. In terms of concentration, the average detected concentrations of As and Pb were lower
15 than the levels of the Vietnamses standard for site selection of catfish cage culture (As $20 ppb; Pb$7 ppb, Cd$1800 ppb and Hg $100 ppb) (28 TCN 176: 2002) (Fig. 33).
100 90 Crop"1 80 70 Crop"2 (%) " 60 50 40 30
Contamination 20 10 0 Cd As Hg Pb Cu
Fig. 32: Percentage contaminated of samples by indicated heavy metal compared to analyzed samples (crop 1, n=65 and crop 2, n=69)
90 80 Crop"1 70 Crop"2 60 (ppb) " 50 40 30
Concentration 20 10 0 Cd As Hg Pb Cu
Fig. 33: Concentration of heavy metals in water samples collected from crop 1 and crop 2 3.2.3 Pesticides Twenty seven pesticides (9 of orthophosphorus and 18 of chlrine…) were analysed for levels of presentation in water samples. With the LOD (limit of detection, ppb) of the analytical instruments, none of pesticide residues was found from collected water samples, excepting one river sample was alpha endosulfan – 1 with the amount of 53.5 ppb This result indicated that levels of pesticides in water sources for striped catfish farming in the Mekong delta has no or very low level of pesticie residues.
16 Table 21: Pesticides contamination of samples collected from crop-1 and crop-2. Name of pesticides Limit of Supply canal Culture Discharge/ detection (ppb) pond settlement pond Organophosphorus pesticides Triethylphospo 20 ND ND ND Thionazin 50 ND ND ND Sulfotep 50 ND ND ND Phorate 50 ND ND ND Dimethoate 80 ND ND ND Disulfoton 50 ND ND ND Methyl parathion 50 ND ND ND Parathion 80 ND ND ND Farmphur 80 ND ND ND Organochlorine pesticides Aldrin 10 ND ND ND Endrin 80 ND ND ND Diendrin 20 ND ND ND Endrin aldehyte 50 ND ND ND Endrin ketone 80 ND ND ND Methocychlor 80 ND ND ND Heptachlor 50 ND ND ND Heptachlor epoxide 50 ND ND ND #-BHC 50 ND ND ND $-BHC 50 ND ND ND Delta-BHC 50 ND ND ND Gamma-BHC 50 ND ND ND 4,4 DDD 80 ND ND ND 4,4DDE 10 ND ND ND 4,4 DDT 20 ND ND ND #-endosulfan-I 10 ND ND ND $-endosulfan-II 50 ND ND ND Endosulfan sulfate 80 ND ND ND Notes: ND: not detected LOD: limit of detection (ppb)
3.2.4 Total bacteria and coliform There were obvious high variations found in the total bacteria counts in water samples collected at different sampling spots as well as in different culture systems. Crop variation in bacterial counts was also obvious. It is found that the total count in the second crop is lower then in the fist one (Table 22).
17 Table 22: Range of total bacteria count from water samples and coliform in fish specimens in 2 crops System Sample type Sampling spot Range (CFU/ml in water or CFU/g in fish) Total bacteral count Coliform Crop 1 1 Water Supply canal 1,850-53,500 - Culture pond 1,000-27,000 - Discharge/ 1,050-65,500 - settlement pond Fish Culture pond - 0–360 2 Water Supply canal 1,900-60,000 - Culture pond 1,000-57,000 - Fish Culture pond - 0-625 3 Water Supply canal 1,900-40,500 - Culture pond 3,650-66,000 - Fish Culture pond - 0-655 Crop 2 Water Supply canal 1,050-20,500 - 1 Culture pond 250-6,700 - Discharge/ 1,100-8,550 - settlement pond Fish Culture pond - 0-430 2 Water Supply canal 750-9,750 - Culture pond 750-6650 - Fish Culture pond - 0-975 2 Water Supply canal 500-18,650 - Culture pond 1,500-7,200 - Fish Culture pond - 0-440
In the supply canal, total bacterial count ranged from 1,850-60,000 CFU/ml for crop- 1 and from 500-20,500 CFU/ml for crop-2. In the culture pond, total bacterial count ranged from 1,000-66,000 CFU/ml in the crop-1 whereafter it ranged from 250–7,200 CFU/ml in the crop-2. Total bacterial count in discharge (or settlement) pond were very much higher in crop-1 (1,050-65,500 CFU/ml) compared to crop-2 (1,100-8,550 CFU/ml). Total bacterial count at different spots in culture system-2 displayed quite similar variation. However, high variation between sampling spots was found in system-1 (Table 22).
There variations found in the coliform counts in different sampling sites were also obvious between culture systems and crops. The coliform counts in all sampled culture pond ranged from 0–655 CFU/g in crop-1 and 0–975 CFU/g in crop-2. Of these, the coliform counts in 7 of 27 samples in crop-1 were !200 CFU/g and there were 7 of 30 samples in crop-2 had coliform counts !200 CFU/g.
In conclusions, total bacterial counts at all sampling spots were in acceptable ranges for aquaculture environment. Total coliform counts were acceptable in most of analyzed samples accept 14 samples that coliform counts !200 CFU/g.
18 REFERENCES 1. Boyd & Green, … 2002. ………….. 2. Boyd, C., 1998. …………….. 3. Circular number 02/2006/TT-BTS: ………… 4. Dung, N.H., 2008. Achieving a sustainable future for Vietnamese seafood industry. Keynote speak at the IIFET 2008 conference, Nha Trang, Vietnam. July 22-25, 2008. 5. Le Van Cat …………. , 2006: ………… 6. Liem, P.T., Phong, N.V.,Phuong, N.T., 2008. The use of drugs and chemicals in catfish farming in the Mekong River Delta, Vietnam: A review. Scientific Journal of Can Tho University, Viet Nam (in Vietnamese) (submitted). 7. Ministry of Fisheries (2002). Sector standard (28 TCN 176: 2002) for cage culture of Panasius bocourti and Pagasianodon hypophthalmus: required conditions for for food safety. 8. Phuong, N.T., Hoa, T.T.T., Ut, V.N., Giang, H.T., Anh, C.T., Hang, N.T.T., Thao, P.T.N., Thy, D.T.M., Thao, N.T.T., Oanh, D.T.H., Hau, N.M., Thinh, N.Q., Phuong, D.N., 2007. Study on environment and disease pathogens of catfish farming Tra (Pangasianodon hypophthalmus) and basa (Pangasius bocourti) and giant freshwater prawn (Macrobrachium rosenbergii) in An Giang province. Report submitted to An Giang Science and Technology Department, pp. 125 (in Vietnamese). 9. TCVN 5942-1995: ………….. 10. 28 TCN 176: 2002: 11. Tuan, N.A., Phuong, N.T., Liem, P.T.,Thuong, N.V., 2003. Results of the study on Pangasius catfishes and their future development. Journal of Mekong Fisheries. pp:129-134 (Vietnamese).
19