Water quality and plankton densities in mixed shrimp-mangrove forestry farming systems in Vietnam

Water quality and plankton densities were monitored in shrimp ponds at 12 mixed shrimp‐mangrove forestry farms in Ca Mau province, southern Vietnam, to detail basic water chemistry and assess whether conditions are suitable for shrimp culture. In general, water quality was not optimal for shrimp culture. In particular, ponds were shallow (mean ± 1SE, 50.5 ± 2.8 cm), acidic (pH < 6.5), had high suspended solids (0.3 ± 0.03 g l^?1), low chlorophyll a/phytoplankton concentrations (0.2 ± 0.05 µg l^?1 and 8600 ± 800 cells l^?1 respectively) and low dissolved oxygen (DO) levels (3.7 ± 0.15 mg l^?1). Eight out of the 12 farms sampled had potentially acid sulphate soils (pH < 4.2). Salinity, DO and pH were highly variable over short time‐periods (hours); DO in particular was reduced to potentially lethal levels (1–2 mg l^?1). Seasonal variations in water chemistry and plankton communities (i.e. salinity, DO, phosphate, temperature, phytoplankton and zooplankton densities) appear to be driven by differences in rainfall patterns. The presence or absence of mangroves on internal pond levees (‘mixed’ versus ‘separate’ farms) and the source of pond water (rivers versus canals) were of lesser importance in determining water quality patterns and plankton biomass. Zooplankton and macrobenthos densities were sufficient to support the current (low) stocking densities of shrimp. However, natural food sources are not adequate to support increases in production by stocking hatchery reared post larvae. Increasing productivity by fertilization and/or supplemental feeding has the potential for adverse water quality and would require improvements to water management practices. Some practical strategies for improving water quality and plankton densities are outlined.     

Biological characteristics of the improved extensive shrimp system in the Mekong delta of Vietnam

Low and unstable shrimp yields of the improved extensive shrimp system has been a tremendous obstacle for economic development in the coastal areas of Southern Vietnam. To investigate the biological characteristics of this system, ponds in the coastal Cai Nuoc district, Mekong delta of Vietnam, were monitored. Results showed that the system was not optimal for shrimp. While chlorophyll a (chl a) (1.51–37.2 μg L^?1), phytoplankton density (6333–974 444 cells L^?1) and zooplankton density (7.1–517.2 ind L^?1) were abundant and comparable to shrimp farms elsewhere, zoobenthic community was very poor (7–1971 ind m^?2). Toxin‐producing cyanobacteria (Oscillatoria limosa, Oscillatoria formosa, Anabaena sp. and Phormidium tenue) were found. Total bacteria and Vibrios were present in large numbers (respectively 1.04 × 10⁵ and 6.64 × 10² CFU mL^?1 in pond water, 6.33 × 10⁵ and 9.47 × 10³ CFU g^?1 in sediment). Presence of toxin‐producing organisms, poor zoobenthic community and abundance of Vibrios all can enhance shrimp susceptibility to diseases. The following measures are recommended to improve the situation: (1) complete testing of seeds for pathogens, (2) not to incorporate fish into shrimp ponds and (3) applying no‐culture breaks and pathogen‐killing chemicals.     

Physico‐chemical characteristics of the improved extensive shrimp farming system in the Mekong Delta of Vietnam

Consecutive failure of the improved extensive shrimp farming system has deterred the economy of some coastal areas in Vietnam. To investigate pond physico‐chemical characteristics, a monitoring scheme was performed in the Cai Nuoc district of Southern Vietnam. Results show that the system was not optimal for shrimps. While ponds were not contaminated by organic loadings or major nutrients (N, P) and salinity and pH were most optimal for shrimp, more than 37% of dissolved oxygen (DO) measurements were lower than recommended. In the early morning hours, DO measurements were even much lower (0.84–2.20 mg L^?1). Sulphate (SO₄^2?) concentrations were most within the acceptable range. Total suspended solids (TSS) were above the acceptable limit (<50 mg L^?1). Iron, alkalinity and hydrogen sulphide were also higher than recommended. Pond sediment was anaerobic (redox potential ?422 to ?105 mV) and contained high amounts of organic matter (9.84–21.96%). Lethal DO levels, high TSS and anoxic sediment are the drawbacks in this system. Suggested measures to improve pond conditions are (1) allowing sedimentation before filling culture ponds, (2) covering dikes, (3) including no‐culture breaks between shrimp crops, (4) drying pond bottom, (5) removing sediment and (6) controlling pond's vegetation.     

Current status of farming practices of striped catfish, Pangasianodon hypophthalmus in the Mekong Delta, Vietnam

Aquaculture of catfish, Pangasianodon hypophthalmus (Sauvage), locally known as “ca tra”, and commonly referred to as striped catfish, river catfish and sutchi catfish, in Vietnam, having recorded a production of 683,000 tonnes in 2007, valued at about 645 million US$ is one of the largest single species based farming system, restricted to a small geographical area, in the world. The product is almost totally exported to over 100 countries as frozen fillets, as an acceptable alternative to white fish. Catfish is farmed mostly in earthen ponds, up to 4 m deep, in nine provinces in the Mekong Delta in South Vietnam. The results of the grow-out system of catfish farming in the Mekong Delta from a survey of 89 farms are presented. The farm size ranged from 0.2 to 30 ha with a mean of 4.09 ha. The frequency distribution of the yield in tonne/ha/crop and tonne/ML/crop corresponded to a normal distribution curve, where 75% of the farms yielded 300 tonnes/ha/crop or more. It was found that the yield per crop was significantly correlated (p < 0.05) to stocking density, pond depth and volume but not to pond surface area. Yields per crop was significantly different (p < 0.05) between upper and lower provinces of the Mekong Delta and water source (river versus channels), amongst others. It was evident that diseases and/or symptoms were observed to occur mostly in accordance with the onset of rains. In this paper the history of the catfish farming in the Mekong Delta is briefly traced, and current harvesting and marketing procedures as well as pertinent social elements of the farming community are dealt with.     

Use of planted biofilters in integrated recirculating aquaculture‐hydroponics systems in the Mekong Delta,Vietnam

The feasibility of using planted biofilters for purification of recirculated aquaculture water in the Mekong Delta of Vietnam was assessed. The plant trenches were able to clean tilapia aquaculture water and to maintain good water quality in the fish tanks without renewal of the water. NH₄‐N was removed efficiently in the plant trenches, particularly in the trenches with Canna glauca L., probably because of plant uptake and nitrification–denitrification. Plant uptake constituted 6% of N and 7% of P in the input feed. Approximately 1.0 m³ of water was needed per kg of fish produced, and 370, 97 and 2842 g fresh aboveground biomass of Ipomoea aquatica Forssk., Lactuca sativa L. and C. glauca, respectively, were produced. The leafy vegetables provide some extra income besides fish products, whereas C. glauca provides nice flowers and contributes to a significant nutrient removal with annual uptake rates of 725 kg N and 234 kg P ha^?1 year^?1. This research demonstrates that integrated recirculating aquaculture‐hydroponics (aquaponics) systems provide significant water savings and nutrient recycling as compared with traditional fish ponds.     

Estimates of nutrient discharge from striped catfish farming in the Mekong River,Vietnam, by using a 3D numerical model

A simulation was carried out by using a 3D numerical model for estimate the nutrient level discharged from striped catfish, Pangasianodon hypophthalmus intensively farming in the Mekong River, Vietnam. The simulated period was dry season from April 24, 2007, to April 27, 2007. Both dissolved and particulate forms of nutrients were simulated. A real status of water environment and scenario of discharge after applying fishpond effluent for irrigation of rice field were estimated in My Hoa Hung fish farm, An Giang Province. Simulated results were verified by observed data. Our results showed that nutrient levels at farming area in dry season were temporarily high and local. Applying waste water from the fishpond for irrigation of rice field could greatly reduce nutrients level in the fish farming area, the nutrient levels were 77 % for total nitrogen and 73 % for phosphorus. Therefore, recycling nutrient from fishpond effluent for irrigation of rice field illustrated an effective technology for pollution reduction which is a crucial issue to enable sustainable development of intensively farmed striped catfish.     

Economic characteristics of extensive shrimp farms in the Mekong delta

Abstract

Extensive forms of shrimp aquaculture have become an important source of income for farm households in the brackish water region of the Mekong Delta, Vietnam. The economic and production characteristics of farms are discussed in this paper, based on a 1997 farm survey, with particular emphasis on shrimp farming practices. Two types of shrimp fanning practice were observed, one based on natural recruitment of seedstock with few supplementary inputs, and the other based on relatively high cash investments in Penaeus monodon seedstock and other inputs. Households practising monodon culture made significantly more income, but faced high risk associated with shrimp mortality. An investigation of the factors affecting monodon yields indicated that investment in higher quality inputs had a positive effect on yield and income. However, further research is needed on the extent to which management can reduce risk of shrimp mortality by investing in such premium quality inputs.     

Water and nutrient budgets of ponds in integrated agriculture–aquaculture systems in the Mekong Delta, Vietnam

A participatory on-farm study analysed water and nutrient budgets of six low and four high water-exchange ponds of integrated agriculture–aquaculture (IAA) farms in the Mekong delta. Water, nitrogen (N), organic carbon (OC) and phosphorus (P) flows through the ponds were monitored, and data on fish production and nutrient accumulation in sediments were collected during a fish culture cycle. Results showed that, on average, only 5–6% of total N, OC or P inputs introduced into ponds were recovered in the harvested fish. About 29% N, 81% OC and 51% P accumulated in the sediments. The remaining fractions were lost through pond water discharges into adjacent canals. Fish yields and nutrient accumulation rates in the sediments increased with increasing food inputs applied to the pond at the cost of increased nutrient discharges. High water-exchange ponds received two to three times more on-farm nutrients (N, OC and P) while requiring nine times more water and discharging 10–14 times more nutrients than the low water-exchange ponds. Water and nutrient flows between the pond and the other IAA-farm components need to be considered when optimizing productivity and profitability from IAA systems.     

Carbon and nitrogen budgets in shrimp ponds of extensive mixed shrimp–mangrove forestry farms in the Mekong delta,Vietnam

Mass balance estimates of carbon and nitrogen flux through two extensive shrimp ponds in the Mekong delta, Vietnam, were constructed to identify major sources and sinks of organic matter potentially available for shrimp production. Nutrient transformations in the sediments were measured to further assess rates of decomposition and burial and quality of organic matter. Tidal exchange was the major pathway for inputs and outputs of carbon and nitrogen in both ponds, with net primary production, nitrogen fixation and precipitation being minor inputs. No fertilizers or artificial feeds were added to either pond. The nutrient budgets identified burial and respiration as the next most important outputs after tidal exchange losses of particulate and dissolved carbon and nitrogen. There was no measurable denitrification in either pond, and volatilization was negligible. Mineralization efficiency of carbon in the water column was high (> 100%) in pond 23 reflecting rapid respiration rates; efficiency was lower (36%) in pond 12 waters. Mineralization efficiency of sediment nutrients averaged 34% for C and 41% for N in the pond with a higher annual shrimp yield (pond 12); lower mineralization efficiencies (11% for C, 10% for N) were calculated for the lower yield pond (pond 23). High burial efficiencies for both C (66–89%) and N (59–90%) in the sediments of both ponds suggest that little organic matter was shunted into biological production. Conversion efficiency for shrimp averaged 16% for C and 24% for N from pond 12, and 6% for C and 18% for N from pond 23. The high quantity but low quality of organic matter entering the ponds coupled with other factors, such as poor water quality, limits shrimp productivity. On average, nutrient outputs were greater than inputs in both ponds. This imbalance partly explains why shrimp yields are declining in these ponds.     

Evaluation of potential feed sources,and technical and economic considerations of small‐scale commercial striped catfish (Pangasius hypothalamus) pond farming systems in the Mekong Delta of Vietnam

A technical and socio‐economic survey was conducted in Dong Thap, Can Tho and An Giang, provinces of Vietnam in 2009. The results showed that most of the small scale farmers of striped catfish (Pangasius hypothalamus) carry out fish pond culture, developed and operated by self‐learned experience and from neighbours knowledge. The mean pond depth varied from 3.5 to 4.0 m, ranging from 2 to 6 m. Most of the fish farms have extremely high stocking density, with an average of about 40 fish m^?2, in some cases up to 70 fish per m². The average yields and net income of small‐scales pond farming is about 21–27 kg per m² crop^?1 and US$ 0.184–0.329 kg^?1 crop^?1 respectively. These figures are not significantly different compared with large‐scale pond farming. About 75%, 86% and 80% of fish farmers in Dong Thap, Can Tho and An Giang province, respectively, received positive net returns. Farm‐made feed is still playing an important role because of higher net profit compared with commercial pellet feeds. Rice bran and trash fish are the main feed ingredients for farm‐made feed formulations. Striped catfish farmers are now actively searching for locally produced plant protein sources as alternatives to marine trash fish or fish meal.     

Screening of quinalphos,trifluralin and dichlorvos residues in fresh water of aquaculture systems in Mekong Delta,Vietnam

To develop an easy and reliable method for detecting pesticides and their residues in the Mekong Delta, a GC‐MS analytical method was developed and validated according to European guidelines (SANTE/11945/2015) for the determination of residues of three pesticides (quinalphos, trifluralin and dichlorvos) in water. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.002 and 0.007 μg/L, respectively, for quinalphos and trifluralin, and 0.016 and 0.053 μg/L, respectively, for dichlorvos and quinalphos. The repeatability, the within‐laboratory reproducibility as well as the trueness met the European criteria. The recovery rate ranged between 72% (for dichlorvos and quinalphos) and 82% (for trifluralin). The developed method was then applied for the analysis of 33 water samples, collected in April 2013, at the beginning of the rainy season in the Mekong Delta in Vietnam. Thirteen samples were from rice field, 10 were collected from cat fish ponds and from red tilapia cages. Results showed that only 9% of total water samples analysed contained residues of pesticides, but only in water from rice fish systems. From the 13 samples taken in these systems, quinalphos was detected in three samples. The other two pesticides were not detected. A comparison between analytical results obtained from GC‐MS and an alternative method, that is GC‐ECD indicated that GC‐ECD is less sensitive than GC‐MS, with LOQ ranging from 0.37 to 1.18 (depending on the pesticide). However, for samples with concentrations above these LOQ, no significant difference was observed between the results obtained from the two analytical methodologies.     

新形势下稻渔综合种养模式的探索与实践

为全面掌握东北地区稻田养殖中华绒螯蟹 (Eriocheir sinensis) 的农药残留情况,利用气相色谱串联质谱法 (GC-MS/MS)和液相色谱串联质谱法 (HPLC-MS/MS)调查了东北三省主要稻-蟹产区中华绒螯蟹体内42种农药的残留水平,并采用食品安全指数法(IFS)评价了农药的潜在健康风险。在采集的56份样品中,除β-HCH、p, p′-DDE、乙氧氟草醚、丁草胺、乙草胺、莠去津等14种农药检出外,其余28种农药均未检出。其中,检出率最高的为β-HCH (89.3%)和p, p′-DDE (82.1%);检出农药含量最高的为乙氧氟草醚(256 μg·kg^–1)和丁草胺(185 μg·kg^–1)。健康风险评价结果表明,检出农药的IFS均远小于1,平均安全指数相似文献   

Biological Observations on the Mudskipper Pseudapocryptes elongatus in the Mekong Delta,Vietnam

Aspects of the population biology of the mudskipper, Pseudapocryptes elongatus, (Cuvier, 1816) were studied in Bac Lieu Province in the Lower Mekong Delta, Vietnam, including sex ratio, length–frequency distribution, sexual dimorphism, hepatosomatic index (HSI), female gonadosomatic index (GSI), gonad histology, fecundity and some observations on post‐larvae and juveniles. In the population studied the sex ratio was skewed toward males. Females had a shorter mean length and a lower mean growth rate than males. No mature males or females were observed among mudskippers sampled in estuarine canals from February to May 2004 during the dry season. It is suggested that P. elongatus migrates to the sea to spawn later in the year after onset of the wet season. Salinity tolerance was evaluated in a 96‐h experiment. This showed that P. elongatus is remarkably euryhaline and able to survive in salinities ranging from freshwater to 50 ppt. Gut content analysis revealed that P. elongatus is a herbivore, feeding mainly on pennate diatoms (93% of the diet).     

Effects of Integrated Shrimp Farming in Vietnam

Despite being a leading shrimp exporter in the world market, shrimp farming in Vietnam is carried out by many small‐scale farmers who face constraints in complying with increasingly stringent food safety and sustainability standards. The best way for such small farmers to circumvent this paradox is to make effective integrations both horizontally and vertically. Using value chain and institutional economics approaches, this study determines the factors that influence the probability of horizontal and vertical integrations between the production and processing stages in the shrimp industry in Vietnam. Analysis results confirm that integrated shrimp aquaculture is much more effective than the traditionally small‐scale‐ and individual‐production mode. In addition, logit estimation results identify the key factors affecting integration, including effectiveness of the legal framework, production scale, infrastructure development, and farmers' skill and awareness. Several policy recommendations proposed to encourage the development of integration in shrimp farming in Vietnam could also be useful for other similar developing countries.     

A closer look into shrimp yields and mangrove coverage ratio in integrated mangrove-shrimp farming systems in Ca Mau,Vietnam

Shrimp aquaculture is the biggest source of export income in Vietnam. However, the development of the shrimp poses a serious threat to coastal mangroves by converting coastal mangroves into shrimp farms. Much effort has been made to replant mangroves and reduce the impacts of shrimp farming on the environment, and maintaining mangrove coverage at 30–50% of total farm area has provided the highest benefits in the integrated mangrove shrimp model. In this study, we re-examine the benefits of forest cover on the survival and yield of tiger shrimp (Penaeus monodon) in the integrated mangrove shrimp farming systems in Ca Mau province, Vietnam. The study found positive linear correlations of log transformed survival and yield of tiger shrimp with forest cover of the forms: Ln (survival)?=????1.39?+?0.038?×?forest coverage (r²?=?0.22; p value?=?0.0007); Ln (yield)?=?3.55?+?0.026?×?forest coverage (r²?=?0.16; p value?=?0.004). The households with high forest cover (i.e.,?>?45%) also had 1.07?±?0.29 and 1.39?±?0.36 (CI 95%, p value?=?0.000) kg ha^?1 higher yield per night harvest than those with medium and low forest cover, respectively. As a result, households with high forest cover have higher benefits than those with lower forest cover. Our findings together with previous published studies lead to the recommendation that farmers maintain mangroves in farming systems for better economic and environmental benefits.

     

Rice with fish culture in the semi-deep waters of the Mekong Delta, Vietnam: a socio-economical survey

The results of a socio-economical survey of farming systems practising rice culture with introduced fish, rice culture with indigenous fish and rice monoculture in the semi-deep waters of the Mekong Delta, Vietnam, are presented. Rice and fish yields, inputs, and cost-benefits were computed to evaluate the agricultural effects of rice with fish culture. Household size, labour availability and educational level were not significantly different among the three farming systems. Rice-fish farming systems differed mainly from rice monoculture by a higher fertilizer/ water requirement and less pesticide use. The total farm cash and net return did not differ among the farming systems. The main beneficial effects of rice-fish culture are thought to be related to environmental sustainability, system biodiversity, farm diversification and household nutrition.     

Impacts of climate change on snakehead fish value chains in the Lower Mekong Basin of Cambodia and Vietnam

ABSTRACT

The productive fisheries of the Lower Mekong Basin of Cambodia and Vietnam are essential to the food security and nutrition of 60 million people. Yet these fisheries, both culture and capture, are susceptible to the impacts of climate change. This article reports on a study undertaken to examine the vulnerability, as perceived by snakehead (Channa striata) fish farmers in Vietnam and fishers in Cambodia, to the impacts from climate change. Perceived impacts on various actors in the value chain are identified, as well as adaptation strategies currently being utilized and planned for the future. Recommendations are suggested to contribute to assisting snakehead farmers and fishers in adapting and preparing for the impacts of climate change.     

Water pollution by Pangasius production in the Mekong Delta,Vietnam: causes and options for control

In this paper, we analyse water pollution caused by farming and processing Pangasianodon hypophthalmus in the Mekong Delta of Vietnam. The results show that 1 tonne of frozen fillets releases 740 kg BOD, 1020 kg COD, 2050 kg TSS, 106 kg nitrogen and 27 kg phosphorus, of which wastewater from fish ponds contributes 60–90% and sludge from fish ponds and wastewater from processing facilities contributes 3–27% of the total emissions. Overall, the combined waste emissions from Pangasius production and processing account for <1% of the total TSS, nitrogen and phosphorus loads in the Mekong Delta. Despite the relatively low contribution to water pollution, further reductions are possible through more efficient use of inputs and low-cost treatment and re-use of effluent streams. The use of cleaner production technologies and the development of wastewater treatment plants could be applied to large farms and processing facilities to reduce water pollution in Pangasius processing. Low-cost options for small-scale farms include the optimization of the discharge design for the re-use of wastewater.