173 research outputs found
Learning and communicating about the livelihoods of fishers and farmers
No full textCONTENTS: Approaches to understanding pond-dike systems in Asia: the POND-LIVE project approach, by Dave Little, Marc Verdegem and Roel Bosma. The contribution of fish ponds to nutrient cycling in integrated farming systems, by P.N. Muendo, J.J. Stoorvogel and Marc Verdegem. Improving the contribution of fishfarming to livelihoods in Northeast Thailand, by Chittra Arjinkit, Roel Bosma, Danai Turongrouang. Benefits of pond-dike systems in Bangladesh, by M.S. Kabir, M.A. Wahab and Marc Verdegem. Common carp increases rohu production in farmers ponds, by Mohammad Mustafizur Rahman, Md. Abdul Wahab and Marc C.J. Verdegem. Improving pond-dike farming systems in the Mekong delta, Vietnam; the Can Tho approach, by Dang Kieu Nhan, Le Thanh Duong, Le Thanh Phong, Roel H. Bosma and Marc C.J. Verdegem. Fuzzy pathways for farm development in Vietnam, by Roel H. Bosma, Le Thanh Phong, and Dang Kieu Nhan.The STREAM Initiative was hosted at the Network of Aquaculture Centres in Asia-Pacific (NACA) in Bangkok (Thailand
STREAM Journal, Vol. 6, No. 1, pp 1-21. Jan-March 2007
No full textCONTENTS: Approaches to understanding pond-dike systems in Asia: the POND-LIVE project approach, by Dave Little, Marc Verdegem and Roel Bosma. The contribution of fish ponds to nutrient cycling in integrated farming systems, by P.N. Muendo, J.J. Stoorvogel and Marc Verdegem. Improving the contribution of fishfarming to livelihoods in Northeast Thailand, by Chittra Arjinkit, Roel Bosma, Danai Turongrouang. Benefits of pond-dike systems in Bangladesh, by M.S. Kabir, M.A. Wahab and Marc Verdegem. Common carp increases rohu production in farmers ponds, by Mohammad Mustafizur Rahman, Md. Abdul Wahab and Marc C.J. Verdegem. Improving pond-dike farming systems in the Mekong delta, Vietnam; the Can Tho approach, by Dang Kieu Nhan, Le Thanh Duong, Le Thanh Phong, Roel H. Bosma and Marc C.J. Verdegem. Fuzzy pathways for farm development in Vietnam, by Roel H. Bosma, Le Thanh Phong, and Dang Kieu Nhan
Nitrogen transformations and fluxes in fish ponds: a modelling approach
No full textJiménez-Montealegre, R. (2001). Nitrogen transformations and fluxes in fish ponds: a modelling approach. [Tesis Doctoral].
Wageningen University.Nitrogen is a key element in aquatic environments, and in Aquaculture it is an important pond management variable. In current aquaculture research two important goals are to maintain the water quality within the system, and to improve the retention of nutrients applied to the system in order to minimize the discharge. The principal objectives of this study were to integrate the information available of nitrogen processes in fish ponds into a predictive model, and to investigate further the nitrogen dynamics between the water, the sediments and the biota present in this systems. First, a nitrogen balance in fish ponds was followed along a growing cycle; by combining estimates of the deposition rates of uneaten feed, faeces and dead phytoplankton with measurements of nitrogen accumulation in the sediment, the rate of decomposition of organic matter in the sediment was evaluated. The cumulative recovery at the end of the experiment was almost 100%, meaning that the nitrogen budget in the system studied can be fully explained without any consideration of nitrogen volatilisation, due to either denitrification or ammonia volatilisation. The interactions between various N-species are complex and difficult to integrate. A model that calculates the amounts of various N- compounds in the water column and in the sediment was constructed, and used to gain insight into the relative importance of transformation processes between the various N-compounds. The model was divided into three modules: fish, phytoplankton and sediment-water. All concentrations of the various N-species present were simulated well except the N retained in organic matter in the sediment. To improve our understanding of the bottom organic matter dynamics, and make the model a more comprehensive predictive tool, an estimation of the principal sources of organic matter that accumulate in fish pond bottoms was assessed. Organic matter accumulation in fish ponds was quantified, and the data was used to construct, to calibrate and to validate a dynamic simulation model of organic matter deposition/decomposition in fish ponds. Besides, the rates of sedimentation and resuspension were measured along a growing cycle, following the influence of nutrient input, water parameters, fish biomass and fish size on these processes. Using a dilution analysis method to differentiate between sedimented and resuspended particles, sedimentation and resuspension rates were calculated. The rate of material collected in sediment traps increased from 88.5 to 330 g/m2 per day along the growing cycle, but the relative resuspension did not change significantly, being always in the range of 42 to 47% of the total collected material. The processes of sedimentation of organic matter and resuspension were included in the original model. The proportion of three principal sources of organic matter that accumulate in the pond bottom were also included as parameters of the sedimentation process. A logistic equation relating the rate of resuspension and the fish biomass was calculated; and seepage, as a potential loss of nitrogen from the system, was also considered. The additions to the model represented a substantial improvement to model simulations.El nitrógeno es un elemento clave en los ambientes acuáticos y en la acuicultura es una variable importante en la gestión de estanques. En la investigación acuícola actual, dos objetivos importantes son mantener la calidad del agua dentro del sistema y mejorar la retención de nutrientes aplicados al sistema para minimizar la descarga. Los principales objetivos de este estudio fueron integrar la información disponible de los procesos de nitrógeno en estanques de peces en un modelo predictivo e investigar más a fondo la dinámica del nitrógeno entre el agua, los sedimentos y la biota presente en estos sistemas. Primero, se siguió un balance de nitrógeno en los estanques de peces a lo largo de un ciclo de crecimiento; Mediante la combinación de estimaciones de las tasas de deposición de alimentos no consumidos, heces y fitoplancton muerto con mediciones de la acumulación de nitrógeno en el sedimento, se evaluó la tasa de descomposición de la materia orgánica en el sedimento. La recuperación acumulada al final del experimento fue casi del 100%, lo que significa que el balance de nitrógeno en el sistema estudiado se puede explicar completamente sin considerar la volatilización del nitrógeno, debido a la desnitrificación o la volatilización del amoniaco. Las interacciones entre varias especies N son complejas y difíciles de integrar. Se construyó un modelo que calcula las cantidades de varios compuestos N en la columna de agua y en el sedimento, y se utilizó para comprender la importancia relativa de los procesos de transformación entre los diversos compuestos N. El modelo se dividió en tres módulos: peces, fitoplancton y sedimentos-agua. Todas las concentraciones de las diversas especies de N presentes se simularon bien, excepto el N retenido en la materia orgánica del sedimento. Para mejorar nuestra comprensión de la dinámica de la materia orgánica del fondo y hacer del modelo una herramienta predictiva más completa, se evaluó una estimación de las principales fuentes de materia orgánica que se acumulan en el fondo de los estanques de peces. Se cuantificó la acumulación de materia orgánica en estanques de peces y los datos se utilizaron para construir, calibrar y validar un modelo de simulación dinámica de la deposición / descomposición de materia orgánica en estanques de peces. Además, las tasas de sedimentación y resuspensión se midieron a lo largo de un ciclo de crecimiento, siguiendo la influencia del aporte de nutrientes, los parámetros del agua, la biomasa y el tamaño de los peces en estos procesos. Utilizando un método de análisis de dilución para diferenciar entre partículas sedimentadas y resuspendidas, se calcularon las tasas de sedimentación y resuspensión. La tasa de material recolectado en trampas de sedimentos aumentó de 88.5 a 330 g / m2 por día a lo largo del ciclo de crecimiento, pero la resuspensión relativa no cambió significativamente, estando siempre en el rango de 42 a 47% del material total recolectado. Los procesos de sedimentación de materia orgánica y resuspensión se incluyeron en el modelo original. También se incluyó como parámetros del proceso de sedimentación la proporción de tres fuentes principales de materia orgánica que se acumulan en el fondo del estanque. Se calculó una ecuación logística que relaciona la tasa de resuspensión y la biomasa de peces; y también se consideró la filtración, como una pérdida potencial de nitrógeno del sistema. Las adiciones al modelo representaron una mejora sustancial de las simulaciones del modelo.European Commission under the INCO-DC Programan
Fish Culture and Fisheries Group, Wageningen University and Research Center,
The Netherlands.Universidad Nacional, Costa RicaEscuela de Ciencias Biológica
Organic matter decomposition in simulated aquaculture ponds
No full textDifferent kinds of organic and inorganic compounds (e.g. formulated food, manures, fertilizers) are added to aquaculture ponds to increase fish production. However, a large part of these inputs are not utilized by the fish and are decomposed inside the pond. The microbiological decomposition of the organic matter is a critical factor for water quality control and nutrient recycle. Usually, management practices are developed to control the survival and health of the cultured animals and to maintain good water quality. The microbiological processes are affected by these practices but usually unintentionally. A better control of culture conditions and sustainability of aquaculture ponds is possible with an improvement of the microbiological processes. The present thesis is divided in two parts, the first is a literature review of the microbial ecology of aquaculture ponds and the second is the description of a series of experiments in lab-sc ale aquaculture ponds.In the first part, the role of the microorganisms in aquaculture ponds is reviewed, focusing on the decomposition of organic matter and its influence on pond dynamics. It was theoretically estimated that the addition of I kg of formulated feed would yield approximately 125 g bacterial biomass. This bacterial biomass is potentially a valuable nutrients source for higher trophic levels. Sedimentation and resuspension processes are important factors affecting the decomposition pathways. Both processes are directly related with the feeding rate and the stocking density applied. The rate of organic matter loading, environmental factors and pond management practices influence the functioning of algae-bacteria interactions, which are extremely important in pond processes. Included is a literature that describes commercial probiotic products that claim to solve: nutritious, water quality and pathogens problems in pond aquaculture, were analyzed. Alternative management practices to steer the decomposition process were also presented (Chapter 2).The second part describes all the experiments that were conducted in lab scale microcosm systems, simulating the conditions of an intensive fish-less aquaculture pond with daily feeding rates. In Chapter 3 the influence of aerobic and anaerobic conditions and the organic C/N ratios on the decomposition process is described. Under aerobic decomposition less organic carbon remained in the systems. The results from this experiment suggest that a C/N ratio ranging between the tested values (6.3 and 12.8) does not have a significant influence on the carbon mineralization in the short term " 50 days). However, a C/N ratio decrease was observed in all the treatments during the experimental period; this reduction was especially fast and steep under aerobic conditions. This decrease in C/N ratio of the organic matter might explain why in all treatments the rate of decomposition slowed down at the end of the experiment. The C/N ratio also determined the concentration of inorganic nitrogen compounds in the water. Higher concentrations were found for the richest protein diet treatments. No nitrification was measured even though oxygen and ammonia were present.Bacterial biomass production was quantified testing two formulated fish feed with different protein content under aerobic and anaerobic conditions (Chapter 4). The oxic status significantly influences the bacterial abundance, bacterial biomass, bacterial respiration and bacterial efficiency. More bacterial biomass was produced under aerobic conditions. The two diets did not influence significantly the bacterial growth. The bacterial abundance at the end of the experiment was 3.4 x 109 cells ml-1 in aerobic treatments and 1.9 x 109 cells m1-1 in anaerobic treatments. The remaining amount of carbon, fixed in bacterial biomass and expressed on a per area basis, was 19 g m-2 day-t for aerobic system and 8 g m-2 day-1 for anaerobic systems.In Chapter 5 the effect of the oxic-anoxic range on fish feed decomposition was investigated. Different ranges, from completely aerobic to completely anaerobic, were tested. To establish intermediate oxic levels the following treatments were used: 1) alternated flows of 02 or N2 at different periods and 2) maintaining the coexistence of aerobic and anaerobic layers while applying short resuspension events. Similar amounts of carbon were converted to CO2 under completely aerobic conditions and under the different ranges of aerobic-anaerobic conditions. Under anaerobic conditions much less carbon was converted into CO2. This means that actually only limited periods of oxic conditions (or resuspension) are needed to stimulate complete organic matter decomposition. From our results it appears that only 6h per day of aerobic conditions or only once mixing of aerobic and anaerobic layers (i.e. resuspension) per four days are needed to reach the same carbon mineralization as in continuous aerobic conditions. Very limited nitrification was observed in the completely aerobic treatment. Nitrification and denitrification were registered for all the systems when aerobic and anaerobic conditions coexisted in time or space. The highest nitrogen removal (around 70%) was found in the resuspension treatments (and 12 h O2 flow treatment).The use of controlled lab scale microcosm simulating intensive aquaculture ponds allowed us to follow the fate of carbon and nitrogen during particular decomposition processes. The results found in the different chapters are discussed in Chapter 6. Both the quality and the quantity of the organic matter influenced the decomposition process and its products. The use of high protein diets increased the concentration of nitrogen species affecting the water quality. The aerobic and anaerobic conditions determined the nutrients pathway (mineralized, assimilated or partially decomposed). More bacterial biomass was produced under aerobic conditions than under anaerobic. The coexistence of aerobic and anaerobic conditions stimulated organic matter decomposition; it avoided the accumulation of ammonia while maintaining good water quality conditions.A better understanding and control of the organic matter decomposition in aquaculture ponds is crucial. The anaerobic decomposition only becomes a problem when it predominates in the sediment, causing the aerobic-anaerobic interface to move up into the water column, and thus remains disconnected from the aerobic decomposition. Management practices that link aerobic and anaerobic processes can stimulate fish production by recycling carbon and nitrogen compounds. The recycling of surplus organic matter through bacterial processes, however, has a limit. Increasing fish pond productivity should come along with practices to stimulate the autotrophic and heterotrophic food webs, without exceeding the capacity of this aquatic system
Improving sustainability of striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta, Vietnam through recirculation technology
No full textThe aim of this thesis was to document improvements in sustainability indicators of striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878) production through the application of recirculation and waste treatment techniques. To be able to document improvements in sustainability, in each system studied the same set of twenty sustainability indicators were measured. Indicators related to the use of fingerlings, water, diesel oil, electricity, labor, chemicals and antibiotics. Also, indicators related to nutrient utilization efficiencies and waste discharge were monitored. In addition, a sampling scheme, allowing to calculate organic matter, nitrogen, phosphorous and chemical oxygen demand mass balances covering a full production cycle and applicable in different production systems, was developed. Overall, from a sustainability point of view, striped catfish culture in ponds compared well to other important aquaculture species. Although favorable, it was concluded that water, chemicals and antibiotics use, survival, and the amounts of waste discharged could be further reduced through recirculation and treatment of solid wastes. The realized improvements through RAS technology and waste treatment technology were quantified in lab or pilot scale experiments. Large improvements were realized for water, antibiotic and chemical use, survival, waste discharge and color grade of striped catfish fillets at harvest. In addition, in RAS, utilization efficiencies of nutrients supplied through feeding were improved. Solid wastes removed from ponds or RAS could be partially re-used by making compost or producing methane for generating electricity. Another approach tested was the integration of a denitrification reactor in the recirculation system, which allowed to decompose solid waste and reduce nitrogen discharge. Denitrification in RAS did not affect fish growth, nutrient retention efficiencies and the quality of the fish fillets produced, and thus also improved sustainability of striped catfish farming. In conclusion, application of recirculation and waste treatment techniques tested in this thesis improved the sustainability for striped catfish culture. The challenge remains to scale up RAS and waste treatment technology for striped catfish to the production volumes handled in outdoor ponds without raising production costs.</p
Effect of salinity and feed sterilization in interactions between gut and water microbial communities in Nile tilapia (Oreochromis niloticus) larvae
No full textDissertação de mest., Aquacultura e Pescas, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2010Some tilapia species, including Oreochromis niloticus, are good candidates for brackish water culture due to salinity tolerance and good growth performances. In this report, the effect of salinity on the bacterial dominance in fish gut, as well as their relation with water and feed microbial communities, were tested. The effect of a regular diet versus a sterile diet on the microbial community composition in the fish gut was also evaluated. This resulted in 4 treatments, randomly assigned to 12 aquaria active suspension systems. The experiment was had the duration of 42 days, from the moment of first feeding. The effects of these two factors (salinity (fresh water and salt water) and feed sterilization (non-sterile feed and sterile feed)) on the microbial composition in water and fish guts were evaluated in a 2x2 factorial design. Ten fish guts per aquaria and 1 water sample per aquarium were sampled on days 0, 7, 14, 28 and 42. Bacterial DNA was extracted and amplified by Polymerase Chain Reaction. Bacterial DNA profiles were obtained through Denaturing Gradient Gel Electrophoresis. All the samples were clustered based on band position and intensity (Pearson correlation) and the similarity values among sample profiles were obtained. The gut microbial communities were different between fishes from fresh and salt water systems on day 7 (88.2±9.52% vs 63.7±28.14%) and 28 (76.9±8.28% vs 70.2±17.58%). A significant increase of similarity between system water bacterial communities and fish gut over the different sampling days was observed. Feed also had a significant increase of similarity with fish gut over time, starting with 0.4±10.2% for fresh water and 3.5±2.94% for salt water, and ending with a significantly higher value of 21.7±11.09% for fresh water and 30.4±14.12% for salt water. On the other hand, feed sterilization presented significant differences in all sampling days between fresh and saltwater bacteria populations. However, gut microbiota from fish fed with sterile feed suffered less the effect of water and feed than the fish fed with regular feed. Clearly, this study is a starting point for the complete understanding of how microbial communities are established and what the goals of future research should be.Algumas espécies de Tilápia, como Oreochromis niloticus, são consideradas boas candidatas à cultura em água salobra devido à sua tolerância à salinidade e às suas boas performances de crescimento. Neste relatório, foi testado o efeito da salinidade na dominância bacteriana no intestino de peixe, assim como a sua relação com as comunidades microbiológicas presentes na água e no alimento. O efeito de uma dieta livre de bactérias foi comparado ao de uma dieta regular, com objectivo de verificar a influência da esterilização do alimento nas populações bacterianas no intestino. Para atingir o objectivo principal, foi montado um conjunto de doze tanques de active suspension. A experiência teve a duração de 42 dias. Puderam ser distintos dois factores, salinidade (água doce e salgada) e esterilização de alimento (alimento não-estéril e alimento estéril). Foi amostrada água por aquário, assim como 10 intestinos de peixe por aquário em 5 pontos de amostragem distintos (dia 0, 7, 14, 28 e 42). O DNA bacteriano foi extraído e amplificado por Polymerase Chain Reaction. Os perfis de DNA bacteriano foram obtidos por Denaturing Gradient Gel Electrophoresis. Todas as amostras foram agrupadas com base na intensidade de banda (Pearson correlation) e assim os valores de similaridade entre estes perfis foram obtidos. A dominância bacteriana no intestino de peixe de água doce e salgada é significativamente diferente no ponto de amostragem 7 (88.2±9.52% vs 63.7±28.14%) e 28 (76.9±8.28% vs 70.2±17.58%). Observou-se um aumento significativo de similaridade entre as comunidades bacterianas da água do sistema e os intestinos de peixe, ao longo dos diferentes pontos de amostragem. O alimento também teve um aumento significativo de similaridade com o intestino de peixe ao longo do tempo, começando com 0.4±10.2% para a água doce e 3.5±2.94% para água salgada e acabando com um valor significativamente alto 21.7±11.09% para água doce e 30.4±14.12% para água salgada. Por outro lado, a esterilização de alimento apresentou diferenças significativas em todos os pontos de amostragem, entre populações bacterianas de água doce e salgada. No entanto, a microflora dos peixes alimentados com alimento estéril sofreu um efeito da água reduzido, quando comparado com os peixes alimentados com alimento regular. Claramente, este estudo revela-se um ponto de partida para o conhecimento completo de como as comunidade bacterianas são estabelecidas e quais serão os objectivos para futuras investigaçõe
Food web interactions and nutrients dynamics in polyculture ponds
No full textArtificial feed and fertilizers are the main sources of nutrients supporting fish growth in aquaculture ponds. The majority of the added nutrients are lost to the sediment, where they are no longer available for natural food production. By increasing resuspension of the sediment through the introduction of benthivorous fish, nutrient loss may be reduced, because of the re-mobilisation of nutrients from the sediment. The effects of addition of benthivorous fish and/or artificial feed in fertilized ponds have mostly been studied separately. Therefore, this thesis focuses on the integrated study of the (interacting) effects of the addition of artificial feed and a benthivorous fish species on overall nutrient dynamics, pond ecology, and growth and production of fish in polyculture ponds. To achieve this we used rohu ( Labeo rohitaHamilton) and common carp ( Cyprinus carpio L.), two cyprinid species, because rohu-common carp polyculture is becoming popular practice inBangladesh. Common carp is benthivorous, stirring up bottom sediment, resulting in nutrient resuspension, while rohu is planktivorous and an efficient plankton grazer. Three common carp densities (0, 0.5 and 1 individual m -2 ) were applied with a fixed density of rohu (3 individuals m -2 ) in both artificially fed and unfed ponds. The aim of the study was to quantify the effects of feed and common carp addition and their interactions on water quality, nutrient accumulation, natural food production, behaviour, growth and yield of the fish. Moreover, we tried to find out whether there would be a common carp density that would be optimal for fish production in rohu ponds.The present thesis was divided into three parts. The first part was a literature review on the status of carp polyculture and role of common carp and artificial feed on biotic and abiotic components in ponds or lakes. The second part analyzed changes of various biotic and abiotic parameters and measured synergistic effects triggered by the rohu-common carp combination. The third part monitored changes in swimming and grazing behaviour, and social interactions between rohu and common carp.The first part of this study (Chapter 1) focused on the positive and negative effects of benthivorous fishes on nutrients and natural food availability. Benthivorous fishes stimulated mineralization of organic matter, liberation of nutrients from sediment to the water column and primary production. The density of benthivorous fishes affected turbidity and grazing pressure on natural food, which in turn affected natural food availability. Therefore, the density of benthivorous fishes will affect the overall performance of any polyculture system.Part 2 includes Chapters 2, 3 and 4.àChapter 2, explored the links between water quality parameters, different types of food resources available, fish diet composition and fish growth/production. Common carp increased bioavailable nitrogen and phosphorus, a process that was enhanced by the addition of artificial feed. The effects of common carp were more pronounced in treatments with 0.5 than 1 common carp m -2 . PO 4 -P concentration was strongly correlated with phytoplankton and zooplankton biomass. One of the major findings was that rohu growth was best explained by natural food intake, while common carp growth was best explained by artificial feed addition and negatively correlated with natural food ingestion. Results indicated that common carp benefited directly from artificial feed addition while rohu benefited indirectly from the boost in natural food availability triggered by the fertilizing effect of the artificial feed. àIn Chapter 3, the effects of different densities of common carp (0, 0.5 and 1 individual m -2 ) on natural food availability, natural food ingestion uptake and fish growth were compared under fed and unfed conditions. Stocking 0.5 common carp m -2 resulted in the highest observed natural food availability, the highest natural food ingestion, the highest fish growth (rohu: 1.55% body weight day -1 , common carp: 1.59) and the highest total fish production (3,532 kg ha -1 137 day -1 ). The effects were less pronounced when stocking 1 common carp m -2 . Rohu shifted from phytoplankton to zooplankton when the latter became more available in response to artificial feed addition. àChapter 4 investigated the effects of common carp and artificial feed addition on water quality parameters and on the accumulation of nutrient in different types of natural foods present in the ponds. In all treatments all water quality parameters remained favourable for fish growth. The overall nitrogen and phosphorus concentrations were highest in treatments with 0.5 common carp m -2 followed by treatments with 1 and 0 common carp m -2 , respectively. The oxygen concentration decreased with increasing common carp density. More nitrogen and phosphorus accumulated in fish, phytoplankton and zooplankton in treatments with 0.5 common carp m -2 , followed by treatments with 1 and 0 common carp m -2 , respectively. The nitrogen and phosphorus accumulation in sediment was lower in presence of common carp than in the common carp free treatments. Concentrations of all nitrogenous and phosphorus compounds were higher in fed than in non-fed ponds except for NO 2 -N. A larger fraction of the input nutrients accumulated in all natural food types in non-fed than fed pond whereas the opposite were observed for the fraction of nutrients accumulating in the sediment. · In the third part of this study (Chapter 5) the resting, grazing, swimming and social interactions of rohu and common carp were observed in purpose build tanks for the same treatments as applied in part 2. Rohu decreased intra-species and increased inter-species interactions with increasing common carp density. Presence of common carp reduced the resting time and increased swimming and grazing time of rohu near the tanks bottom. Rohu benefited from spending more time close to the bottom and wall in presence of common carp by ingesting more zooplankton, as in these areas zooplankton biomass was higher than in other parts of the tanks.A general discussion of the experimental results is given in Chapter 6. Both addition of common carp and artificial feed affected the pond ecology, fish growth, total production and fish behaviour. Stocking 0.5 common carp m -2 was better than stocking 1 m -2 . The strength of this study is that it looked at the combined effects of stocking benthivorous fishes and feed addition considering water quality, natural food availability, feed intake and behaviour. Results show that behavioural observations are equally important as water quality and feed intake monitoring to explain synergism in polyculture. Similar studies, adding a third species, are recommended to further elucidate changes in the food web dynamics when synergism is observed in polyculture ponds
The role of a fish pond in optimizing nutrient flows in integrated agriculture-aquaculture farming systems
No full textIn the Mekong delta, the Vietnamese government promoted integrated agriculture-aquaculture (IAA) farming systems as an example of sustainable agriculture. An important advantage of IAA-farming is the nutrient linkage between the pond and terrestrial components within a farm, which allows to improve resource use efficiency and income while reducing environmental impacts. This study monitored and analyzed water use in and nutrient flows through ponds that are part of an IAA-farming system. The goal was to improve the nutrient management of ponds which in turn lead to improved water and nutrient use efficiency of the whole IAA-farm. The study included three main parts: (1) understanding the context and characteristics of IAA-systems (chapters 2 and 3), (2) analyzing the performance of IAA-systems, suggesting and testing improvements (chapters 4 and 5), and (3) recommending procedures for the continuous upgrading of existing IAA-farming systems (chapter 6). The research was done on-farm in freshwater areas of the Mekong delta and followed a Participatory Learning in Action approach. Different multivariate statistical methods were applied for data analysis. At community and household level, results showed that the type of IAA-farming systems applied was determined by a mixture of bio-physical, technological and socio-economic factors (chapter 2). Three major IAA-systems were identified: (1) low-input fish farming in fruit-dominated area (system 1), (2) medium-input fish farming (system 2), and (3) high-input fish farming (system 3) in rice-dominated areas. System 1 was commonly practiced in a rural and intensive fruit production area with fertile soils, while systems 2 and 3 were more frequent in peri-urban and in rice production areas with less fertile soils. In the study areas, poor farmers usually did not adopt IAA-farming. With good market accessibility, richer farmers tended to intensify fish farming. The principal factors why farmers did not start aquaculture were the inappropriateness of the technology available, lack of capital, insufficient land holding, poor access to extension services, limited farm management, and a fear of conflicts associated with pesticide use on crops. The main motivations to practice IAA-farming were increased farm resource uses, which resulted in improved income, a better supply of foods for home consumption and a reduction of the environmental impacts from the farming. In low- and medium-input ponds, nutrient inputs, the accumulation of nitrogen (N), organic carbon (OC) and phosphorus (P) and environmental impacts were closely linked (chapter 3). Parameters related to nutrients input levels and water exchange rates in ponds explained most of the variability between farms. Parameters linked to agro-ecological sites, pond physical properties and livestock or human excreta inputs explained most of the remaining variability. A combination of these variables allowed to characterize three indicative integrated systems: (1) the low water-exchange-rate ponds in the fruit-dominated area, (2) the low water-exchange-rate ponds in the rice-dominated area receiving home-made feed, and (3) the high water-exchange-rate ponds in the rice-dominated areas receiving excreta. These systems concurred to a large extend with the systems identified on the basic of the community and household survey. In the rice-dominated area with deep ponds, more livestock or human wastes were supplied, and high water exchange rates were practiced. In these ponds, large excreta-OC loads reduced dissolved oxygen and increased total phosphorus concentrations in the water column and nitrogen, organic carbon and phosphorus accumulation in the sediments. In the rice-dominated area with wide ponds, more home-made feed was applied and low water-exchange rates were practiced, which resulted in a high phytoplankton biomass and primary productivity. On the contrary, in the fruit-dominated area fish were grown in shallow and narrow ditches with a low phytoplankton biomass and only a small fraction of the nutrient input accumulated in the sediments. The water and nutrient budgets of a selected number of ponds, representing either low or high water-exchange systems were determined (chapter 4). The sluice-gate water inflow and outflow largely dominated the total pond water budgets, accounting for 72-97% of the total water budget. On-farm livestock manures were the most important nutrient source for ponds. High water-exchange rate ponds received larger quantities of livestock and/or human excreta and had significantly higher volumes of water passing through ponds than low water-exchange rate ones. Only 5-6% of the total N, OC and P inputs were retained in the harvested fish, but 18-91% accumulated in the pond sediments, the rest was lost through pond water discharges. Fish yields and the quantity of nutrients accumulating in the sediments increased with increasing on-farm nutrient input levels at the cost of higher nutrient discharges. Its was concluded that farmers need to manage water and nutrient flows between the pond and the other IAA-farm components with the goals to maximize productivity and profitability while minimizing nutrient discharges of the farm as a whole. Excreta were the principle type of nutrient input applied to ponds in the study areas. Therefore, the economic and nutrient discharge tradeoffs stemming from the use of livestock and human excreta were analyzed (chapter 5). Data collected during three consecutive production years were combined in the analysis. Results showed that increased excreta input levels resulted in lower dissolved oxygen concentrations, higher water exchange rates practiced, and increased discharge of chemical oxygen demand (COD), N, P and total suspended solids (TSS). Fish yields and the accumulation of N, OC and P in pond sediments, however, increased with increasing excreta input levels. Through regression analysis, it was predicted that with an input of 5 kg N ha-1 day-1, a fish yield of 8379 kg and an economic return of 52 million VND ha-1 yr-1 will be obtained while about 2057 kg COD, 645 kg N, 213 kg P and 39203 kg TSS ha-1 yr-1 will be discharged from the farm. At this input level, about 9% of input-N will be retained in harvested fish, 52% will accumulate in the sediments and 39% will be discharged. Further development of IAA-farming practices should focus on reducing nutrient discharges while maintaining favorable economic returns. In brief, this study demonstrated that the adoption of one type of IAA-system by farmers is determined by a mixture of factors at different scales ranging from the individual pond to community or village level. Within each IAA-system, the pond fulfils multiple roles, in part influenced by the existing resource base, agricultural development pathways and the household's goals and aspirations. An important function of ponds is the trapping and storage of nutrients for subsequent reuse within IAA-systems, which otherwise would be lost. Optimizing nutrient storage in ponds also concurs with best management practices from an environmental and economic point of view. The key challenge to the further development and optimization if IAA-farming is to balance economic, environmental and social interests within a highly dynamic setting of the Mekong delta today
On the role of the polychaete Dendronereis spp. i the transmission of white spot syndrome virus in shrimp ponds
No full textWhite spot syndrome virus (WSSV) is by far the most devastating shrimp virus. Control measures have lowered the WSSV incidence to various degrees, but the pathogen remains plaguing shrimp culture worldwide. Continuous exposure may cause WSSV to adapt and infect non-crustacean benthic fauna in ponds such as polychaetes, hence, extending WSSV host range to maintain virus persistence in ponds. Dendronereis spp. (Pieters 1854) are ubiquitous Nereid polychaetes in shrimp ponds in Indonesia and part of the shrimp’s natural diet. This thesis aimed to investigate the possible role of Dendronereis spp. in the transmission of WSSV in shrimp ponds. The significance of the findings may provide new insight on the persistence of WSSV in the pond environment and novel strategies for disease management. The investigation started with a survey to determine the occurrence of WSSV in Dendronereis spp. in Indonesia, followed by subsequent laboratory observations to determine the role of Dendronereis spp. in white spot syndrome disease development. Field surveys in selected ponds in two research locations in Indonesia, the Mahakam delta (East Kalimantan) and the vicinity of Semarang (Central Java), showed that WSSV infection in Dendronereis spp. is quite common. Point prevalence of WSSV infected Dendronereis spp. was 44 ± 27% (± SD). The average prevalence in Mahakam delta was 73 ± 22% and in Java 26 ± 38%. This result implied that WSSV-infected Dendronereis spp. are widely distributed. WSSV replicated in the gut of naturally-infected Dendronereis spp. as detected in cell nuclei via immunohistochemistry (IHC) using monoclonal antibodies and via RT-PCR to detect the viral mRNA. These experiments showed that Dendronereis spp. are natural and susceptible hosts of WSSV. WSSV was transmitted from naturally infected Dendronereis spp. to Litopenaeus vannamei (Boone 1931) through the oral route and further to new naïve shrimp showing natural transmission of WSSV from polychaetes to shrimp. This indicates that the transmission of WSSV from polycheates to shrimp is possible. An experiment using Hediste diversicolor (O.F. Müller 1776) as a more amenable alternative model animal to study WSSV infection in polychaetes showed that this polychaete was not susceptible to WSSV infection using methods commonly used to induce infection in shrimp. In ponds, WSSV infection incidence in Dendronereis spp. correlated positively with Dendronereis spp. density and with the proportion of WSSV infection in shrimp. Findings of the present study underscore that Dendronereis spp., as ubiquitous and resident animals in the shrimp ponds can be reservoir hosts of WSSV and responsible for disease transmission. However, further studies are needed to obtain a better understanding of the importance of Dendronereis spp in WSSV epidemiology in and beyond shrimp ponds. </p
- …
