Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Balancing options for shrimp farming : a landscape approach to investigate the future of shrimp farming in the Mekong Delta
    Joffre, O.M. - \ 2015
    Wageningen University. Promotor(en): Johan Verreth; Arnold Bregt, co-promotor(en): Roel Bosma. - Wageningen : Wageningen University - ISBN 9789462574984 - 196
    garnalenteelt - schaal- en schelpdierenteelt - kustgebieden - milieueffect - landschap - aquacultuur - mangroves - middelen van bestaan - hulpbronnengebruik - geïntegreerde systemen - duurzaamheid (sustainability) - mekong - delta's - shrimp culture - shellfish culture - coastal areas - environmental impact - landscape - aquaculture - mangroves - livelihoods - resource utilization - integrated systems - sustainability - mekong river - deltas

    Balancing options for shrimp farming

    A landscape approach to investigate the future of shrimp farming in the Mekong Delta

    Olivier Joffre

    While providing an option for development in coastal areas, shrimp farming is usually associated with high environmental cost due to the loss of mangrove forest and high social cost as farmers suffer heavy financial losses due to disease outbreaks. Planning shrimp farming requires to integrate risk as well as social and environmental cost. This thesis, using the Mekong Delta as a case, presents an approach to investigate, with local stakeholders, options to plan a resilient and sustainable shrimp farming sector. First, Olivier Joffre analyzed the different shrimp production systems from economic point of view before analyzing farmer’s strategies and providing insights on drivers that will push or, at the opposite, constraint farmers to choose integrated mangrove shrimp systems. This knowledge was integrated in an Agent Based Model (ABM) that was calibrated using Role Playing Games (RPG).

    The effect of future scenarios and different policies on the farmers’ decisions was tested using a combination of RPG and ABM. For one coastal district of the Mekong Delta, the results showed that promotion of intensification of shrimp production has a high social cost and decreases the total production in the study area after 10 years. Policies for supporting the spread of integrated mangrove-shrimp systems, such as Payment for Ecosystem Services, or access to an organic value chain, are not strong enough to influence farmers’ decision toward adopting these systems. Without any adaptation to climate change a sharp decrease of the production is expected. The approach brought local farmers’ knowledge to the attention of decision makers.

    On the role of the polychaete Dendronereis spp. i the transmission of white spot syndrome virus in shrimp ponds
    Desrina, Haryadi - \ 2014
    Wageningen University. Promotor(en): Johan Verreth; Just Vlak, co-promotor(en): Marc Verdegem. - Wageningen : Wageningen University - ISBN 9789462570856 - 181
    polychaeta - witte-vlekken-syndroom-virus - garnalen - ziekteoverdracht - visvijvers - garnalenteelt - voer - reservoir hosts - aquacultuur - polychaeta - white spot syndrome virus - shrimps - disease transmission - fish ponds - shrimp culture - feeds - reservoir hosts - aquaculture

    White 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.

    Global and local governance of shrimp farming in the Mekong Delta, Vietnam
    Tran Thi Thu, H. - \ 2012
    Wageningen University. Promotor(en): Arthur Mol; Han van Dijk, co-promotor(en): Simon Bush. - S.l. : s.n. - ISBN 9789461733764 - 181
    garnalen - garnalenteelt - governance - beleid - aquacultuur en milieu - markten - biologische landbouw - mangroves - vietnam - shrimps - shrimp culture - governance - policy - aquaculture and environment - markets - organic farming - mangroves - vietnam

    The Mekong Delta is one of seven ecological regions in Vietnam where aquaculture and shrimp products are internationally traded and the shrimp farmers are firmly embedded in a global system of production and trade. The growth of shrimp aquaculture, in addition to population growth and higher levels of investment, has left coastal resources in the Mekong Delta increasingly vulnerable to rapid changes in land and resource use. The shrimp industry, made up of multiple stakeholders and fragmented market chains, is also now subject to a range of attempts to govern sustainable and/or responsible shrimp aquaculture. While striving for improved environmental performance to reduce bio-physical variability in production these governance systems have also brought stringent requirements for producers that determine their ability to access international markets. The general objective of the research is to investigate the interactions between existing state and non-state actors and institutions to develop a more informed understanding of how state, market and community-based governance arrangements at different levels influence decision-making in shrimp aquaculture in coastal areas of the Mekong Delta of Vietnam. The general research question explores how different material conditions and social relations affect the effectiveness and responsiveness of governance arrangements aimed at achieving multiple goals of maintaining rural livelihoods, environmental sustainability and improved food quality.

    The first empirical chapter highlights two key transformations of Vietnamese shrimp aquaculture policy in Ca Mau province. The first transformation is an internal policy shift from quantitative to qualitative state-led production goals. The secondtransformation is in response to market demands, but is directed to the emergent ‘quality’ concerns about the environmental and social impacts of tropical shrimp farming. Together these two transformations present a complex balancing act between externally-led global market demands and consumer concerns for the improved environmental and social performance of tropical shrimp production, and the government’s interests in maintaining sovereign control over the shrimp industry. The results also show that the Vietnamese government should continue to position itself as a facilitator of global private governance arrangements, especially as farmers and global market actors are engaged in transnational regulatory networks operationalised at local scales. Moreover, the state needs to give far more attention to market incentives for fostering the participation and compliance of farmers in these transnational regulatory networks.

    The second chapter analyses the case of Naturland organic certification and its implementation in meeting the government’s plan to create an organic coast scaling up the organic farming along southern part of Ca Mau by 2015. Our results support the claim that organic certification can provide a means of linking farm-level management to the sustainability of landscapes dominated by the shrimp-forest integrated farming system in Ca Mau. But this is only achievable if certain challenges are overcome. The first challenge is the tension between farmer practices and externally defined and regulated quality standards.The secondchallenge is to ensure that economic benefit are shared between actors in the organic certified value chain. Finally, the level of legitimacy given to private sector led auditing systems needs to be addressed.

    The thesis then explores the development of shrimp farmer cooperatives and clusters by the government based on a policy to explicitly to increase the competitiveness of the sector in the international market and to improve economic condition for small producers. The results shows that vertical contractualisation under the form of contract farming between farmer cluster with up and downstream chain actors demonstrate economic benefits to small-holder producers engaged in intensive production.The improved extensive system, however, gives further impetus to determining how cooperative forms of production might assist small holders to complying with production-oriented quality standards, which in turn may also improving market performance. The cases therefore supports the claim that the development of shrimp farmer clusters should not solely focus on increasing production efficiency but also successful integration into the value chain; producing high-quality and safe products, and engaging in sustainable on-farm management practices.

    The final case study looks at shrimp farming in the broader context of promoting ecological function in forested shrimp-mangrove farming systems. Attention is given to how incentives are generated for shrimp farmers to plant and protect mangroves by analysing farmer’s decision-making and their perspective on mangroves in relation with state-based governance arrangements, the forest allocation and benefit sharing policies. The results show that farmer’s perception on the role and value of mangroves are positive and they are willing to plant and to protect mangroves both for economic and environmental reasons. Moreover, they want to have control over mangroves although forests are still under the state regulation. However, farmer’s decision-making is very much influenced by the way in which the forest benefit sharing policy is implemented by the state-led forest management boards and forestry companies. The results show that the perception of shrimp farming as the main cause of deforestation and degradation should be reevaluated in the context of integrated shrimp mangrove model because farmers income is improved if mangroves are a part of the production system. Instead the evidence shows that shrimp farmers are potentially the best stakeholders to plant, protect and manage mangroves if they have full rights and responsibilities over forests. Seen as such, shrimp farming is a mangrove-friendly source of revenue which also promotes the planting and protection of mangroves.

    The relation between farming practices, ecosystem, and white spot in syndrome virus (WSSV) disease outbreaks in penaeus monodon farms in the Philippines
    Tendencia Alapide, E. - \ 2012
    Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Roel Bosma; J.H. Primavera. - S.l. : s.n. - ISBN 9789461733702 - 135
    garnalen - witte-vlekken-syndroom-virus - garnalenteelt - uitbraken (ziekten) - epidemiologie - infectieziekten - dierziektepreventie - aquatische ecosystemen - fysicochemische eigenschappen - mangroves - filippijnen - shrimps - white spot syndrome virus - shrimp culture - outbreaks - epidemiology - infectious diseases - animal disease prevention - aquatic ecosystems - physicochemical properties - mangroves - philippines

    The white spot syndrome virus (WSSV) affecting shrimp aquaculture in most producing countries has caused huge economic losses resulting in bankruptcy to both large and small farmers. Studies done on WSSV epidemiology were mostly tank-based and on species other than Penaeus monodon. There is a need to investigate WSSV epidemiology in P. monodon in on-farm situations, thus including both risk and protective factors. This thesis aimed to generate knowledge that can improve prevention against WSSV in shrimp culture through better farm husbandry by studying the epidemiology of WSSV in on-farm situations. To achieve this goal data from cross-sectional and case studies were analysed to identify on-farm WSSV risk and protective factors, and longitudinal studies were done to assess factors affecting water quality and causing WSSV infection to result in an outbreak.

    The thesis identified the following WSSV risk factors related to the physico-chemical parameters of the water: low and fluctuating temperature, low and fluctuating salinity, and pH fluctuation. The risk of high temperature and high salinity for an outbreak of WSV disease may be related to fluctuations in these two parameters. Risk factors related to farm husbandry techniques were feeding with molluscs, sludge removal and its deposition on the dike, sharing water source with other farms and having the same receiving and intake water. Identified WSSV protective factors were high mangrove to pond area ratio, feeding with natural food or phytoplankton, and higher percentage of beneficial bacteria like the yellow colonies that grow on thiosulphate citrate bilesalt sucrose agar, a Vibrio selective medium.

    Results of the longitudinal studies demonstrated that WSSV infection may not result in outbreaks in greenwater pond and in ponds with mangroves in the receiving environment. Our results did not provide explanations why the WSSV infection did not result in an outbreak in farms with mangroves in the receiving environment. In greenwater ponds, this was attributed to the better water and soil quality, higher plankton count, and higher heterotrophic bacterial count.

    Resilience and livelihood dynamics of shrimp farmers and fishers in the Mekong Delta, Vietnam
    Tran Thi Phung, H. - \ 2012
    Wageningen University. Promotor(en): Leontine Visser; Han van Dijk, co-promotor(en): L. XuanSinh. - S.l. : s.n. - ISBN 9789461732170 - 200
    strategieën voor levensonderhoud - middelen van bestaan - garnalenteelt - sociale aanpassing - sociale verandering - vietnam - zuidoost-azië - azië - garnalen - vissers - ontwikkelingslanden - livelihood strategies - livelihoods - shrimp culture - social adjustment - social change - vietnam - south east asia - asia - shrimps - fishermen - developing countries

    Shrimp aquaculture and fishery, the two important economic sectors in Vietnam, have been promoted by the government to reduce poverty, provide job opportunities, and to increase exports to support economic development. However, this expansion of fishery and aquaculture has also had negative effects. Hundreds of thousands of hectares of mangrove forest have been replaced by shrimp ponds and, as a result, have brought ecological risks like water pollution, causing shrimp disease outbreaks. These consequences have negatively affected the sustainability of the livelihoods of millions of coastal people who are dependent on shrimp aquaculture, mangrove forests and fishing.

    As a part of the RESCOPAR program of “Rebuilding resilience in coastal populations and aquatic resources” of Wageningen University (INREF), this study was conducted across four shrimp farming systems and one fishery system in two provinces of the Mekong Delta of Vietnam with a focus the different livelihoods.. The study investigates the pathways and decision-making of shrimp farmers and fishers to cope with risks and uncertainties to sustain livelihoods and enhance socio-ecological resilience.

    Results show that farmers in these systems exhibit remarkable social and economic resilience at household level under declining ecological conditions, particularly mangrove decline, shrimp diseases, market price fluctuations, and misguided government policies and programs. They cope with these vulnerabilities through a wide range of livelihood pathways and strategies including intensification, diversification, migration, specification, and collaboration. The pathways they decide upon at one stage do not only influence the livelihood activities in a particular environment, but they also nurture the process of learning to adapt to the changes, to self-organize and manage their lives for long-term resilience building.

    This study used four indicators as proxies of social resilience: economic stability, resource protection, knowledge building and the creation of relationships.. Between the two improved extensive shrimp farming systems, the extensive mangrove-shrimp system showed more social resilience and was less risky. Moreover, the system was more resilient ecologically, as it did not put environmental pressure on the mangrove forest It needed to conserve part of the mangrove forest that would serve as a nursery ground for marine shrimp and fish species. Between the two intensive farming systems, the intensive farming system where farmers chose to cluster their ponds appeared to have greater social resilience. Farmers in this system were better off, experienced a higher net return/cost ratio, and fewer farms failed due to shrimp diseases. They could also apply to advanced bio-farming technology for shrimp farming. They would build relationships with external agencies for support and they were more active, flexible, and professional in their adaptation. They were able to direct and shape the changes in order to acquire a stronger legal and equity position, thus increasing their social resilience. Small-scale fishery was less socially and ecologically resilient, so fishers diversified their gear and boats to fish more intensively to secure livelihoods and reduce vulnerability. However, this caused near- shore resource decline and ecological disturbance, and violated fishery regulations.

    The Vietnamese Government has established a political and institutional system to support aquaculture and fishery. However, the implementation of the current policies and institutions in the field of aquaculture and fisheries is still weak and inadequate. The institutional interventions, firstly, need to focus on balancing between household economic improvement and natural resources conservation. It is not enough to emphasize only the government’s capacities of control and enforcement to make farmers and fishers comply with the regulations for the conservation of the resources without also emphasizing the need to promote socio- economic improvement at household level. The solution could be to enhance non-farm or non- fishing livelihood diversification, improve pond farming and fishing technologies and to promote farmers collaboration and shrimp certification. Finally, the most important is to devolve the responsibilities and rights for the management of the mangrove forests and the coastal inshore resources to local individual farmers and communities.

    White spot syndrome virus molecular epidemiology: relation with shrimp farming and disease outbreaks
    Tran Thi Tuyet, H. - \ 2012
    Wageningen University. Promotor(en): Just Vlak; Mart de Jong, co-promotor(en): N.T. Phuong; Mark Zwart. - S.l. : s.n. - ISBN 9789461732125 - 136
    moleculaire epidemiologie - garnalenteelt - garnalen - witte-vlekken-syndroom-virus - virusziekten - molecular epidemiology - shrimp culture - shrimps - white spot syndrome virus - viral diseases

    White spot syndrome virus (WSSV), the causative agent of white spot disease (WSD), has been responsible for most shrimp production losses around the world since the early 1990s. Previous research has focused mainly on the characterization of WSSV genomic variation to gain a better insight in the evolution and spread of the virus at the regional and global levels.Although WSSV genetic variation at small spatial scales has been described, the question is whether there is a correlation between this genomic variation and shrimp farming practices and disease outbreak at the local and farm level. Therefore, the present research has been carried out to describe in detail WSSV genetic variation over space and time and to estimate transmission routesof WSSV genotypes in ponds with different farming regimens. Different molecular markers, natural variation contained within the WSSV genome, were tested to quantify these relationships in semi-intensive, extensive and rice-shrimp farming systems within the Ca Mau and Bac Lieu provinces, both in the Mekong Delta, Vietnam. The outcomes of the research showed that (i) there are differences in genetic structure of WSSV populations in shrimp culture areas, with more variation found in variable number tandem repeat (VNTR) regions, short adjoining repeat sequences, than in genomic regions in which large deletions occur; (ii) a correlation betweenWSSV population structure, disease outbreak status and pond farming system was observed, providing evidence that the WSSV VNTR structure (in particular the number of repeat units in ORF94) statistically correlate with disease outbreaks and to a lesser extent to farming system; (iii) mixed-genotype WSSV infections of shrimp are correlated with fewer disease outbreaks in ponds; and (iv) it might be possible to use molecular markers (ORF94 and ORF125) to predict the outcome of WSSV infections in shrimp ponds in the future. For field applications, these findings provide important information for the development of specific management strategies to control WSD.

    Mitigating water pollution in Vietnamese aquaculture production and processing industry : the case of pangasius and shrimp
    Pham Thi Ahn, - \ 2010
    Wageningen University. Promotor(en): Arthur Mol; Carolien Kroeze, co-promotor(en): Simon Bush. - [S.l. : S.n. - ISBN 9789085857723 - 193
    garnalenteelt - visteelt - aquacultuur - waterverontreiniging - voedselverwerking - voedselindustrie - vietnam - aquacultuur en milieu - shrimp culture - fish culture - aquaculture - water pollution - food processing - food industry - vietnam - aquaculture and environment
    Needs assessment traceability for aquaculture shrimp and workshop in Java Timur, Indonesia, 14-18 June, 2010 Java Timnur Indonesia
    Roest, J.G. van der; Lehr, H. ; Yong, A. - \ 2010
    Wageningen : RIKILT - 31
    naspeurbaarheid - voedselveiligheid - aquacultuurtechnieken - garnalenteelt - ketenmanagement - traceability - food safety - aquaculture techniques - shrimp culture - supply chain management
    On the epidemiology and evolution of white spot syndrome virus of shrimp
    Bui Thi Minh Dieu, - \ 2010
    Wageningen University. Promotor(en): Just Vlak, co-promotor(en): Mark Zwart. - [S.l. : S.n. - ISBN 9789085705642 - 135
    garnalen - virusziekten - moleculaire epidemiologie - genetische variatie - virologie - epidemiologie - garnalenteelt - aquacultuur - witte-vlekken-syndroom-virus - moleculaire merkers - shrimps - viral diseases - molecular epidemiology - genetic variation - virology - epidemiology - shrimp culture - aquaculture - white spot syndrome virus - molecular markers
    WSSV causes a devastating disease in shrimp aquaculture that has spread worldwide and probably increased in virulence over time. Understanding WSSV epidemiology and evolution is therefore important for developing novel intervention and management strategies. Both of these goals require finding suitable molecular markers to identify and discriminate WSSV strains, and hereby help infer their origin and track their spread. Five major variable WSSV genomic loci were evaluated as markers for virus identification and virus spread on different spatiotemporal scales. In this thesis the genetic variation between WSSV isolates from the key shrimp production regions in Vietnam was analyzed. A statistically supported model of spread suggests that multiple introductions of WSSV occurred in central Vietnam, and that the virus radiated out over time to the south and the north. Spurious variation was generated during molecular cloning of WSSV VNTR sequences, while no variation occurred in multiple replicates of PCR amplification of VNTRs. Moreover, VNTR sequences were stable over two passages of infection in vivo, indicating that in vivo cloning can be applied to study heterogeneity within WSSV isolates originating from a single shrimp. Genetic deletion of variable region variants appear to be more stable in extensive farms compare to intensive farms over time, indicating that farm practices affect the evolutionary dynamics of WSSV. Genetic variation between Asian WSSV isolates provides support for evolution of genome size according to a geometric model of adaptation, where incrementally smaller genomic deletions are substituted over time. The relationship between the molecular data and the time of first disease occurrence implies that shrimp transportation played an important role in the quick, long range spread of WSSV. Overall, the thesis results show that WSSV variable loci can be effectively employed as molecular markers to study WSSV spread and evolution on different spatiotemporal scales. However, the markers have different properties and the choice of a suitable marker for a pertinent question is critical.


    Identification of specific demands on Feed in Dutch Organic Aquaculture
    Poelman, M. - \ 2009
    Yerseke : IMARES (Rapport / Wageningen IMARES C070/09) - 19
    biologische landbouw - aquacultuur - visvoeding - biologische productie - certificering - garnalenteelt - visteelt - vitaminen - dierenwelzijn - organic farming - aquaculture - fish feeding - biological production - certification - shrimp culture - fish culture - vitamins - animal welfare
    The evaluation of specific demands for organic feed focussed on feed demands for four fish species which can be cultured in Recirculation Aquaculture Systems (RAS), tilapia, African Catfish, shrimp and turbot. The evaluation of the various feed formulations indicates that there are several ingredients, which are common for the four species, and will therefore be used for further elaboration on the organic availability. These feed ingredients, are: fishmeal and oil, corn meal, wheat meal, blood meal, vitamin mix, mineral mix, and antioxidants. Besides the evaluation of the feed ingredients an inventory was made on the demands set by three key organic standards and legislation documents; European legislation (in prep), IFOAM and Naturland. A draft consensus standard containing a synthesis of all demands has been described. The implication of the demands, and the possibilities and bottlenecks for organic feed production were evaluated for the selected feed ingredients. It was concluded that organic feed production for RAS can meet the general criteria set for feed, on GMO material and organic composition. However, for the production of organic feed, a bottleneck will be the necessary requirement of synthetic amino acids for health improvement. The lack of these amino acids in organic feed can result in potential disadvantage for animal needs. This raw material restrictions will most likely also result in the lack of possibilities for fine tuning the feed for animal needs
    'World Aquaculture Society' congres in Zuid Korea: een terugblik
    Verdegem, M.C.J. - \ 2008
    Aquacultuur 23 (2008)3. - ISSN 1382-2764 - p. 19 - 22.
    aquacultuur - republiek korea - garnalenteelt - garnalen - aquaculture - korea republic - shrimp culture - shrimps
    Zuid Korea is een idyllisch lappendeken van dicht bevolkte valleien tussen ongerepte beboste heuvels omkranst door prachtige kusten. Niets lijkt er oud, zelfs de weinig historische gebouwen zijn er keurig opgeknapt. Jong of oud werkt er gemiddeld 11-12 uur per dag en vindt 5 betaalde verlofdagen per jaar voldoende. Gelukkig zijn er ook veel officieel vrije dagen. Een impressie van het congres op van 19 tot 23 mei 2008 gehouden werd in Busan, Zuid-Korea
    Inventory of possible emerging hazards to food safety and an analysis of critical factors
    Kleter, G.A. ; Poelman, M. ; Groot, M.J. ; Marvin, H.J.P. - \ 2006
    Wageningen : RIKILT (Rapport / RIKILT 2006.010) - 41
    voedselveiligheid - gevaren - risicoschatting - antibiotica - antibioticumresiduen - garnalen - garnalenteelt - plantaardige pesticiden - food safety - hazards - risk assessment - antibiotics - antibiotic residues - shrimps - shrimp culture - botanical pesticides
    Various recent incidents around food safety issues have led to the establishment of the European Food Safety Authority and its national counterparts in the member states of the European Union. Besides these measures, it is desirable to identify food risks while they are still emerging, i.e. when they still are hazards.
    Penaeus monodon post-larvae and their interaction with Rhizophora apiculata
    Nga, B.T. - \ 2004
    Wageningen University. Promotor(en): Marten Scheffer, co-promotor(en): Rudi Roijackers. - Wageningen : WUR - ISBN 9789085040934 - 111
    penaeus monodon - garnalen - rhizophora apiculata - mangroves - interacties - aquacultuur - garnalenteelt - schaal- en schelpdierenvisserij - populatiedynamica - mortaliteit - ligstro - voedingsstoffen - toxiciteit - vietnam - penaeus monodon - shrimps - rhizophora apiculata - mangroves - interactions - aquaculture - shrimp culture - shellfish fisheries - population dynamics - mortality - litter - nutrients - toxicity - vietnam
    In recent years, expansion of shrimp aquaculture in Vietnam has brought considerable financial benefits to farmers and local communities. In the coastal provinces in the Mekong Delta, brackish shrimp aquaculture is the major economy activity. Extensive shrimp-mangrove culture systems are popularly practiced here. Although the average shrimp production is low, due to over-exploitation and destruction of mangrove forests and salt marshes, these systems are of special interest in view of the problems of sustainability of intensive aquaculture (Naylor et al. 2000 Nature 405: 1017-1024). Several studies demonstrated that mangrove swamps are highly productive ecosystems providing food, shelter and nurseries for various aquatic organisms, many of which are commercially important. The tiger shrimp, Penaeus monodon , is a clear example in this case. Natural shrimp production in these areas is believed to depend to a large extend on the presence of mangroves. However, the complex of mechanisms through which mangroves affect shrimp production is still poorly understood. The work in this thesis is an attempt to unravel some of the key-processes involved. It confirms the picture that mangrove litter represents a formidable input of organic material and nutrients into the aquatic system, and reveals how this input may have positive as well as negative effects on growth and survival of post-larval shrimp.

    Mangrove stands of different age have been studied for one year with respect to their litter fall and nutrient input (chapter 2). Litter fall consisted for 70% of leaf litter and organic matter accounted for 90% of the dry weight. Litter fall declined with the age of the mangrove stands, and also nitrogen and phosphorus levels were considerably higher in the leaf litter of younger stands (7 and 11 years) as compared to the older stands (up to 24 years). Thus, both the amount and the quality of litter input to the aquatic systems are highest in younger mangrove stands.

    As a next step key factors affecting the decomposition of mangrove leaves were analyzed (chapter 3). Decomposition rates tended to be highest at lower salinities, and reached an optimum at 5 ‰. The decomposition rates were also highest in the wet season, and this may well be due torelatively low salinities in this period. Wet season salinity in the Camau area was in the range of 4 - 9 ‰, close to the optimum for decomposition derived from laboratory experiments. Our studies also indicated an effect of humidity per se. We found that the decomposition rate was higher for leaves submerged in the ditches, than for leaves incubated near the roots of mangrove stands in the open air, where decomposition rates were higher in the wet than in the dry season. We also analyzed the dynamics of nutrient concentrations in decomposing litter. Nitrogen and phosphorus levels in decomposing leaves increased during the decomposition period. This enrichment indicates an increase of food quality over the first period of decomposition .

    The following chapters show that the effects of decomposing mangrove leaves on shrimps can be positive but also negative (Chapter 4 and 5). The amount of decomposing leaves appeared key. At high concentrations of leaves negative effects prevailed. These effects were probably due tothe release of nitrite and sulphide, and a decrease in dissolved oxygen concentration. On the positive side, mangrove moderate concentrations of leaves promoted growth of Penaeus monodon post-larvae, and apparently served as a shelter and as a food source.The fact that micro-organisms growing on the leaves, rather than the leaf material itself may be important as food was illustrated by the result that shrimps feeding on mangrove leaves grew better when a periphyton layer covered these leaves (chapter 5). A somehow surprising positive effect of leaves was the apparent prevention of excessive concentrations of ammonium and nitrite. The results suggest that adding conditioned mangrove leaves might ameliorate negative effects of high protein pellets on the water quality. The high C/N-ratio of leaves tends to balance the stochiometry of the system which may otherwise be dominated by the excessive N-input through CP pellets.

    In the final chapters the interaction among the shrimp larvae themselves, i.e. the effects of stocking density and the release of crowding chemicals and possible alarm pheromones on the shrimp populations are addressed (chapter 6, 7). A strong effect of crowding on shrimp growth and survival was shown. Physical interference stress and cannibalism could be excluded as causal factors. It was thus clear that the effects were caused by other water quality variables. Temperature, pH, salinity, dissolved oxygen, chlorine, nitrite and nitrate appeared of minor influence. However, ammonia toxicity could not be excluded as the causal factor for the observed mortality and reduced growth of P. monodon post-larvae in our experiments.On the other hand, alarm cues, as released by crushed conspecifics had negative effects on post-larval survival at high concentrations (100, 70, 50 and 30 crushed shrimps.l -1 ). Surprisingly, low concentrations of crushed conspecifics (1 crushed shrimp.l -1 ) were shown to have rather stimulatory effects on body size and dry weight.

    Put in an applied perspective, this study suggests simple ways to improve the management of mangrove-shrimp systems. Clearly, mangrove leaves can promote the survival and growth of shrimp post-larvae. However, at high leaf concentrations negative effects may prevail related to a drop in dissolved oxygen and the release of sulphide. A straightforward way to ameliorate such negative effects may be to increase the water flow. This will reduce the risk of local anoxia, and may help spreading the litter over the area, thus avoiding accumulation of these leaves at some sites. The reduction of potentially toxic nitrite and ammonium concentrations by decomposing leaves suggests that mangrove leaves may serve as a useful complement to CP pellets in semi-natural production systems.
    Selected papers of the workshop on integrated management of coastal resources in the Mekong delta, Vietnam
    Mensvoort, M.E.F. van; Quang Tri, Le - \ 2002
    Wageningen : Office C.T. de Wit Graduate School for Production Ecology & Resource Conservation (PE&RC) - ISBN 9789067546744 - 159
    kustgebieden - mangroves - garnalenteelt - landgebruiksplanning - landgebruik - duurzaamheid (sustainability) - hulpbronnenbeheer - vietnam - coastal areas - mangroves - shrimp culture - land use planning - land use - sustainability - resource management - vietnam
    Haemocytic defence in black tiger shrimp (Penaeus monodon)
    Braak, K. van de - \ 2002
    Wageningen University. Promotor(en): E.A. Huisman; W.B. van Muiswinkel; W.P.W. van der Knaap; J.H.W.M. Rombout. - S.l. : S.n. - ISBN 9789058086518 - 159
    penaeus monodon - crustacea - garnalen - immuunsysteem - immuniteitsreactie - immuniteit - verdedigingsmechanismen - via de cel overgebrachte immuniteit - rode bloedcellen - hemolymfe - monoclonale antilichamen - experimentele infectie - infectieziekten - garnalenteelt - penaeus monodon - crustacea - shrimps - immune system - immune response - immunity - defence mechanisms - cell mediated immunity - haemocytes - haemolymph - monoclonal antibodies - experimental infection - infectious diseases - shrimp culture

    Tropical shrimp culture is one of the fastest growing aquaculture sectors in the world. Since this production sector is highly affected by infectious pathogens, disease control is nowadays a priority. Effective prevention methods can be developed more efficiently when quantitative assays for the evaluation and monitoring of the health status of shrimp are available. The defence mechanisms of crustaceans are poorly understood, but knowledge about these is a prerequisite for the development of such health parameters. Therefore, the aim of this thesis was to obtain a better understanding of the defence system of the major cultured shrimp species in the world, Penaeus monodon . The present study emphasised the cellular components of the circulatory system, which play a central role in the haemolymph defence, i.e. the haemocytes.

    To study the usefulness of haemolymph for shrimp health assessment, several cellular and humoral characteristics of P. monodon were determined after haemolymph sampling from the ventral part of the haemocoel (chapter 2). Among other things, five different haemocyte types were distinguished by light microscopy, while electron microscopy revealed granular cells, semigranular cells and hyaline cells. It was concluded that haemolymph characterisation might be a useful tool for health estimation of P. monodon , but that standardisation of the techniques is a prerequisite.

    The use of monoclonal antibodies (mAbs) was proposed as a potential approach for the characterisation of haemocytes. Therefore, a set of mAbs specific for P. monodon haemocytes was produced by immunising mice with haemocyte membrane lysates (chapter 3). Four mAbs (WSH 6, WSH 7, WSH 8 and WSH 16) were selected and extensively characterised. For all mAbs, differences in amount and intensity of the labelling were found between immediately fixed haemocytes and non-fixed cells that were kept in Alsever's solution (AS, an anticoagulant which reduces haemocyte activation) and kept in L15 cell culture medium. WSH 6 reacted with the cell membranes of all fixed haemocytes, while WSH 7 and WSH 16 reacted with the cell membranes of the majority of fixed haemocytes. The membrane labelling appeared to decrease when cells were kept in L15 medium. WSH 8 did not react with the haemocyte membranes. All mAbs reacted with some granules, mainly present in the hyaline cells, when the haemocytes were immediately fixed. When non-fixed cells were kept in AS or in L15 medium, positive granules were also observed in semigranular and granular haemocytes as well as in the largest granules of a fourth cell type, that contains many granules of different sizes and electron densities. Immuno-reactive extracellular fibrous material could be observed when cells were kept in L15 medium. The change in staining pattern was extreme for WSH 8, somewhat less for WSH 6 and WSH 7 and lowest for WSH 16. Double labelling revealed that all mAbs showed a different staining pattern on membranes as well as on granules. WSH 16 also showed labelling in cytoplasmic vesicles, as well as in haemolymph plasma on histological sections. The hypothesis was put forward that immuno-reactive molecules recognised by these mAbs, were related to haemocyte activation factors and that the mAbs could be used in studying haemocyte differentiation, behaviour and function in P. monodon shrimp. Later on, WSH 8 indeed proved suitable for this in immuno-histochemical studies.

    A better characterisation of the immuno-reactive molecules would support the interpretation of the results. In order to investigate whether the mAbs reacted with well-conserved molecules and with haemocytes in animals with molecules that were better characterised than those of P. monodon , a comparative study was carried out (chapter 4). The mAbs also reacted on haemocyte monolayers of the freshwater shrimp Macrobrachium rosenbergii and the two freshwater crayfish Procambarus clarkii and Pacifastacus leniusculus . Immuno-labelling on haemolymph monolayers of the terrestrial isopod crustacean Porcellio scaber (woodlouse) and on coelomic fluid of the annelid Lumbricus terrestris (earthworm) showed partial reactivity. Immuno-reactivity was not observed on haemolymph monolayers of the insect Spodoptera exigua (Florida moth) and the mollusc Lymnaea stagnalis (pond snail), or on blood cell monolayers of the freshwater fish Cyprinus carpio (carp) and of human. On histological sections of M. rosenbergii and P. clarkii , mAb labelling was observed on the haemolymph plasma and on a proportion of the haemocytes. This comparative study showed reactivity of the mAbs in a wide range of crustaceans and related animals and suggests that well conserved molecules were recognised, which may indicate functional importance. Later on, molecules of P. leniusculus that reacted with WSH 6 were better characterised and it was indicated that this molecule could be clotting protein or filamin, which both could be involved in coagulation processes. Unfortunately, the immuno-reactive molecules of P. monodon with WSH 8 could not be characterised further.

    The circulating haemocytes of crustaceans are generally divided into hyaline, semigranular or granular cells, however, this classification is still ambiguous. Not much is known about haemocyte production in penaeid shrimp, but for a better haemocyte classification it is useful to establish how these cells are produced and mature. In order to clarify this, the localisation and (ultra)structure of the haematopoietic tissue and its relation with the circulating haemocytes were studied in chapter 5. The haematopoietic tissue is located in many lobules dispersed in different areas in the cephalothorax, mainly at the dorsal side of the stomach and at the base of the maxillipeds. In order to study the haemocyte production and maturation, shrimp were either injected with LPS, while mitosis was inhibited by vinblastine, or were repeatedly sampled for haemolymph. The presumed precursor cells in the haematopoietic tissue were located towards the exterior of the lobules and maturing young haemocytes towards the inner part, where they can be released into the haemal lacunae. It was proposed that the presumed young haemocytes were generally known as the hyaline cells. Moreover, a new model was proposed where the hyaline cells gave rise to two haemocytic developmental series, i.e., the large- and small-granular cell line. In addition, indications were found that the granular cells of at least the large-granular cell line mature and accumulate in the connective tissue and are easily released into the haemolymph. Light and electron microscopical observations supported the regulation of the haemocyte populations in the circulation by (stored) haemocytes from the connective tissue.

    In order to investigate the clearance reaction of P. monodon haemocytes live Vibrio anguillarum bacteria were injected and the shrimp were periodically sampled (chapter 6). Immuno-double staining analysis with specific antisera against the haemocyte granules and bacteria showed that many haemocytes encapsulated the bacteria at the site of injection. Furthermore, a rapid decrease of live circulating bacteria was detected in the haemolymph. Bacterial clearance in the haemolymph was induced by humoral factors, as observed by agglutinated bacteria, and followed by uptake in different places in the body. Bacteria mainly accumulated in the lymphoid organ, where they, or their degradation products, could be detected for at least seven days after injection. The lymphoid organ consists of folded tubules with a central haemal lumen and a wall, layered with cells. The haemolymph, including the antigens, seemed to migrate from the central tubular lumen through the wall, where the bacteria are arrested and their degradation is started. The lymphoid organ of penaeids is also poorly studied. Electron microscopy of the lymphoid organ revealed the presence of many phagocytic cells that morphologically resemble small-granular haemocytes. It was proposed that haemocytes settle in the tubule walls before they phagocytose. Observations from the present study are similar to clearance mechanisms in the hepatic haemolymph vessels in most decapod crustaceans that do not possess a lymphoid organ.

    Immuno-staining suggested that many of the haemocytes degranulate in the lymphoid organ, producing a layer of fibrous material in the outer tubule wall. These findings might contribute to the reduced haemocyte concentration in the haemolymph of diseased animals or following injection of foreign material. It is proposed that the lymphoid organ is a filter for virtually all foreign material encountered in the haemolymph. Haemocyte degranulation in the lymphoid organ tubule walls could contribute to the filtering capacity of this organ.

    The experimental shrimp appeared to contain many lymphoid organ spheroids, where bacterial antigens were finally also observed. It is proposed that the spheroids have a degradation function for both bacterial and viral material, and that their presence is primarily related to the history of the infectious burden of the shrimp.

    White spot syndrome virus (WSSV) is the pathogen that is a major cause of mortality in shrimp culture in the past decade. In contrast to the extensive study of the morphology and genome structure of the viral pathogen, the defence reaction of the host during WSSV infection is hardly studied. Therefore, the haemocyte response upon experimental WSSV infection was examined in P. monodon shrimp (chapter 7). A strong decline in free circulating haemocytes was detected during severe WSSV infection. The combination of in situ hybridisation with a specific DNA probe to WSSV and immuno-histochemistry with a specific antibody against haemocyte granules was carried out on tissue sections. Haemocytic reactions have never been reported in chronic or acute viral infections in shrimp, but the present results showed that many haemocytes leave the circulation and migrate to tissues where many virus-infected cells are present. However, a subsequent response to the virus-infected cells was not detected. During virus infection, the number of cells in the haematopoietic tissue was also reduced. Moreover, it was suggested that many haemocytes degranulated in the lymphoid organ, producing a similar but more obvious layer of fibrous material in the outer tubule wall than after bacterial injection.

    The obtained results are summarised and discussed in chapter 8. Furthermore, the results described in chapters 6 and 7 were used to refine the proposed model of chapter 5. The haemocytes of the small-granular cell line are suggested to mature and carry out their function in the lymphoid organ. The results of the present research emphasise the rapid activation of the haemocytes after stimulation of the animal and illustrate several relevant functions of those cells. The present knowledge provides reliable grounds for further discussions about production, maturation and activation of the haemocytes in penaeid shrimp and possibly also in related animals like other shrimp species, crayfish, lobsters and crabs. Knowledge of the functioning of the defence system is of extreme importance since stimulation of this system is considered as a potential intervention strategy in shrimp culture to overcome the infectious diseases.

    The first WEFTA intercomparison exercise on the determination of sulphite in tropical shrimps
    Luten, J.B. ; Bouquet, W. - \ 1993
    IJmuiden : RIVO-DLO (RIVO report C012/93)
    dierlijke producten - chemicaliën - voedseladditieven - voedselbewaring - voedselconserveermiddelen - voedingsmiddelen - steurgarnalen - garnalenteelt - garnalen - sulfieten - animal products - chemicals - food additives - food preservation - food preservatives - foods - prawns - shrimp culture - shrimps - sulfites
    Research into the development of an integrated and sustainable system of Panaeid shrimps, Artemia and salt in the operating salinas in the coastal area of the Vietnamese Mekong Delta : final report, Jan. 1990 - July 1992
    Brands, J.T. - \ 1993
    Wageningen : IMAG-DLO - 144
    artemia - brakwater - branchiopoda - extractie - visteelt - mijnbouw - steurgarnalen - zout - zeewater - garnalenteelt - garnalen - vietnam - artemia - brackish water - branchiopoda - extraction - fish culture - mining - prawns - salt - sea water - shrimp culture - shrimps - vietnam
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