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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    Data from: Genetic diversity of Nile tilapia (Oreochromis niloticus) throughout West Africa
    Lind, Curtis E. ; Agyakwah, Seth K. ; Attipoe, Felix Y. ; Nugent, Christopher ; Crooijmans, Richard ; Toguyeni, Aboubacar - \ 2019
    Commonwealth Scientific and Industrial Research Organization (CSIRO)
    tilapia - single nucleotide polymorphism (SNP) - Oreochromis niloticus - West Africa - population genetics - Aquaculture
    Nile tilapia (Oreochromis niloticus) is a globally significant aquaculture species rapidly gaining status as a farmed commodity. In West Africa, wild Nile tilapia genetic resources are abundant yet knowledge of fine-scale population structure and patterns of natural genetic variation are limited. Coinciding with this is a burgeoning growth in tilapia aquaculture in Ghana and other countries within the region underpinned by locally available genetic resources. Using 192 single nucleotide polymorphism (SNP) markers this study conducted a genetic survey of Nile tilapia throughout West Africa, sampling 23 wild populations across eight countries (Benin, Burkina Faso, Côte d’Ivoire, Ghana, Togo, Mali, Gambia and Senegal), representing the major catchments of the Volta, Niger, Senegal and Gambia River basins. A pattern of isolation-by-distance and significant spatial genetic structure was identified throughout West Africa (Global FST = 0.144), which largely corresponds to major river basins and, to a lesser extent, sub-basins. Two populations from the Gambia River (Kudang and Walekounda), one from the western Niger River (Lake Sélingué) and one from the upper Red Volta River (Kongoussi) showed markedly lower levels of diversity and high genetic differentiation compared to all other populations, suggesting genetically isolated populations occurring across the region. Genetic structure within the Volta Basin did not always follow the pattern expected for sub-river basins. This study identifies clear genetic structuring and differentiation amongst West African Nile tilapia populations, which concur with broad patterns found in previous studies. In addition, we provide new evidence for fine-scale genetic structuring within the Volta Basin and previously unidentified genetic differences of populations in Gambia. The 192 SNP marker suite used in this study is a useful tool for differentiating tilapia populations and we recommend incorporating this marker suite into future population screening of O. niloticus. Our results form the basis of a solid platform for future research on wild tilapia genetic resources in West Africa, and the identification of potentially valuable germplasm for use in ongoing breeding programs for aquaculture.
    Feeds, water quality, gut morphology and digestion in Nile tilapia (Oreochromis niloticus)
    Trần Ngọc Thiên Kim, Kim - \ 2017
    Wageningen University. Promotor(en): J.A.J. Verreth, co-promotor(en): J.W. Schrama; Arjen J. Roem. - Wageningen : Wageningen University - ISBN 9789463431484 - 127
    tilapia - oreochromis niloticus - feeds - fish feeding - water quality - digestion - digestibility - intestines - morphology - fish culture - aquaculture - tilapia - oreochromis niloticus - voer - visvoeding - waterkwaliteit - spijsvertering - verteerbaarheid - darmen - morfologie - visteelt - aquacultuur

    Diet composition, ingredient and nutrients, are important to consider for maintaining intestinal functions. Studies on both positive (using feed additives) and negative effects (using high inclusion of plant ingredients) of fish feeds are numerous, however, between studies results are often highly variable, both in type of response and in significance. The central hypothesis of this study was that adverse environmental conditions may aggravate negative effects of plant ingredients on the intestinal functions to the extent that mild effects become severe and perceptible. To do so, dietary factors and environmental conditions were evaluated and the interaction between diet composition and environmental conditions were studied in Nile tilapia.

    In Chapter 2, six common raw materials including hydrolysed feather meal (HFM), soybean meal (SBM), rice bran (RB), rapeseed meal (RM), sunflower meal (SFM) and dried distiller grains with solubles (DDGS) were chosen to determine the effect of nutrient digestibility, nitrogen/energy balance and changes in intestinal morphology. The study demonstrated that feed ingredients do have an impact on the alteration in intestinal parameters, but also on the nutrient digestibility and the nitrogen/energy balance. Although being well digested, soybean meal caused the most obvious alteration in the intestinal morphology. These alterations were not related to the nutrient digestibility nor to nitrogen/energy balance parameters. Soybean meal, causing the most alterations in the intestinal morphology, was further used in all subsequent chapters of this thesis.

    Chapter 3 and 4 described the interaction between diet composition and environmental conditions on the intestinal functions. This was studied with two different environmental conditions, dissolved oxygen (Chapter 3) and salinity (Chapter 4). These two chapters evaluated whether suboptimal environmental conditions (low dissolved oxygen or elevated salinity in water) may interact with a soybean meal based diet in nutrient digestion and intestinal morphology of tilapia. The study demonstrated that environmental stressors can aggravate/reveal the negative intestinal morphology changes induced by a soybean meal based diet. However, these effects of adverse environmental conditions on the intestinal functions were not homogenously dispersed over the whole intestinal length. The effect of salinity on the intestinal morphology occurred predominantly in the distal intestine, whereas the effect of low oxygen concentration was more visible at the proximal intestine. Alterations in the intestinal morphology, as found in this study, have wider effects on the performance of the affected fish. In Chapter 3, the protein digestibility decreased under hypoxic conditions at week 8, which parallels with the time related alteration in intestinal morphology. Chapter 4 showed that when fish were raised at 15 ‰ salinity, nutrient digestibility increased; however, this positive effect decreased when the intestinal morphology changed. The study also found that the combined effect of a soybean meal based diet and hypoxia was stronger compared to the combination with elevated salinity. Therefore, the combination with hypoxia was further used in the next study of this thesis.

    In Chapter 5, the combination of hypoxic condition and a soybean meal based diet was chosen to test the hypothesis that only under stressful conditions, the effects of feed additives can be noticed. The impact of two dietary organic acids, formic acid and butyric acid, on nutrient digestibility and intestinal morphology was determined under optimal (normoxia) and suboptimal conditions (hypoxia). The results showed that although organic acids did not significantly improve growth performance and nutrient digestibility under normoxic condition, they did so under hypoxic conditions. Fish fed organic acid supplemented diets all showed improvements in the morphology of intestine under normoxic conditions, and these effects were more enhanced under hypoxic conditions. This indicates that environmental conditions can alter the effect of organic acid on nutrient digestibility and intestinal morphology in tilapia.

    Finally, Chapter 6 provided a synthesis of the main findings, and a reflection on the methodologies used in Chapters 2-5 as well as a discussion on the relevance of this study to aquaculture. It is concluded that although being well digested, soybean meal caused the most obvious alteration in intestinal morphology. The adverse environmental conditions aggravated negative effects of soybean meal based diets on the intestinal functions to the extent that mild effects become severe and visible. The negative effect on intestinal morphology of soybean meal in the diet is enhanced at low oxygen level and at elevated salinity. The effect of salinity on the intestinal morphology occurs predominantly in the distal intestine, whereas the effect of low oxygen concentration is more visible at the proximal intestine. The thesis indicated that the impact of organic acids on intestinal functions is dependent on environmental conditions, being more pronounced under challenging conditions (e.g. hypoxia). Therefore, studies on both positive (using feed additives) and negative effects (using high inclusion of plant ingredients) of dietary factors should be done under suboptimal conditions.

    Optimization of breeding schemes for Nile tilapia (Oreochromis niloticus) in smallholder production systems in Kenya
    Omasaki, Simion Kipkemboi - \ 2017
    Wageningen University. Promotor(en): J. Komen, co-promotor(en): J.A.M. Arendonk; A.K. Kahi. - Wageningen : Wageningen University - ISBN 9789463431064 - 167
    oreochromis niloticus - tilapia - breeding programmes - selective breeding - genetic improvement - small farms - sustainability - fish culture - aquaculture - kenya - oreochromis niloticus - tilapia - veredelingsprogramma's - selectief fokken - genetische verbetering - kleine landbouwbedrijven - duurzaamheid (sustainability) - visteelt - aquacultuur - kenya

    The aim of this thesis was to develop a sustainable low cost breeding program for Nile tilapia that addresses both genetic and economic aspects of smallholder fish farmers in Kenya. First, Analytical Hierarchy Process Technique was used to define a breeding goal based on farmer’s preferences for traits. Farmers’ preferences for traits differed significantly depending on income and market orientation. Low and medium income farmers preferred harvest weight (HW) while high income farmers preferred growth (GR) and survival (S) traits. Grouping farmers according to market objective (fingerling production or fattening) showed that fingerling producers preferred GR and S while fattening farmers preferred HW and S. Consensus preference values were obtained using weighted goal programming and these values were used to derive desired gains for a breeding goal that takes into account farmers’ diverse backgrounds and preferences for traits. Secondly, the existence of genetic variation for traits of interest was investigated. Substantial additive genetic effects for HW, GR and shape traits were present that can be exploited through selection under low input production system. Heritability estimates for HW, GR and shape were 0.21 ± 0.03, 0.26 ± 0.04 and 0.12 ± 0.03 for mixed sex (nucleus) respectively. The calculation of economic values for breeding goal traits revealed that economic values for GR differed depending on the definition of the breeding goal and that selection for feed efficiency is the key factor to economic profitability of Nile tilapia breeding programs. A significant genotype by environment re-ranking was found for GR between the mixed sex nucleus and monosex production environments. Genotype by environment interaction (G x E) led to lower genetic gain for GR in production environment. Incorporating sib information from monosex production environment into the selection index resulted in a more accurate estimation of breeding values which increased genetic gain in growth. Using desired gain approach, weights for desired gains in harvest weight, growth rate and survival were derived that maximized genetic gains for these breeding goal traits. It is concluded that these results can be used to develop a sustainable centralized breeding program. However, a reliable well planned and organized decentralized strategy for dissemination of genetically improved fry of Nile tilapia to farmers is paramount.

    Aquaculture Innovation in Vietnam
    Rurangwa, E. ; Baumgartner, U. ; Nguyen, H.M. ; Vis, J.W. van de - \ 2016
    Yerseke : Wageningen Marine Research (Wageningen Marine Research report C097/16) - 28
    aquaculture - innovations - tilapia - fishes - shrimps - crabs - vietnam - aquacultuur - innovaties - tilapia - vissen - garnalen - krabben (schaaldieren) - vietnam
    Microbial interactions in the fish gut
    Giatsis, Christos - \ 2016
    Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Marc Verdegem; Detmer Sipkema. - Wageningen : Wageningen University - ISBN 9789462578777 - 196
    fishes - tilapia - larvae - microbial interactions - intestinal microorganisms - intestines - dynamics - fish feeding - probiotics - fish culture - aquaculture - vissen - tilapia - larven - microbiële interacties - darmmicro-organismen - darmen - dynamica - visvoeding - probiotica - visteelt - aquacultuur

    Aquaculture has realized considerable growth over the past years while the world demand on seafood has been increasing. As aquaculture intensifies, the production sector needs to tackle major bottlenecks such as suboptimal growth and high and unpredictable mortality, especially in larval cultures. Fish-microbe interactions are closely related to overall fish health. To obtain a healthy and resilient microbial community (MC), it is important to understand the underlying mechanisms of microbial colonization in the fish gut.

    The goal of this thesis was to investigate the role of water and feed microbial communities on shaping gut communities during early development of Nile tilapia.

    To determine the contribution of stochasticity to overall variation, we first characterized the spatio-temporal variation in MC composition between individuals reared within the same or in replicate recirculating or active suspension systems (RAS vs. AS). Highly similar MCs developed in the gut when larvae shared the same water and diet. Rearing larvae in replicate production systems resulted in significantly different gut communities indicating that compositional replication of the MCs of an ecosystem is not fully predictable. We found that mainly water MCs, and to a lesser degree feed MCs, were associated with changes in MCs. Thus, we could conclude that steering gut MCs can be possible through water MC management tailored on the specifications of the rearing system in use.

    Next, the possibility of early life steering of gut communities via microbial manipulations of feed MCs was explored. We hypothesized that gut microbial composition is strongly shaped by selective pressures in the gut and by the MCs present in the water. Thus similar MCs should develop between treatments regardless of the dietary treatments. Fish larvae were fed either a control feed or the control feed containing MCs derived from aerobic, methanogenic or denitrifying sludge reactors. We found that gut microbiota shared a much higher number of operational taxonomic units (OTUs) with microbiota in sludge-based feeds than with water, resulting in distinct gut MCs between treatments. Our findings suggest that Nile tilapia gut MC has a certain plasticity, which makes it amenable to interventions through proper feed microbial management.

    Subsequently, we tested the imprinting effect of early exposure to the probiotic Bacillus subtilis on shaping gut MC composition even after the administration of the probiotic discontinues. For this, we constrained the initial contact with microbes from the environment by producing axenic tilapia larvae, which were then exposed to normal husbandry conditions. Early life probiotic exposure affected gut MC composition during B. subtilis administration but also within the first two weeks after its administration stopped, thus indicating that early exposure to the probiotic strain via the water had a sustained impact on gut MC composition.

    Finally, overall conclusions and practical implications of our results for aquaculture production were presented. A meta-analysis was also performed to examine (1) the phylogenetic similarity among gut MCs of the same and different fish species reared in different habitats, fed different diets and at different developmental stages and (2) the factors primarily shaping gut MCs. We showed that the selective pressure responsible in shaping gut MC composition highly depends on the host as gut communities clustered primarily together by host and to a lesser extent reflected differences in habitat and diet. The phylogenetic analysis of gut communities revealed a clear clustering by study thus indicating that manipulation of gut communities is conceivable. Study-to-study variation could be attributed to the methodology used for MC analysis highlighting also the importance of methodological uniformity when comparisons between studies are made.

    Overall, this thesis provided fundamental knowledge on MC composition and development in aquaculture rearing systems. Although the insights generated by this thesis are still premature to fully explain, predict or steer MC composition, and though additional studies are needed, we believe that, in the long run, this approach will facilitate the development of safe and effective methods for manipulating gut microbial composition to promote fish health in aquaculture rearing systems.

    Investigating the suitability of constructed wetlands for the treatment of water for fish farms
    Heijden, P.G.M. van der; Dien, F. van; El-Beshbishi, D.A. - \ 2015
    Wageningen : Centre for Development Innovation, Wageningen UR (Report / CDI 15-079) - 27
    wetlands - artificial wetlands - fish farms - heavy metals - farming - pesticides - waste water - tilapia - development projects - egypt - north africa - africa - wetlands - helofytenfilters - viskwekerijen - zware metalen - landbouw bedrijven - pesticiden - afvalwater - tilapia - ontwikkelingsprojecten - egypte - noord-afrika - afrika
    Many fish farms in Egypt rely on water of drainage canals to fill the fish ponds. There is a risk that this water is contaminated with pesticides and heavy metals. This report describes the results of a collaborative project that took place in 2012-2014 and that aimed to test the suitability of a constructed (engineered) wetland as treatment device for the removal of such pollutants from drainage canal water on a private fish farm in Egypt
    Development of Aquaculture in Ghana: Analysis of the fish value chain and potential business cases
    Rurangwa, E. ; Agyakwah, S.K. ; Boon, H. ; Bolman, B.C. - \ 2015
    Yerseke : IMARES (IMARES report C021/15) - 59
    zoetwateraquacultuur - ghana - waardeketenanalyse - investeringsplannen - aquacultuur en milieu - visproductie - stakeholders - tilapia - oreochromis niloticus - freshwater aquaculture - ghana - value chain analysis - investment planning - aquaculture and environment - fish production - stakeholders - tilapia - oreochromis niloticus
    The main aim of this study was to assess the feasibility of the formation and set-up of one or more Public Private Partnerships (PPPs) for aquaculture in Ghana. The project consisted of two phases. The first phase was a value chain analysis (VCA) of aquaculture in Ghana to identify bottlenecks and business opportunities. The second phase was to develop business cases for investments in aquaculture in Ghana. Since the demand for Tilapia in Ghana is very high, the focus of this study is mainly on Tilapia.
    Gevolgen stresshormonen op de stofwisseling (algemene informatie) : wat stress bij vis doet
    Leenstra, S.H. ; Scheerboom, J. - \ 2014
    Aquacultuur 29 (2014)4. - ISSN 1382-2764 - p. 25 - 28.
    aquacultuur - vissen - stressfysiologie - palingteelt - tilapia - aquaculture - fishes - stress physiology - eel culture - tilapia
    Stress bij vissen kreeg in dit vakblad nog niet de aandacht die het verdient. Terwijl viskwekers al lang weten hoe ingrijpend de gevolgen van stress voor de productie kunnen zijn. Bovendien zijn wetenschappers nu in staat stress te meten en kwantificeren. De auteurs vroegen zich af hoe de stofwisseling van vissen door stress kan worden beïnvloed en welke negatieve gevolgen dit heeft.
    Waterkwaliteit in recirculatie systemenen
    Eding, Ep - \ 2014
    water quality - aquaculture - fish culture - recirculating aquaculture systems - recirculating systems - tilapia
    Vibrio vulnificus outbreaks in Dutch eel farms since 1996: strain diversity and impact.
    Haenen, O.L.M. ; Zanten, E. van; Jansen, R. ; Roozenburg, I. ; Engelsma, M.Y. ; Dijkstra, A. ; Boers, S.A. ; Voorbergen-Laarman, M. ; Möller, A.V.M. - \ 2014
    Diseases of Aquatic Organisms 108 (2014)3. - ISSN 0177-5103 - p. 201 - 209.
    diseased european eel - anguilla-anguilla - biotype 2 - clinical-manifestations - fresh-water - serovar-e - infection - pathogen - tilapia - fish
    Vibrio vulnificus is a potentially zoonotic bacterial pathogen of fish, which can infect humans (causing necrotic fasciitis). We analysed 24 V. vulnificus isolates (from 23 severe eel disease outbreaks in 8 Dutch eel farms during 1996 to 2009, and 1 clinical strain from an eel farmer) for genetic correlation and zoonotic potential. Strains were typed using biotyping and molecular typing by high-throughput multilocus sequence typing (hiMLST) and REP-PCR (Diversilab®). We identified 19 strains of biotype 1 and 5 of biotype 2 (4 from eels, 1 from the eel farmer), that were subdivided into 8 MLST types (ST) according to the international standard method. This is the first report of V. vulnificus biotype 1 outbreaks in Dutch eel farms. Seven of the 8 STs, of unknown zoonotic potential, were newly identified and were deposited in the MLST database. The REP-PCR and the MLST were highly concordant, indicating that the REP-PCR is a useful alternative for MLST. The strains isolated from the farmer and his eels were ST 112, a known potential zoonotic strain. Antimicrobial resistance to cefoxitin was found in most of the V. vulnificus strains, and an increasing resistance to quinolones, trimethoprim + sulphonamide and tetracycline was found over time in strain ST 140. Virulence testing of isolates from diseased eels is recommended, and medical practitioners should be informed about the potential risk of zoonotic infections by V. vulnificus from eels for the prevention of infection especially among high-risk individuals. Additional use of molecular typing methods such as hiMLST and Diversilab® is recommended for epidemiological purposes during V. vulnificus outbreaks.
    Supporting the Aquaculture industry in Egypt: Identification mission 30 March - 1 April 2014
    Rothuis, A.J. - \ 2014
    Yerseke : IMARES (Report / IMARES Wageningen UR C062/14) - 11
    aquacultuur - viskwekerijen - tilapia - rentabiliteit - egypte - aquaculture - fish farms - tilapia - profitability - egypt
    Egyptian fish farming has witnessed a spectacular development resulting in an industry that is number 7 worldwide and number two in tilapia production. As such the industry is an important contributor to Egypt’s economy as well as a major provider of cheap fish protein. However, there are a number of developments that potentially could result in a stagnation or even collapse of the industry. Some important issues are: • Low fish prices and increasing fish production costs resulting in eroding profitability of farms and thus no investment in technology development and innovation. • Lack of processing and freezing capacity which results in an inability to access new export markets • Low priority of government, lack of legislation and harmonisation of legislation, no operational extension service, weak professional organisations and weak linkage between research and industry • Rather traditional farming technology (tilapia) including use of low quality feeds and wild fry (marine aquaculture). The IMARES/Wageningen UR study1 illustrated that within the currently available land and water resources, Egypt can potentially increase its total tilapia production from 700,000 tonnes to 1,400,000 tonnes, resulting in an increase in the economic value of the sector to over 1% of the current GDP. In order to realize this potential, the first requirement is to increase the current farm profitability. When this is realized, capital will become available that allow farmers to invest into new production technologies, market innovations and new organisational structures, that will than result in more fish and new markets. Among the issues at stake are improvements in fish feed and on-farm feed management, breeding and genetics and export of fish to new international markets (Middle East and Europe).
    World Aquaculture Society Asia-Pacific Conference, Ho Chi Minh, Vietnam
    Tran, Kim - \ 2013
    Asian-Pacific Aquaculture 2013
    Schrama, Johan - \ 2013
    Asian-Pacific Aquaculture 2013
    Roem, Arjen - \ 2013
    Asian-Pacific Aquaculture 2013
    Verreth, Johan - \ 2013
    Asian-Pacific Aquaculture 2013
    Jaklofsky, M.T.J. - \ 2013
    Effect of plant feedstuffs on nutritional physiology and gut histology of tilapia - Preliminary results/ presentation
    Was Lates Late? A Null Model for the Nile Perch Boom in Lake Victoria
    Downing, A.S. ; Galic, N.G. ; Goudswaard, P.C. ; Nes, E.H. van; Scheffer, M. ; Witte, F. ; Mooij, W.M. - \ 2013
    PLoS ONE 8 (2013)10. - ISSN 1932-6203
    east-africa - niloticus l - fisheries - impact - ecosystems - resurgence - lessons - tilapia - kyoga - l.
    Nile perch (Lates niloticus) suddenly invaded Lake Victoria between 1979 and 1987, 25 years after its introduction in the Ugandan side of the lake. Nile perch then replaced the native fish diversity and irreversibly altered the ecosystem and its role to lakeshore societies: it is now a prised export product that supports millions of livelihoods. The delay in the Nile perch boom led to a hunt for triggers of the sudden boom and generated several hypotheses regarding its growth at low abundances – all hypotheses having important implications for the management of Nile perch stocks. We use logistic growth as a parsimonious null model to predict when the Nile perch invasion should have been expected, given its growth rate, initial stock size and introduction year. We find the first exponential growth phase can explain the timing of the perch boom at the scale of Lake Victoria, suggesting that complex mechanisms are not necessary to explain the Nile perch invasion or its timing. However, the boom started in Kenya before Uganda, indicating perhaps that Allee effects act at smaller scales than that of the whole Lake. The Nile perch invasion of other lakes indicates that habitat differences may also have an effect on invasion success. Our results suggest there is probably no single management strategy applicable to the whole lake that would lead to both efficient and sustainable exploitation of its resources.
    Effect of three innovative culture systems on water quality and whitespot syndrome virus (WSSV) viral load in WSSV-fed Penaeus monodon cultured in indoor tanks
    Alapide-Tendencia, E.V. ; Bosma, R.H. ; Rose Sorio, L. - \ 2012
    Aquaculture 350-353 (2012). - ISSN 0044-8486 - p. 169 - 174.
    vibrio-harveyi - litopenaeus-vannamei - chlorella-vulgaris - shrimp ponds - bacteria - mortalities - microalgae - juveniles - tilapia - growth
    White spot syndrome virus is the most important among the shrimp diseases. It has been devastating the shrimp industry for more than 3 decades. Previous studies reported that greater percentage of yellow colonies on thiosulfate citrate bile salt sucrose agar (yellow vibrios) in the rearing water, abundant supply of natural food such as Chlorella, and the use of the greenwater technology (GW) are some ecological ways of preventing WSSV outbreak. The aim of this study was to investigate the efficiency of the 3 systems against WSSV. Shrimp, experimentally infected with WSSV by feeding with WSSV positive shrimp carcass, was cultured in tanks using three treatments: with tilapia to simulate the GW, seeded with Chlorella, and with molasses added to enhance growth of yellow vibrios. Shrimp cultured in seawater served as the control. Survival was recorded and shrimp were analyzed for WSSV quantification using qPCR upon termination. Analysis showed no significant differences in shrimp survival at 120 h post infection in all treatments and the control. However, from the original viral load of 1.40 × 101 WSSV/mg sample, WSSV decreased and was significantly lowest in shrimp cultured using GW (7.0 × 100), compared to the control (4.82 × 105) and the other treatments (3.66 × 105 for molasses added and 4.64 × 105 for Chlorella seeded) in which viral load increased 4–5 times. Shrimp survival was highest in Chlorella seeded treatment and lowest in GW. Nitrogenous waste concentrations were lowest in molasses added water and highest in GW. Results suggest that the GW culture technology provides protection against WSSV while addition of molasses lowers nitrogenous waste concentration. The use of GW in combination with the addition of molasses for shrimp culture is suggested.
    Whitefish wars: Pangasius, politics and consumer confusion in Europe
    Little, D.C. ; Bush, S.R. ; Belton, B. ; Nguyen Thanh Phuong, ; Young, J.A. ; Murray, F.J. - \ 2012
    Marine Policy 36 (2012)3. - ISSN 0308-597X - p. 738 - 745.
    sutchi catfish - fish - sustainability - vietnam - aquaculture - governance - fisheries - tilapia - market - trends
    Rapid growth in production of the farmed Vietnamese whitefish pangasius and its trade with the European Union has provoked criticism of the fish’s environmental, social and safety credentials by actors including WWF and Members of the European Parliament and associated negative media coverage. This paper reviews the range of claims communicated about pangasius (identified as a form of mass mediated risk governance), in light of scientific evidence and analysis of data from the EU’s Rapid Alert System for Food and Feeds food safety notification system for imported seafood. This analysis shows pangasius to be generally safe, environmentally benign and beneficial for actors along the international value chains that characterise the trade. The case is made that increasingly politicised debates in Europe around risk and uncertainty are potentially counterproductive for EU seafood security and European aquaculture industry, and that the trade in pangasius can contribute to sustainable seafood consumption in a number of ways. Transparent evidence-based assessment and systems for communicating complex issues of risk for products such as pangasius are required in order to support continuance of fair and mutually beneficial trade.
    Een zelfgebouwd recirculatiesysteem in Egypte
    Heijden, P.G.M. van der - \ 2009
    Aquacultuur 5 (2009). - ISSN 1382-2764 - p. 21 - 26.
    aquacultuur - tilapia - egypte - visserij - aquaculture - tilapia - egypt - fisheries
    In Aquacultuur nr 6, 2007, beschreef Bert-Jan Roosendaal het Egyptian Aquaculture Centre, een commerciële tilapiakwekerij annex opleidingscentrum van dr. Ismail Radwan. Deze man, die voor de ontwikkeling van de tilapiateelt in Egypte van groot belang was en is, heeft ook deelgenomen aan een korte cursus over visteelt in recirculatiesystemen en aan een studiereis langs enkele Nederlandse viskwekerijen die beide door Wageningen International zijn georganiseerd. Tijdens een recent bezoek aan zijn bedrijf konden we zien hoe de in Nederland opgedane kennis door dr. Radwan in praktijk wordt gebracht
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