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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    Inhibition of methyltransferase activity of enhancer of zeste 2 leads to enhanced lipid accumulation and altered chromatin status in zebrafish
    Broeder, Marjo J. den; Ballangby, Jarle ; Kamminga, Leonie M. ; Aleström, Peter ; Legler, Juliette ; Lindeman, Leif C. ; Kamstra, Jorke H. - \ 2020
    Epigenetics and Chromatin 13 (2020)1. - ISSN 1756-8935 - 1 p.
    ATAC-seq - Epigenetics - Histone methyl transferases - Metabolism - Zebrafish

    BACKGROUND: Recent studies indicate that exposure to environmental chemicals may increase susceptibility to developing metabolic diseases. This susceptibility may in part be caused by changes to the epigenetic landscape which consequently affect gene expression and lead to changes in lipid metabolism. The epigenetic modifier enhancer of zeste 2 (Ezh2) is a histone H3K27 methyltransferase implicated to play a role in lipid metabolism and adipogenesis. In this study, we used the zebrafish (Danio rerio) to investigate the role of Ezh2 on lipid metabolism and chromatin status following developmental exposure to the Ezh1/2 inhibitor PF-06726304 acetate. We used the environmental chemical tributyltin (TBT) as a positive control, as this chemical is known to act on lipid metabolism via EZH-mediated pathways in mammals. RESULTS: Zebrafish embryos (0-5 days post-fertilization, dpf) exposed to non-toxic concentrations of PF-06726304 acetate (5 μM) and TBT (1 nM) exhibited increased lipid accumulation. Changes in chromatin were analyzed by the assay for transposase-accessible chromatin sequencing (ATAC-seq) at 50% epiboly (5.5 hpf). We observed 349 altered chromatin regions, predominantly located at H3K27me3 loci and mostly more open chromatin in the exposed samples. Genes associated to these loci were linked to metabolic pathways. In addition, a selection of genes involved in lipid homeostasis, adipogenesis and genes specifically targeted by PF-06726304 acetate via altered chromatin accessibility were differentially expressed after TBT and PF-06726304 acetate exposure at 5 dpf, but not at 50% epiboly stage. One gene, cebpa, did not show a change in chromatin, but did show a change in gene expression at 5 dpf. Interestingly, underlying H3K27me3 marks were significantly decreased at this locus at 50% epiboly. CONCLUSIONS: Here, we show for the first time the applicability of ATAC-seq as a tool to investigate toxicological responses in zebrafish. Our analysis indicates that Ezh2 inhibition leads to a partial primed state of chromatin linked to metabolic pathways which results in gene expression changes later in development, leading to enhanced lipid accumulation. Although ATAC-seq seems promising, our in-depth assessment of the cebpa locus indicates that we need to consider underlying epigenetic marks as well.

    Influence of rate of salinity increase on nitrifying biofilms
    Navada, Sharada ; Vadstein, Olav ; Tveten, Ann-Kristin ; Verstege, Gerhardus C. ; Terjesen, Bendik Fyhn ; Mota, Vasco C. ; Venkataraman, Vishwesh ; Gaumet, Frédéric ; Mikkelsen, Øyvind ; Kamstra, Andries - \ 2019
    Journal of Cleaner Production 238 (2019). - ISSN 0959-6526
    A strategy for rapid increase in salinity with minimal impact on nitrification is important for ammonia removal from saline effluents, especially in recirculating aquaculture systems with high water reuse. To study the influence of the rate of salinity increase on nitrification, continuously operated moving bed biofilm reactors were transferred from freshwater (0‰ salinity) to seawater (32‰ salinity) at five different rates of salinity change: 0 (control), 1, 2, 6, and 15‰ day−1. Each daily change was conducted gradually overnight. The results showed that at salinities higher than 4–8‰, the ammonia oxidation capacity decreased linearly with salinity and reduced by 50–90% upon complete seawater transfer, with the greatest reduction in the 1‰ day−1 treatment. Thereafter, it increased linearly with time, with little difference between treatments. Overall, the biofilm microbial communities in the control and the 15‰ day−1 treatment were highly similar, while those in the other treatments shifted significantly with time and had greater species diversity, richness, and evenness of nitrifiers. Candidatus Nitrotoga was the dominant nitrite oxidizing bacteria in all treatments throughout the study, indicating that this recently discovered group may tolerate salinities up to 32‰. The results suggest that although the rate of salinity increase influences the microbial community composition, it only weakly influences ammonia oxidation capacity, which mainly depends on salinity and seawater acclimatization time. Therefore, for rapid seawater acclimatization of freshwater nitrifying biofilms, increasing the salinity continuously in two days may be a better strategy than increasing the salinity over a month, provided an initial decrease in ammonia oxidation is acceptable. The findings can aid in the shift from net-pen fish farming to recirculating aquaculture systems, thereby lowering the ecological impacts of seafood production.
    Mixing and scale affect moving bed biofilm reactor (MBBR) performance
    Kamstra, Andries ; Blom, Ewout ; Terjesen, Bendik Fyhn - \ 2017
    Aquacultural Engineering 78 (2017). - ISSN 0144-8609 - p. 9 - 17.
    Moving Bed Biofilm Reactors (MBBR) are used increasingly in closed systems for farming of fish. Scaling, i.e. design of units of increasing size, is an important issue in general bio-reactor design since mixing behaviour will differ between small and large scale. Research is mostly performed on small-scale biofilters and the question is to what extent this can be upscaled to a commercial level. Therefore, the objective of this research was to establish the effect of mixing and scale on MBBR performance. The research was done in two major parts; firstly effects of scale-sensitive factors were studied in small reactors. Secondly, performance of these small reactors was then compared to increasingly large reactor sizes, using the same inlet water quality and biofilm. Firstly, a 200 L MBBR (medium scale) was operated continuously using a synthetic feed solution. Biofilm carriers from this reactor was used for short-term experiments in 0.8 L reactors (small scale) and compared with the performance of the 200 L medium scale reactor. Reactor geometry and superficial air velocity (m h−1) were identical in these experiments. Subsequently, the small reactors were incubated with biofilm carriers from three commercial farms and performance compared with these large scale reactors. In a number of additional experiments the effect of mixing and Total Ammonia Nitrogen (TAN) was tested at small and medium scale. The results showed that MBBR scale has a significant effect on TAN removal rate. In general, the larger the scale the better the performance. TAN removal (rTAN) at small scale (0.8 L) is about 80% compared to that at medium scale (200 L). The difference between small scale and large scale (> 20 m3) is even higher. These findings warrant further studies on whether a plateau is reached in rTAN at a certain scale; a study which will have considerable importance for optimal design and dimensioning of commercial scale RAS. It was further found that superficial air velocity is not a good scaling factor for MBBRs. Upscaling while maintaining geometry implies increasing air injection depth and therefore increased energy input will be required at a comparable superficial air velocity, which is not incorporated in the superficial air velocity term (m h−1). Superficial air velocity and media filling% were found to have a strong effect on mixing time at small scale. An air velocity below a threshold of 5 m h−1 decreased TAN removal at both small and medium scale. Intense mixing at small scale increased TAN removal at low TAN concentration. However, at a high TAN concentration, the small scale MBBR always performed at not more than 80% of the capacity of the medium scale system, irrespective of the mixing conditions. Hence, the capacity of full scale systems will be under-estimated when based solely on small scale experiments.
    Constraining Is Enabling? Exploring the Influence of National Context on Civil Society Strength
    Kamstra, Jelmer ; Pelzer, Ben ; Elbers, Willem ; Ruben, Ruerd - \ 2016
    VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations (2016). - ISSN 0957-8765 - p. 1023 - 1044.
    Associational membership - Civil society - Cross-national analysis - Developing countries - Enabling environment - Multilevel analysis

    This article analyses the influence of national context on civil society strength based on four key dimensions: level of democracy, political stability, rule of law and economic development. Whereas existing studies mainly focus on Western and post-communist countries, we explicitly include developing countries in our analysis. We use associational membership as proxy for civil society strength and include data of 53 countries. Rule of law, economic development and (to a lesser extent) political stability emerge from our multilevel regression models as the main factors affecting civil society membership. Unlike previous studies, we show that these relations are quadratic instead of linear. This means that where existing theories predict a drop in memberships in developing countries, we find a rise. In other words, harsh conditions actually strengthen civil society in terms of membership levels. We argue that this could be the case because reasons for CSO membership are essentially different in the developed and in the developing world. Contrary to theoretical assumptions, democratic rights do not appear critically important for civil society membership.

    Effects of diet composition and ultrasound treatment on particle size distribution and carbon bioavailability in feces of rainbow trout
    Meriac, A. ; Tilburg, T. van; Eding, E.H. ; Kamstra, A. ; Schrama, J.W. ; Verreth, J.A.J. - \ 2015
    Aquacultural Engineering 65 (2015). - ISSN 0144-8609 - p. 10 - 16.
    recirculating aquaculture systems - activated-sludge - anaerobic-digestion - waste-water - feed - fish - denitrification - digestibility - pretreatment - sonication
    The effect of a high and low non-starch polysaccharide diet (HNSP and LNSP diet) and ultrasound treatment on particle size distribution and carbon bioavailability in fecal waste of rainbow trout (Oncorynchus mykiss) was studied. Feces were collected from four flow-through fish tanks, two tanks fed the HNSP diet and two the LNSP diet. The collected feces were sonicated (disintegrated) in duplicate with high-intensity (0.6 W/ml), low-frequency (f = 20 Hz) ultrasound at five different energy levels (0.6 W/ml for 0, 0.25, 1, 4, and 16 min). The particle size distribution of the treated feces samples was measured by wet sieving (1000, 500, 200, 100, 63, 36, 1.2 µm screen size) and total suspended solids (TSS) measurement. Carbon bioavailability in sonicated fecal waste samples was determined with oxygen uptake rate (OUR) tests. The results showed that: (1) feces from the HNSP diet contained significant more particulate material and bigger particles; (2) carbon bioavailability was almost three times higher in untreated LNSP feces when compared with HNSP feces; (3) almost 50% of HNSP feces could have been recovered on a microscreen of 36 µm after wet sieving, whereas it was only 10% for LNSP feces; (4) the production of small particles (1.2–36 µm), which could pass a drum filter screen and potentially accumulate in RAS, was approximately 50 g/kg feed, showing no significant differences between diets; (5) sonication increased fecal dry matter below 36 µm (p = 0.015), but it had no significant effect on the median particle size; (6) sonication increased carbon bioavailability with 7–10% for the HNSP feces (p = 0.037); (7) fecal particles withstood up to 16 min sonication at an intensity of 0.6 W/ml and a frequency of 20 Hz corresponding to specific energy input of 20,000 kJ/kg DM without major changes in particle size distribution. The results of this study indicate that the applied ultrasound treatment of fecal waste is not an effective method to increase short-term carbon bioavailability.
    Liver DNA methylation analysis in adult female C57BL/6JxFVB mice following perinatal exposure to bisphenol A
    Esterik, J.C. van; Vitins, A.P. ; Hodemaekers, H.M. ; Kamstra, J.H. ; Legler, J. ; Pennings, J.L.A. ; Steegenga, W.T. ; Lute, C. ; Jelinek, J. ; Issa, J.P. ; Dollé, M.E.T. ; Ven, L.T.M. van der - \ 2015
    Toxicology Letters 232 (2015)1. - ISSN 0378-4274 - p. 293 - 300.
    endocrine disruptors - disease - bpa - xenoestrogens - association - epigenetics - expression - nutrition - evolution - chemicals
    Bisphenol A (BPA) is a compound released from plastics and other consumer products used in everyday life. BPA exposure early in fetal development is proposed to contribute to programming of chronic diseases like obesity and diabetes, by affecting DNA methylation levels. Previously, we showed that in utero and lactational exposure of C57BL/6JxFVB hybrid mice via maternal feed using a dose range of 0–3000 µg/kg body weight/day resulted in a sex-dependent altered metabolic phenotype in offspring at 23 weeks of age. The most univocal effects were observed in females, with reduced body weights and related metabolic effects associated with perinatal BPA exposure. To identify whether the effects of BPA in females are associated with changes in DNA methylation, this was analyzed in liver, which is important in energy homeostasis. Measurement of global DNA methylation did not show any changes. Genome-wide DNA methylation analysis at specific CpG sites in control and 3000 µg/kg body weight/day females with the digital restriction enzyme analysis of methylation (DREAM) assay revealed potential differences, that could, however, not be confirmed by bisulfite pyrosequencing. Overall, we demonstrated that the observed altered metabolic phenotype in female offspring after maternal exposure to BPA was not detectably associated with liver DNA methylation changes. Still, other tissues may be more informative.
    Comparison of aquaculture farming methods for Kenya: FoodTechAfrica
    Kamstra, A. ; Bierbooms, V. ; Aartsen, F. ; Rurangwa, E. ; Eding, E. ; Stokkers, R. ; Duijn, A.P. van - \ 2014
    IJmuiden, Den Haag : IMARES / LEI (Report / IMARES C021/14; 14-035) - 48 p.
    aquacultuur - aquacultuursystemen - kenya - aquaculture - aquaculture systems
    Denitrification on internal carbon sources in RAS is limited by fibers in fecal waste of rainbow trout
    Meriac, A. ; Eding, E.H. ; Kamstra, A. ; Busscher, J.P. ; Schrama, J.W. ; Verreth, J.A.J. - \ 2014
    Aquaculture 434 (2014). - ISSN 0044-8486 - p. 264 - 271.
    recirculating aquaculture systems - single-sludge denitrification - acid-insoluble ash - nitrate removal - digestibility - feed - fish - effluents - digestion - culture
    Denitrification on internal carbon sources offers the advantage to control nitrate levels in recirculating aquaculture systems (RAS) by using the fecal carbon produced within the husbandry system. However, it is not clear to which extent fecal carbon can be utilized by the microbial community within a denitrification reactor. Especially fibers can hamper the bioavailability of carbon in fecal waste. Therefore, this study investigated the nitrogen removal capacity of a denitrification reactor using fecal waste with a high fiber content as the only carbon source in RAS. Furthermore, we investigated to which extent fibers were utilized as a carbon source within the reactor. Four identical small-scale RAS (V = 460 L) were stocked with 25 rainbow trout of ~ 110 g, and operated at a water exchange rate of ~ 200 L/kg of feed DM. Two RAS served as controls without denitrification and two RAS were upgraded with an upflow sludge blanket denitrification reactor (V = 10.5 L). During the six weeks of experiment, we determined COD (chemical oxygen demand, measure for organic carbon) and N balances for all systems and analyzed the composition of the collected solids. The denitrification reactors were able to remove 19 g N/kg of feed DM, or 48% of the metabolic nitrogen waste produced by the fish. Based on the COD balances, 44% of the supplied fecal COD was degraded in the reactor. Hemicellulose and cellulose degradability was ~ 50%, accounting for 45% to the total degraded COD. Under steady state conditions, 4.4 g of biodegradable COD needed to be oxidized to reduce 1 g of nitrogen, indicating respiratory COD losses of approximately 50%. This experiment successfully demonstrated that denitrification on internal carbon sources using a high fiber diet could remove half of the nitrogen waste produced by the fish. Although fibers limited carbon bioavailability, half of the cellulose and hemicellulose present in the fecal waste was utilized in the denitrification reactor.
    Sanitary prescriptions and procedures for transfer and safety standards - aquaexcel (D3.1)
    Afonso, J.M. ; Real, F. ; Padilla, D. ; Kamstra, A. - \ 2014
    Introduction The sanitary prescriptions and procedures for transfer, and safety standards in the framework of the Project "Aquaculture infrastructures for excellence in European fish research (AQUAEXCEL)" of Seventh Framework Programme aims to define the optimum conditions in terms of health and welfare for the transport of fish and/or germplasm by means of regulations for the safe transport between the different research centres of the project members. The sanitary measures featured are based on the standards officially approved by European Legislation, with specific reference to European Directive 2006/88 EC and the World Assembly of Delegates of the OIE. The purpose of this work was to make it easier for the different researchers of the AQUAEXCEL project to draw up sanitary measures applicable to the movement of fish and/or germplasm between the different research centers belonging to the AQUAEXCEL Project. Materials and methods This work (Deliverable 3.1; AquaExcel Project, 2013) includes a description of the main diseases that affect the fish species included in the AQUAEXCEL Project and corresponding methods of diagnosis, paying particular attention to the diseases identified by the research centres in the initial survey, as well as criteria to evaluate harmlessness in the transport of fish and germplasm, the welfare of the farmed fish during transport and the disinfection of eggs. Results The recommendations take into consideration the fish species to be transported and the health status of the country of origin and the research centre in order to avoid the disease to which they are applied being introduced into the research centre or country to which the fish and/or germplasm are transported. These recommendations confer an optimum level of sanitary security to the transport of fish or germplasm among the different research centres participating in the AQUAEXCEL Project. References AquaExcel Project (2013) Deliverable 3.2: Sanitary prescriptions and procedures for transfers and safety standards.
    Effects of reactor scale, ammonium concentration and superficial air speed on nitrification rate in moving bed biofilm reactors
    Kamstra, Andries - \ 2014
    Innovative solution to improve water treatment devices - feed & treat
    Kamstra, Andries - \ 2014
    Assessment of the production capacity of ELCOMEX Aqua Srl
    Kamstra, A. - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR C099/14) - 14
    visteelt - viskwekerijen - tarbot - visproductie - capaciteit - roemenië - fish culture - fish farms - turbot - fish production - capacity - romania
    In this report an estimate is given of the production capacity of the turbot farm of ELCOMEX in Constanta (Romania) based on available literature and a visit to the farm.
    Als goudvis en muntplantje een symbiose aangaan (interview met Andries Kamstra)
    Bouma, K. ; Kamstra, A. ; Vermeulen, T. - \ 2014
    De Volkskrant (2014). - p. 29 - 29.
    Dietary carbohydrate composition can change waste production and biofilter load in recirculating aquaculture systems
    Meriac, A. ; Eding, E.H. ; Schrama, J.W. ; Kamstra, A. ; Verreth, J.A.J. - \ 2014
    Aquaculture 420-421 (2014)15 January 2014. - ISSN 0044-8486 - p. 254 - 261.
    trout oncorhynchus-mykiss - single-sludge denitrification - oreochromis-niloticus l. - rainbow-trout - fish-meal - nile tilapia - nonstarch polysaccharides - salmonid aquaculture - growth-performance - effluent treatment
    This study investigated the effect of dietary carbohydrate composition on the production, recovery and degradability of fecal waste from rainbow trout (Oncorhynchus mykiss) in recirculating aquaculture systems (RAS). Dietary carbohydrate composition was altered by substituting starch with non-starch polysaccharides (NSP) while keeping the diets isonitrogenous and isoenergetic. We tested a high starch, low NSP (LNSP) and a low starch, high NSP (HNSP) diet in six identical, small-scale RAS (V = 460 L). Each diet was tested in three independent systems over a period of six weeks. Shifting dietary carbohydrates from starch to NSPs resulted in a 50% increase in the production of chemical oxygen demand (COD) based on digestibility. Fecal waste recovery showed a 40% increase in HNSP treatments when compared with LNSP. Consequently, the COD output from HNSP systems doubled from 91 g to 194 g of COD per kg feed when compared with LNSP. Although COD production was higher in HNSP systems, the COD load on the biofilters was significantly lower when compared with LNSP systems. COD-to-nitrogen (COD/N) ratios in the biofilter load were 1.7 ± 0.2 and 2.2 ± 0.2 g COD/g N for HNSP and LNSP, respectively. Shifting the dietary carbohydrate composition from starch to NSPs decreased the biodegradability of fecal COD from 66.3% to 43.7% (P <0.001). Fiber analyses revealed that approximately 40% of the COD in HNSP feces came from cellulose and hemicellulose. The increased COD production of HNSP diets could be exploited by using fecal COD as an internal carbon source in denitrification. Full denitrification would be theoretically possible with a measured COD/N ratio of 7.2 in the waste stream of HNSP systems. However, it is not clear if the low COD bioavailability of HNSP feces could be a limiting factor. This study shows that COD/N ratios in the biofilter load and system output can be manipulated by changing dietary carbohydrate composition. Although an increased dietary NSP content increased COD production, it also increased COD recovery, decreased COD load on the biofilters and generated sufficient carbon for denitrification on internal sources.
    The need for systems design for robust aquaponic systems in the urban environment
    Vermeulen, T. ; Kamstra, A. - \ 2013
    In: International Symposium on Soilless Cultivation. - Leuven : ISHS - p. 71 - 77.
    Aquaponics – the co-production of fish and plant products – is gaining interest both by entrepreneurs and researchers. This article evaluates both the technical setup as well as the economic potential of aquaponic systems and is aimed at identifying relevant knowledge questions for further improvements. Using system requirements for hydroponic systems and aquaculture, the aquaponic system was compared to a typical Dutch rockwool system. Aquaponics was found to be an improvement on current practices when using Deep Flow Technique (cultivation in a flowing thick water layer), resulting in better nutrient availability for the plants and re-use of nitrate. However, the technical challenges of the direct linkage between the two production systems in terms of needed technology and disease management was found to make the total system suboptimal when compared to conventional practices. The technological advantages of efficiency in use of land and energy and re-use of nutrients were found to be a marginal cost reduction of 1.2%. The article concludes that the added value of aquaponics can be found in the total business concept of producing in an urban environment with direct relationship with consumers. Further improvement of aquaponics can be found in improved disease management of the system – through management or improved design.
    How do plant protein based diets change COD production and COD/N ratios for denitrification on internal carbon sources in RAS?
    Meriac, A. ; Eding, E.H. ; Kamstra, A. ; Verreth, J.A.J. - \ 2012
    In: AQUA 2012 World Aquaculture Society joint meeting, 1-5 September 2012, Prague, Czech Republic. - - p. 712 - 712.
    Introduction Changing diet composition from fish meal-based protein sources to plant-based protein sources will affect the amount and composition of waste produced in aquaculture operations. Plant-based diets and the inherent increase in fiber content will lead to lower digestibility and an increased production of organic solid waste, measured as chemical oxygen demand (COD). An increase in COD production can be beneficial if COD/N-ratios are limited for denitrification on internal COD sources. Denitrification is a valuable tool to control nitrate, reducing water exchange and nutrient emissions and is often limited by COD availability. However, fibers are generally considered as substrates of low degradability and could be a limiting a factor for denitrification. Current knowledge gaps in this field of research call for a closer investigation of the composition of solid waste, its fiber fractions and the resulting effects on COD/N-ratios and denitrification potential in RAS. Therefore this research assessed the impact of a plant protein-based diet on the production, composition and denitrification potential of the solid COD waste fraction of rainbow trout (Oncorhynchus mykiss) cultured in a RAS. The goal was to determine COD and N mass balance, COD/N ratios and denitrification potential. Material & Methods A 6 week experiment was conducted in 6 identical small-scale conventional RAS (V=450 l), stocked with 25 trout of an initial average body weight of 103 g. The fish were fed a high fiber diet (HF, plant protein based) and a low fiber diet (LF, fish meal based).The two diets were isoenergetic and isonitrogenous based on digestibility and each treatment was replicated three times. The feeding rate was at approximately 1.4 % BW/day. Each RAS was operated at a water exchange rate of 450 l/kg feed. Water quality, fish performance, body composition, waste production, waste recovery and composition of feed and waste was determined. Results & Discussion Water quality was not affected by the treatments, fish growth was 14% lower in LF when compared to HF. Solid COD production and COD/N ratio increased for the HF treatment when compared to the LF treatment (see tab. 1 & fig. 1). This was mainly caused by an increase of the fiber fraction in the waste but as well because of a higher recovery rate in sedimentation. Assuming that 4.4 g of COD are necessary to reduce 1 g NO3-N to N2 (including a biomass yield of 35%), full denitrification on internally generated COD sources in RAS could be theoretically realized with a HF diet when compared to a LF diet. However, if fibers are not degradable, the effective solid COD/N ratios for denitrification would drop to 3.1 and 2.8 g COD/g N/kg feed for HF and LF respectively (see fig. 1). If these predictions are true will be confirmed in bioassays using the collected solid waste samples. The role of fibers as qualitative limitation for COD bioavailability in denitrification still needs investigation.
    How do plant protein based diets change COD production and COD/N ratios for denitrification on internal carbon sources in RAS?
    Meriac, A. ; Eding, E.H. ; Kamstra, A. ; Verreth, J.A.J. - \ 2012
    Introduction Changing diet composition from fish meal-based protein sources to plant-based protein sources will affect the amount and composition of waste produced in aquaculture operations. Plant-based diets and the inherent increase in fiber content will lead to lower digestibility and an increased production of organic solid waste, measured as chemical oxygen demand (COD). An increase in COD production can be beneficial if COD/N-ratios are limited for denitrification on internal COD sources. Denitrification is a valuable tool to control nitrate, reducing water exchange and nutrient emissions and is often limited by COD availability. However, fibers are generally considered as substrates of low degradability and could be a limiting a factor for denitrification. Current knowledge gaps in this field of research call for a closer investigation of the composition of solid waste, its fiber fractions and the resulting effects on COD/N-ratios and denitrification potential in RAS. Therefore this research assessed the impact of a plant protein-based diet on the production, composition and denitrification potential of the solid COD waste fraction of rainbow trout (Oncorhynchus mykiss) cultured in a RAS. The goal was to determine COD and N mass balance, COD/N ratios and denitrification potential. Material & Methods A 6 week experiment was conducted in 6 identical small-scale conventional RAS (V=450 l), stocked with 25 trout of an initial average body weight of 103 g. The fish were fed a high fiber diet (HF, plant protein based) and a low fiber diet (LF, fish meal based).The two diets were isoenergetic and isonitrogenous based on digestibility and each treatment was replicated three times. The feeding rate was at approximately 1.4 % BW/day. Each RAS was operated at a water exchange rate of 450 l/kg feed. Water quality, fish performance, body composition, waste production, waste recovery and composition of feed and waste was determined. Results & Discussion Water quality was not affected by the treatments, fish growth was 14% lower in LF when compared to HF. Solid COD production and COD/N ratio increased for the HF treatment when compared to the LF treatment (see tab. 1 & fig. 1). This was mainly caused by an increase of the fiber fraction in the waste but as well because of a higher recovery rate in sedimentation. Assuming that 4.4 g of COD are necessary to reduce 1 g NO3-N to N2 (including a biomass yield of 35%), full denitrification on internally generated COD sources in RAS could be theoretically realized with a HF diet when compared to a LF diet. However, if fibers are not degradable, the effective solid COD/N ratios for denitrification would drop to 3.1 and 2.8 g COD/g N/kg feed for HF and LF respectively (see fig. 1). If these predictions are true will be confirmed in bioassays using the collected solid waste samples. The role of fibers as qualitative limitation for COD bioavailability in denitrification still needs investigation.
    Technical and economic feasibility of fish culture in Azerbaijan
    Kamstra, A. ; Duijn, A.P. van - \ 2012
    Wageningen UR / LEI / IMARES
    Business opportunities for aquaculture in Ethiopia
    Rothuis, A.J. ; Duijn, A.P. van; Kamstra, A. ; Dejen, E. ; Pijl, W. van der; Rurangwa, E. ; Stokkers, R. - \ 2012
    The Hague : LEI / IMARES (LEI report 2012-003) - ISBN 9789086155798 - 120
    plattelandsontwikkeling - voedselzekerheid - voedselproductie - aquacultuur - bedrijfseconomie - visserij - overheidsbeleid - ethiopië - nederland - rural development - food security - food production - aquaculture - business economics - fisheries - government policy - ethiopia - netherlands
    Biologische tripsbeheersing in prei 2008-2010
    Broek, R.C.F.M. van den; Verstegen, H.A.G. ; Gruppen, R. ; Kamstra, J.H. - \ 2011
    Lelystad : PPO AGV (PPO publicatie 438) - 43
    thrips - biologische bestrijding - insectenplagen - predatoren van schadelijke insecten - plagenbestrijding - preien - akkerranden - compost - roofmijten - bevordering van natuurlijke vijanden - biologische landbouw - thrips - biological control - insect pests - predators of insect pests - pest control - leeks - field margins - composts - predatory mites - encouragement - organic farming
    In diverse vollegrondsgewassen (ui, kool, prei en aardbei) kan trips zowel in gangbare als biologische bedrijven grote problemen opleveren. Trips heeft betrekkelijk weinig natuurlijke vijanden. Vooral roofwantsen komen op trips haarden af en kunnen de populatiegroei afremmen. Rooftrips, roofmijten en spinnen zijn andere, mogelijke natuurlijke vijanden, maar hun belang is grotendeels onbekend. Biologische telers hebben weinig mogelijkheden om tripsen te beheersen. Daarom zijn er in een biologische vollegrondsteelt van prei maatregelen onderzocht die de aanwezige natuurlijke vijanden kunnen stimuleren zoals de aanleg van een bloemenrand, het toedienen van compost en het uitzetten van roofmijten.
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