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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    The complete mitogenome and plastome of the haptophyte Pavlova lutheri NIVA-4/92
    Hulatt, Chris J. ; Wijffels, René H. ; Viswanath, Kiron ; Posewitz, Matthew C. - \ 2020
    Mitochondrial DNA Part B: Resources 5 (2020)3. - ISSN 2380-2359 - p. 2748 - 2749.
    aquaculture - DHA - Haptophyte - lipid metabolism - metabolic model

    The complete mitochondrial and plastid genomes of the microalga Pavlova lutheri strain NIVA-4/92 are reported. The circular-mapping mitogenome is 36,202 bp in length, contains 22 protein-coding genes, 24 tRNAs, and has a GC content of 37.5%. Like other haptophytes the mitogenome contains a single large, complex repeat region of approximately 5.4 kbp. The plastome is 95,281 bp in length and has a GC content of 35.6%. It contains 111 protein-coding genes and 27 tRNAs.

    Swimming Performance and Oxygen Consumption as Non-lethal Indicators of Production Traits in Atlantic Salmon and Gilthead Seabream
    Palstra, Arjan P. ; Kals, Jeroen ; Böhm, Thijs ; Bastiaansen, John W.M. ; Komen, Hans - \ 2020
    Frontiers in Physiology 11 (2020). - ISSN 1664-042X
    aquaculture - feed conversion ratio - metabolic rate - selective breeding - starvation-refeeding - swim-tunnel respirometry

    The aim of this study was to investigate swimming performance and oxygen consumption as non−lethal indicator traits of production parameters in Atlantic salmon Salmo salar L. and Gilthead seabream Sparus aurata L. A total of 34 individual fish of each species were subjected to a series of experiments: (1) a critical swimming speed (Ucrit) test in a swim-gutter, followed by (2) two starvation-refeeding periods of 42 days, and (3) swimming performance experiments coupled to respirometry in swim-tunnels. Ucrit was assessed first to test it as a predictor trait. Starvation-refeeding traits included body weight; feed conversion ratio based on dry matter; residual feed intake; average daily weight gain and loss. Swim-tunnel respirometry provided oxygen consumption in rest and while swimming at the different speeds, optimal swim speed and minimal cost of transport (COT). After experiments, fish were dissected and measured for tissue weights and body composition in terms of dry matter, ash, fat, protein and moist, and energy content. The Ucrit test design was able to provide individual Ucrit values in high throughput manner. The residual Ucrit (RUcrit) should be considered in order to remove the size dependency of swimming performance. Most importantly, RUcrit predicted filet yield in both species. The minimal COT, the oxygen consumption when swimming at Uopt, added predictive value to the seabream model for feed intake.

    Dataset: Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish
    Catalán, Ignacio A. ; Auch, Dominik ; Kamermans, Pauline ; Morales-Nin, Beatriz ; Angelopoulos, Natalie V. ; Reglero, Patricia ; Sandersfeld, Tina ; Peck, Myron A. - \ 2019
    Mediterranean Institute for Advanced Studies (IMEDEA, CSIC-UIB)
    aquaculture - climate change - experiments - fisheries - gap analysis - meta-analysis
    The dataset (Excel) corresponds to the data used to generate the gap analysis of the published paper "Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish" with DOI: 10.1111/faf.12359 It contains 245 cases and 14 variables. The explanation of the variables is contained in the paper.
    Potential of Integrated Mangrove - Shrimp Farming in Bangladesh
    Bosma, Roel - \ 2019
    aquaculture - shrimp - Bangladesh - Mangrove
    Invited key-note speaker for the Trade Delegation at the Bangladesh Embassy, The Hague
    Biogeography of the fish pathogen Aeromonas salmonicida inferred by vapA genotyping
    Gulla, Snorre ; Bayliss, Sion ; Björnsdóttir, Bryndís ; Dalsgaard, Inger ; Haenen, Olga ; Jansson, Eva ; McCarthy, Una ; Scholz, Felix ; Vercauteren, Maaike ; Verner-Jeffreys, David ; Welch, Tim ; Wiklund, Tom ; Colquhoun, Duncan J. - \ 2019
    FEMS Microbiology Letters 366 (2019)7. - ISSN 0378-1097
    Aeromonas salmonicida - aquaculture - bacterial fish pathogen - genotyping - host specificity - vapA/A-layer

    A recently described typing system based on sequence variation in the virulence array protein (vapA) gene, encoding the A-layer surface protein array, allows unambiguous subtyping of Aeromonas salmonicida. In the present study, we compile A-layer typing results from a total of 675 A. salmonicida isolates, recovered over a 59-year period from 50 different fish species in 26 countries. Nine novel A-layer types (15-23) are identified, several of which display a strong predilection towards certain fish hosts, including e.g. Cyprinidae and Pleuronectidae species. Moreover, we find indications that anthropogenic transport of live fish may have aided the near global dissemination of two cyprinid-associated A-layer types. Comparison of whole genome phylogeny and A-layer typing for a subset of strains further resulted in compatible tree topologies, indicating the utility of vapA as a phylogenetic as well as an epizootiological marker in A. salmonicida. A Microreact project (microreact.org/project/r1pcOAx9m) has been created, allowing public access to the vapA analyses and relevant metadata. In sum, the results generated provide valuable insights into the global population structure of A. salmonicida, particularly in relation to its piscine host spectrum and the geographic distribution of these hosts.

    Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish
    Catalán, Ignacio A. ; Auch, Dominik ; Kamermans, Pauline ; Morales-nin, Beatriz ; Angelopoulos, Natalie V. ; Reglero, Patricia ; Sandersfeld, Tina ; Peck, Myron A. - \ 2019
    Fish and Fisheries 20 (2019)3. - ISSN 1467-2960 - p. 501 - 517.
    aquaculture - climate change - experiments - fisheries - gap analysis - meta-analysis
    An amalgam of empirical data from laboratory and field studies is needed to build robust, theoretical models of climate impacts that can provide science-based advice for sustainable management of fish and shellfish resources. Using a semi-systematic literature review, Gap Analysis and multilevel meta-analysis,we assessed the status of empirical knowledge on the direct effects of climate change on 37 high-value species targeted by European fisheries and aquaculture sectors operating in marine and freshwater regions. Knowledge on potential climate change-related drivers (single or combined) on several responses (vital rates) across four categories (exploitation sector, region, life stage, species), was considerably unbalanced as well as biased, including a low number of studies (a) examining the interaction of abiotic factors, (b) offering opportunities to assess local adaptation, (c) targeting lower-value species. The meta-analysisrevealed that projected warming would increase mean growth rates in fishand mollusks and significantly elevate metabolic rates in fish. Decreased levels ofdissolved oxygen depressed rates of growth and metabolism across coherent species groups (e.g., small pelagics, etc.) while expected declines in pH reduced growth in most species groups and increased mortality in bivalves. The meta-analytical results were influenced by the study design and moderators (e.g., life stage, season). Although meta-analytic tools have become increasingly popular, when performed on the limited available data, these analyses cannot grasp relevant population effects, even in species with a long history of study. We recommend actions to overcome these shortcomings and improve mechanistic (cause-and-effect) projections of climate impacts on fish and shellfish.
    A fully integrated simulation model of multi-loop aquaponics : A case study for system sizing in different environments
    Goddek, Simon ; Körner, Oliver - \ 2019
    Agricultural Systems 171 (2019). - ISSN 0308-521X - p. 143 - 154.
    aquaculture - aquaponics - horticulture - hydroponics - integrated multi-trophic aquaculture - systems modelling

    Decoupled multi-loop aquaponics systems separate the recirculated aquaculture system (RAS) and hydroponic (HP) units from each another, creating detached ecosystems with inherent advantages for both plants and fish. This gives the advantage of improved crop and fish cultivation in combination, using the minimum resource input. Up to today, the focus of aquaponics systems is mainly on fish culture and treatment of RAS effluent for optimal use in HP, and systems are designed and sized with rule of thumbs of plant growth, evapotranspiration and nutrient needs, while taking the slow responses of RAS dynamics as basis. However, in order to create the optimal fit between RAS and HP, the different systems and differences in time responses of the underlying process need to be considered. Growth of fish and plants happen in hours or days and are slow processes while photosynthesis and transpiration in crops happen in seconds or minutes and are fast processes. As in a closed loop system the main water use is due to plant transpiration, the necessary sizes of system and sub-system depend on plant transpiration. We therefore aimed at creating an aquaponics-sizing simulator based on deterministic mathematical models and thus transferrable to various circumstances with simple parameterisation. We have combined a full-scale greenhouse simulator with a possible simulation time of min 1 min including HP, greenhouse construction and physics as well as a very detailed plant energy and growth model with a model for a multi-loop aquaponics system including distillation technologies and sumps. To illustrate the quality and wide applicability of our theoretical implementation of a multi-loop aquaponics system in greenhouse conditions we made scenario simulation studies at three different climate zones as sub-arctic cold, moderate and arid subtropical regions (i.e. Faroe Islands [66°N], The Netherlands [52°N], and Namibia [22.6°S]) using the same RAS size while simulating on the fitting HP area. For sizing, we used the element P as the most valuable macronutrient for plants. We simulated in a 1-min time steps for a 3-year duration using hourly input climate data for a complete year. Results clearly indicate the importance of transpiration dynamics on system and sub-system sizing, where e.g. the optimal HP size necessary was 11,250 m 2 , 10,250 m 2 and 5250 m 2 (tomato), or 15,750 m 2 , 14,000 m 2 and 9250 m 2 (lettuce), for Faroe Islands, The Netherlands, and Namibia, respectively.

    Climate change opens new frontiers for marine species in the Arctic: Current trends and future invasion risks
    Chan, Farrah T. ; Stanislawczyk, Keara ; Sneekes, A.C. ; Dvoretsky, Alexander ; Gollasch, Stephan ; Minchin, Dan ; David, Matej ; Jelmert, Anders ; Albretsen, Jon ; Bailey, Sarah A. - \ 2019
    Global Change Biology 25 (2019)1. - ISSN 1354-1013 - p. 25 - 38.
    alien species - aquaculture - climate warming - fisheries - invasion pathways - invasive species - knowledge gap - nonindigenous species - shipping - vessels
    Climate change and increased anthropogenic activities are expected to elevate the potential of introducing nonindigenous species (NIS) into the Arctic. Yet, the knowledge base needed to identify gaps and priorities for NIS research and management is limited. Here, we reviewed primary introduction events to each ecoregion of the marine Arctic realm to identify temporal and spatial patterns, likely source regions of NIS, and the putative introduction pathways. We included 54 introduction events representing 34 unique NIS. The rate of NIS discovery ranged from zero to four species per year between 1960 and 2015. The Iceland Shelf had the greatest number of introduction events (n = 14), followed by the Barents Sea (n = 11), and the Norwegian Sea (n = 11). Sixteen of the 54 introduction records had no known origins. The majority of those with known source regions were attributed to the Northeast Atlantic and the Northwest
    Pacific, 19 and 14 records, respectively. Some introduction events were attributed
    to multiple possible pathways. For these introductions, vessels transferred the greatest number of aquatic NIS (39%) to the Arctic, followed by natural spread (30%) and aquaculture activities (25%). Similar trends were found for introductions attributed to a single pathway. The phyla Arthropoda and Ochrophyta had the highest number of recorded introduction events, with 19 and 12 records, respectively. Recommendations including vector management, horizon scanning, early detection, rapid response, and a pan‐Arctic biodiversity inventory are considered in this paper. Our study provides a comprehensive record of primary introductions of NIS for marine environments in the
    circumpolar Arctic and identifies knowledge gaps and opportunities for NIS research and management. Ecosystems worldwide will face dramatic changes in the coming decades due to global change. Our findings contribute to the knowledge base needed to address two aspects of global change—invasive species and climate change.
    Corrigendum: How Can We Define “Optimal Microbiota?”: A Comparative Review of Structure and Functions of Microbiota of Animals, Fish, and Plants in Agriculture (Frontiers in Nutrition
    Ikeda-Ohtsubo, Wakako ; Brugman, Sylvia ; Warden, Craig H. ; Rebel, Johanna M.J. ; Folkerts, Gert ; Pieterse, Corné M.J. - \ 2018
    Frontiers in Nutrition 5 (2018). - ISSN 2296-861X
    agricultural immunology - agriculture - animal husbandry - aquaculture - microbiota - phyllosphere - rhizosphere

    In the original article, we regret that the following Funding statement was missing: This work was financially supported by the Japan Society for the Promotion of Science (JSPS) through JSPS Core-to-Core Program (Advanced Research Networks) entitled Establishment of international agricultural immunology research-core for a quantum improvement in food safety. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

    Geert Wiegertjes, hoogleraar Visteelt en Visserij in Wageningen, houdt van karpers en driehoeken
    Wiegertjes, G. ; Veld, M. ter - \ 2018
    animal welfare - animal production - aquaculture - fishes - animal experiments - animal health
    The effect of low pH on physiology, stress status and growth performance of turbot (Psetta maxima L.) cultured in recirculating aquaculture systems
    Mota, Vasco C. ; Hop, Jochem ; Sampaio, Luís A. ; Heinsbroek, Leon T.N. ; Verdegem, Marc C.J. ; Eding, Ep H. ; Verreth, Johan A.J. - \ 2018
    Aquaculture Research 49 (2018)10. - ISSN 1355-557X - p. 3456 - 3467.
    aquaculture - fish - NH-N - nitrification - total ammonia nitrogen (TAN)

    We evaluated the effect of low pH and low and high total ammonia nitrogen (TAN) concentrations on the physiology, stress status and the growth performance of turbot in RAS. Two experiments were conducted. In Experiment 1, turbot (466 g) were grown at control (pH 7.5; TAN ~0.5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 55 days. In Experiment 2, turbot (376 g) were grown at control (pH 7.5; TAN ~0.5 mg/L), low pH and low TAN (pH 5.7; TAN ~5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 59 days. In Experiment 1, final body weight, feed intake and growth were significantly lower and FCR significantly higher in turbot exposed to low pH and high TAN. In Experiment 2, only growth was significantly lower in turbot exposed to treatment low pH and high TAN as compared to fish in the control treatment and low pH and low TAN. Osmoregulation and stress indicators measured were within normal levels. In conclusion, turbot grew equally well in a water pH of 7.5 or 5.7 provided a low TAN. In contrast, low pH combined with a high TAN impaired turbot performance.

    Cyanobacterial Blooms and Microcystins in Southern Vietnam
    Trung, Bui ; Dao, Thanh Son ; Faassen, Els ; Lürling, Miquel - \ 2018
    Toxins 10 (2018)11. - ISSN 2072-6651
    aquaculture - cyanobacteria - cyanotoxins - Mekong river

    Studies on cyanobacteria in Vietnam are limited and mainly restricted to large reservoirs. Cyanobacterial blooms in small water bodies may pose a health risk to local people. We sampled 17 water bodies in the vicinity of urban settlements throughout the Mekong basin and in southeast Vietnam. From these, 40 water samples were taken, 24 cyanobacterial strains were isolated and 129 fish, 68 snail, 7 shrimp, 4 clam, and 4 duck samples were analyzed for microcystins (MCs). MCs were detected up to 11,039 µg/L or to 4033 µg/g DW in water samples. MCs were detected in the viscera of the animals. MC-LR and MC-RR were most frequently detected, while MC-dmLR, MC-LW, and MC-LF were first recorded in Vietnam. Microcystis was the main potential toxin producer and the most common bloom-forming species. A potential health hazard was found in a duck⁻fish pond located in the catchment of DauTieng reservoir and in the DongNai river where raw water was collected for DongNai waterwork. The whole viscera of fish and snails must be completely removed during food processing. Cyanobacterial monitoring programs should be established to assess and minimize potential public health risks.

    The Shifting Politics of Sustainable Seafood Consumerism
    Bush, S.R. ; Roheim, C.A. - \ 2018
    In: The Oxford Handbook of Political Consumerism / Boström, Magnus, Micheletti, Michele, Oosterveer, Peter, Oxford University Press (Oxford Handbook Online ) - ISBN 9780190629038 - 22 p.
    fisheries - aquaculture - environment - governance - value chains - social movements
    Seafood has emerged as a key testing ground for understanding the role of different value chain actors in driving sustainability. The conventional view, developed in the late 1990s, is that sustainable seafood is driven by the choices and practices of consumers in major importing markets, such as the United States and the European Union. This view led to the development of a range of boycott and buycott initiatives in the 2000s. Many of the buycott initiatives have been formalised into consumer-facing tools, such as certification, recommendation lists, and traceability. More recently celebrity chefs have also joined in, shaping sustainable seafood as cuisine. While these initiatives and tools initially assumed a demand-shapes-supply mode of political consumerism, they have all
    broadened to include multiple modes of political consumerism. The future of the
    sustainable seafood movement is therefore dependent on a clearer articulation of diverse modes of political consumerism.
    Perceived versus real toxicological safety of pangasius catfish: a review modifying market perspectives
    Murk, Albertinka J. ; Rietjens, I.M.C.M. ; Bush, S.R. - \ 2018
    Reviews in Aquaculture 10 (2018)1. - ISSN 1753-5123 - p. 123 - 134.
    aquaculture - mass media - pangasius (Pangasianodon hypophthalmus - safety assessment - seafood quality - toxic compounds
    Mass media reports suggest that pangasius (Pangasianodon hypophthalmus) is ‘full of poison’ because it is able to survive in the ‘heavily polluted Mekong River’ and contains pesticides and veterinary treatment chemicals. However, most of these claims are not substantiated with scientific evidence. To assess the safety of pangasius consumption, a full toxicological risk assessment was performed. The results obtained were compared to toxicity claims made in a selection of media reports. Information on contaminant levels encountered in pangasius was collected from the EU Rapid Alert System for Food and Feed (RASFF) database. The toxicological risk assessments do not support any of the toxicological risks suggested in the media. Next, the maximum pangasius consumption that would be considered safe was estimated on the basis of the highest levels of the toxic contaminants reported in Vietnamese pangasius by RASFF and the safety thresholds for the contaminants. The maximum amount of the recalled fillet that could have been consumed without any adverse effects amounted to between 3.4 and 166.7 kg day−1 (lifelong for a 70 kg adult) in the case of pesticide contamination and between 0.613 and 303 kg fillet day−1 in the case of preservatives and antibiotics. It is concluded that consumption of pangasius available on the European market does not pose any concern for the health of the consumer. The analysis presented in this study illustrates that publicly available independent information could help consumers to develop their own well-informed opinion about food safety issues.
    Investing in climate change mitigation and adaptation on mangrove and aquaculture doubles benefits
    Bosma, R.H. ; Hakim, Lugas Lukmanul ; Groeneveld, R.A. - \ 2017
    - 1 p.
    aquaculture - mangrove recovery - abrasion - investment - climate change
    The evaluation of energy in fish feed
    Haidar, Mahmoud - \ 2017
    Wageningen University. Promotor(en): J.A.J. Verreth, co-promotor(en): J.W. Schrama. - Wageningen : Wageningen University - ISBN 9789463438049 - 155
    oreochromis niloticus - fish feeding - feed formulation - digestible energy - dietary protein - dietary fat - carbohydrates - growth - feed evaluation - fish culture - aquaculture - oreochromis niloticus - visvoeding - voersamenstelling - verteerbare energie - voedingseiwit - voedingsvet - koolhydraten - groei - voederwaardering - visteelt - aquacultuur

    New and alternative plant ingredients are increasingly incorporated in fish feed due to the scarcity of captured fish and increased fishmeal and fish oil prices. As a result, current fish feeds are characterized by a highly variable ingredients composition, leading to a similar variability in the dietary macronutrients composition, especially the carbohydrates fraction. Appropriate formulation of the energy component in fish feeds requires information on nutrient digestibility, energy requirements for maintenance, and the efficiency of utilization of digestible energy for growth (kgDE). In fish feed formulation, the energy evaluation is based on digestible energy (DE) basis. The main assumptions of this DE system are that maintenance requirements and kgDE are independent of dietary factors. The main objective of this thesis was to evaluate and improve the DE system for Nile tilapia. Data showed that, opposite to what is assumed in literature and irrespective of the feeding level applied, an optimal digestible protein to digestible energy ratio (DP/DE) for young Nile tilapia could not be detected. In addition, it was expected that Nile tilapia would show a maximal protein deposition in relation to a wide range of DP/DE ratios, however, this was either observed. Further investigations showed that different body compartments/organs responded differently in terms of protein and fat composition as a result of changes in the dietary DP/DE ratio. In tilapia, viscera and the “rest” fraction (head, skin, fins and bones) were the main site for fat retention. In addition, protein content of fillets seems to be constant (about 17%) and not affected by dietary factors in Nile tilapia. In addition, the effect of using new plant ingredients in Nile tilapia diets was also investigated. The results showed that the ingredients composition had an effect on the maintenance requirements of Nile tilapia. Further, changes in the ratio of starch vs non starch carbohydrates revealed that energy retention was lower when more dietary fibers were included. In addition, the net energy retention differed also when the levels of digestible protein, fat and carbohydrates changed in the diets. The latter results proved that kgDE was not constant and was dependent on diet composition. All aforementioned results led us to calculate the energetic efficiencies of digestible protein, fat and carbohydrates for net energy retention. These estimated efficiencies were used to propose a net energy evaluation system being feasible for Nile tilapia.

    AQUAFARM van zuiveren naar oogsten
    Verdonschot, P.F.M. - \ 2017
    Aquafarm NL
    afvalwater - waterzuivering - industriële grondstoffen - biobased economy - afvalwaterbehandeling - aquacultuur - biomassa productie - waste water - water treatment - feedstocks - biobased economy - waste water treatment - aquaculture - biomass production
    Aquafarm ziet afvalwater als basis voor het produceren van hoogwaardige bouwstoffen, waarmee tegelijkertijd het water gezuiverd wordt.
    The development of a sole diet based on the composition of ragworm
    Kals, Jeroen - \ 2017
    Wageningen University. Promotor(en): J.A.J. Verreth, co-promotor(en): J.W. Schrama; R.J.W. Blonk. - Wageningen : Wageningen University - ISBN 9789463431804 - 136
    dover soles - annelida - fish feeding - anaemia - haemoglobin - fish culture - aquaculture - tong (vis) - annelida - visvoeding - anemie - hemoglobine - visteelt - aquacultuur

    Scientifically, this study aimed to validate the potential of ragworm to alleviate anaemia in common sole and to identify the dietary requirements of common sole to alleviate this anaemia. At the same time it was aimed to explain part of the difference in growth between sole fed a commercial pellet and sole fed ragworm. Practically, this study aimed to develop a diet that achieves similar growth rates in sole as when fed ragworm. Sole fed commercial pellets developed nutritional anaemia. Feeding ragworm or mussel alleviates this nutritional anaemia. It is suggested that the ability of mussel or ragworm (meal) to alleviate anaemia and improve growth in sole can be explained by heme iron and high B12 levels. Yet, iron absorption in sole is high and independent of iron source. Still, heme increases the absorption of copper. The high absorption of iron and copper in sole fed heme does not affect the haematocrit (Hct) and haemoglobin (Hb) levels, which indicates the anaemia in sole is not an iron or a copper deficiency anaemia. The Hct and Hb levels in sole are affected by dietary B12. Yet, the applied levels are unable to alleviate the anaemia in sole induced by feeding commercial pellets. More options to alleviate the nutritional anaemia in common sole are discussed. Nutrients as vitamin C, B1, B2, B5 and a possible role of dietary EPO are discussed. It is suggested that the slow growth of pellet-fed sole might be due to the low Hct and Hb levels, which hampers the uptake of oxygen, and thus also the overall metabolic capacity, including the scope for growth. Discussed is a 7°C difference in the “optimal” temperature between sole fed ragworm and the 2nd generation pellet and that the “worm effect” is dependent on temperature. However, the growth rate of sole fed the 3rd generation pellet at 18.4°C was comparable to the growth rate of sole fed ragworm, which could not have been the consequence of increasing Hct and Hb levels as these were comparable to levels found in sole fed commercial pellets. Yet, B12 levels in blood plasma of sole are up to 200 times those of other (fish) species. Hence, we inferred on the possibility of a specific metabolic function of B12 in respiration in sole. In addition, the economic and practical impact of the improved growth rate in sole culture is discussed. Finally, several suggestions for future research are given.

    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.

    Mission report Kenya : scoping Mission Marine Fisheries Kenya
    Hoof, Luc van; Steins, Nathalie A. - \ 2017
    IJmuiden : Wageningen Marine Research (Wageningen Marine Research report C038/17) - 136
    marine fisheries - food security - aquaculture - seaweeds - trade - kenya - zeevisserij - voedselzekerheid - aquacultuur - zeewieren - handel - kenya
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