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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    Quantifying methionine requirement of juvenile African catfish (Clarias gariepinus)
    Elesho, F.E. ; Sutter, D.A.H. ; Swinkels, M.A.C. ; Verreth, J.A.J. ; Kröckel, S. ; Schrama, J.W. - \ 2021
    Aquaculture 532 (2021). - ISSN 0044-8486
    African catfish - Amino acid - Digestible methionine - Digestible protein - Requirement
    This study was conducted to estimate the methionine (Met) requirement of African Catfish (Clarias gariepinus). A basal diet was formulated to contain 32% crude protein, 12% lipids, and 0.44% cysteine using only protein from legume ingredients as intact protein. This diet was supplemented with graded levels of crystalline DL- methionine (0, 0.12, 0.24, 0.36, 0.48, 0.60, and 0.84%), which resulted in seven dietary methionine levels ranging from 12.2 to 36.0 g kg−1 crude protein. Triplicate groups of 40 fish (78 g) were restrictively fed one of the seven diets for six weeks. Dietary methionine level significantly affected growth rate, feed conversion ratio, retained nitrogen, methionine efficiency and body composition. All parameters were fitted to dietary digestible methionine content expressed per unit of digestible protein (dMetDP) to estimate the Met requirement using; the linear plateau model (LP), broken line model (BL), or quadratic regression model (QR). LP and BL recorded similar values for requirement estimates while QR evidently recorded a 57% higher requirement estimates across different parameters. The digestible methionine requirement of African catfish for growth (using LP) ranges between 18.7 and 21.4 g kg−1 per unit of digestible protein. This equates to a minimum dietary methionine level of 6.3 g kg−1 diet (19.2 g kg−1 Crude protein), which is lower than was has been previously reported for this species.
    30 years of large river restoration: How long do restored floodplain channels remain suitable for targeted rheophilic fishes in the lower river Rhine?
    Stoffers, T. ; Collas, F.P.I. ; Buijse, A.D. ; Geerling, G.W. ; Jans, L.H. ; Kessel, N. Van; Verreth, J.A.J. ; Nagelkerke, L.A.J. - \ 2020
    Science of the Total Environment (2020). - ISSN 0048-9697
    The ecological efficacy of river restoration projects may change over time, resulting in the loss of their ecological function for targeted species. The goal of this study was to evaluate the rheophilic nursery function of restored floodplain channels over time, by analysing 30 years of monitoring data from 12 restoration projects in the lower river Rhine. We hypothesised that the nursery function would change over time, caused by the combined effects of decreasing flow conditions and succession processes affecting habitat heterogeneity. We found that nursery area suitability for rheophilic fish was almost 4 times higher in two-sided connected channels than in one-sided connected channels, although the response trends of rheophilic fish were similar for both water body types. These response curves showed clear optima with channel age, for rheophilic fish abundance at 13 to 14 years post-restoration, indicating optimal nursery conditions. On the other hand, rheophilic species richness showed a steadily decreasing trend with channel age, suggesting aging channels became less suitable as nursery areas for most rheophilic fish species. The presence of permanent flow was found to be the main driving factor in explaining both rheophilic fish community trends and habitat succession in individual restored channels. We did not observe an effect of habitat heterogeneity on nursery function for rheophilic fish. To create and maintain optimal nursery conditions in restored floodplain channels of strongly anthropogenically influenced rivers such as the river Rhine, we propose a management strategy involving cyclic rejuvenation through human intervention, focusing on restoring permanent flow, with a frequency of on average every 15 years, depending on the rate of aggradation and targeted rheophilic species. We also propose a thorough investigation of the relationship between habitat heterogeneity and nursery success in floodplain channels, as a next step in the identification of suitable nursery areas for rheophilic fishes.
    Doses response of dietary viscosity on digestibility and faecal characteristics of striped catfish (Pangasionodon hypophthalmus)
    Tu-Tran, L.C. ; Nguyen, Thanh Cong ; Verreth, Johan A.J. ; Schrama, Johan W. - \ 2020
    Aquaculture Research 51 (2020)2. - ISSN 1355-557X - p. 595 - 604.
    digestibility - faecal waste - guar gum - striped catfish

    The study analysed the dose–response relationship between dietary viscosity and nutrient digestibility, faecal waste characteristics in striped catfish and the long-term impacts of viscosity on performance of striped catfish. This was done in two experiments: Exp.1 lasted 29 days, in which six dietary viscosity levels were created by including different amount of guar gum (GG; 0, 0.25, 0.5, 1.0, 2.0 or 3.0 g/kg) and Exp.2 lasted 60 days and assessed the long-term effects of three dietary GG levels (0, 0.5 and 3.0 g/kg) were checked. In Exp.1, digestibility of nutrients (except crude fat) decreased linearly with dietary viscosity. With increasing viscosity, removal efficiency of faeces from the water reduced linearly, whereas the total amount of faeces produced and the fraction of big-sized faecal particles (>2 mm). increased linearly. In Exp.1, viscosity did not affect performance. However, in Exp.2, the GG inclusion level of 3.0 g/kg (1.72 cP for the viscosity) affected fish performance. In conclusion, the best strategy for faecal waste management in striped catfish by dietary viscosity is to keep it as low as possible in the diet.

    Integration of Algae to Improve Nitrogenous Waste Management in Recirculating Aquaculture Systems : A Review
    Ramli, Norulhuda Mohamed ; Verreth, J.A.J. ; Yusoff, Fatimah M. ; Nurulhuda, K. ; Nagao, N. ; Verdegem, Marc C.J. - \ 2020
    Frontiers in Bioengineering and Biotechnology 8 (2020). - ISSN 2296-4185
    algal cultivation - ammonia - HRT - nitrate - nitrogen - recirculating aquaculture system - removal rates

    This review investigates the performance and the feasibility of the integration of an algal reactor in recirculating aquaculture systems (RAS). The number of studies related to this topic is limited, despite the apparent benefit of algae that can assimilate part of the inorganic waste in RAS. We identified two major challenges related to algal integration in RAS: first, the practical feasibility for improving nitrogen removal performance by algae in RAS; second, the economic feasibility of integrating an algal reactor in RAS. The main factors that determine high algal nitrogen removal rates are light and hydraulic retention time (HRT). Besides these factors, nitrogen-loading rates and RAS configuration could be important to ensure algal performance in nitrogen removal. Since nitrogen removal rate by algae is determined by HRT, this will affect the size (area or volume) of the algal reactor due to the time required for nutrient uptake by algae and large surface area needed to capture enough light. Constraints related to design, space, light capture, and reactor management could incur additional cost for aquaculture production. However, the increased purification of RAS wastewater could reduce the cost of water discharge in places where this is subject to levees. We believe that an improved understanding of how to manage the algal reactor and technological advancement of culturing algae, such as improved algal reactor design and low-cost artificial light, will increase the practical and economic feasibility of algal integration in RAS, thus improving the potential of mass cultivation of algae in RAS.

    Data from: 30 years of large river restoration: how long do restored floodplain channels remain suitable for targeted rheophilic fishes in the lower river Rhine?
    Stoffers, Twan ; Collas, Frank ; Buijse, A.D. ; Geerling, G.W. ; Jans, L.H. ; Kessel, Nils Van; Verreth, Johan ; Nagelkerke, Leo - \ 2020
    Wageningen University & Research
    river rehabilitation - habitat succession - nursery area - riverine fishes - river management - cyclic rejuvenation
    The ecological efficacy of river restoration projects may change over time, resulting in the loss of their ecological function for targeted species. The goal of this study was to evaluate the rheophilic nursery function of restored floodplain channels over time, by analysing 30 years of monitoring data from 12 restoration projects in the lower river Rhine.
    Effects of carbohydrate sources on a biofloc nursery system for whiteleg shrimp (Litopenaeus vannamei)
    Tinh, Tran Huu ; Koppenol, Tom ; Hai, Tran Ngoc ; Verreth, Johan A.J. ; Verdegem, Marc C.J. - \ 2020
    Aquaculture 531 (2020). - ISSN 0044-8486
    Biofloc - Corn starch - Diurnal fluctuation - Molasses - Nutrient accumulation

    In biofloc technology carbohydrate is added to stimulate the biofloc growth, the latter helps to improve water quality, reduce the need for water exchange and may serve as natural shrimp feed. The large diversity among possible carbohydrate sources makes the selection of a suitable carbohydrate difficult. This study investigated how corn starch addition compared to molasses addition affected water quality, biofloc and periphyton proximate composition, shrimp production parameters, diurnal fluctuations and distribution of carbon and nitrogen in whiteleg shrimp (Litopenaeus vannamei) culture system. The results showed that both corn starch and molasses addition treatments resulted in low ammonium nitrogen levels in the water. The total suspended solids and volatile suspended solids in both treatments increased over time and were not significantly different among treatments. The protein content in the dry matter of the biofloc varied from 34% to 48%, being higher in the molasses treatment. The same was observed for the protein content in the dry matter of the periphyton which ranged between 16% and 26%. The corn starch treatment resulted in significantly higher shrimp growth rate, production, average body weight, and lower FCR compared to molasses addition. Water quality was stable on a daily basis, but changed over the weeks. Carbon and nitrogen accumulations in the system were not significantly different among treatments.

    Effect of feeding during off-flavour depuration on geosmin excretion by Nile tilapia (Oreochromis niloticus)
    Schram, Edward ; Kwadijk, Christiaan ; Hofman, Angelo ; Blanco, Ainhoa ; Murk, Albertinka ; Verreth, Johan ; Schrama, Johan - \ 2020
    Aquaculture 531 (2020). - ISSN 0044-8486
    Blood lipid - Feeding - Geosmin - Nile tilapia - Off-flavour depuration

    The effect of feeding during off-flavour depuration on the elimination of geosmin from muscle tissue (fillet) and ovaries as a model for caviar was assessed in Nile tilapia (Oreochromis niloticus) (mean ± SD weight of 185 ± 15.0 g). The experiment had a 2 × 4 factorial design with feeding level (starved or fed) and depuration time (24, 48, 72 and 96 h) as factors with duplicates for each of the 8 treatment combinations. Fish were normally loaded with geosmin prior to the experiment. During off-flavour depuration geosmin levels in fillet and ovary declined over time in both fed and starved tilapia. In fed tilapia geosmin declined faster from the ovaries compared to starved fish (p = 0.018). The same trend of a faster decline was observed for the muscle tissue (fillets) of fed tilapia, though only numerically (p = 0.11). Because faster geosmin elimination paralleled with high blood lipids, we do not rule out that blood lipids are involved in geosmin transport via the circulatory system and that low blood lipid levels are limiting geosmin elimination in starved fish. No difference in geosmin elimination rate was detected between ovary and muscle tissue in Nile tilapia. Off-flavour depuration time is strongly reduced when farmers adopt a practice of feeding Nile tilapia during off-flavour depuration.

    Dietary non-starch polysaccharides influenced natural food web and fish production in semi-intensive pond culture of Nile tilapia
    Kabir, K.A. ; Verdegem, M.C.J. ; Verreth, J.A.J. ; Phillips, M.J. ; Schrama, J.W. - \ 2020
    Aquaculture 528 (2020). - ISSN 0044-8486
    ADC - Cellulose - Lignin - Pectin - Stable isotope

    Dietary non-starch polysaccharides (NSP) changes the nutrient digestibility and faecal characteristics in fish. This study assessed the effect of the type of dietary NSPs on fish production and the contribution of natural food to the total fish production in semi-intensively managed tilapia ponds. Twelve ponds, each divided into three equally-sized compartments, were assigned to test the effect of the type of dietary NSPs (i.e. “PecHem-Diet”, a diet with easily fermentable NSP, vs “LigCel-Diet”, a diet with slowly fermentable NSP). Fish were restrictively fed, based on the crude protein content of the feed. Three feeding levels (“no = 0”, “low = 9 g.kg-0.8.d−1” and “high= 18 g.kg-0.8.d-1”) nested in pond were analysed in a split plot design. Initial fish biomass was 3084 g.compartment−1 and the experiment lasted 56 days. With the “LigCel-Diet” biomass gain was higher (2599 vs 2192 g.compartment−1) and feed conversion ratio (FCR) was lower (1.4 vs 1.9; P < .001) than with the “PecHem-Diet”. Diet had no effect on fish survival and specific growth rate (SGR). For both diets, increasing feeding level increased (P < .001) biomass gain, fish survival, FCR and SGR. There was a significant interaction effect (P < .05) between diet and feeding level on FCR. Fish body composition was the same in both diets. With the “LigCel-Diet”, the apparent digestibility coefficient (ADC) was higher (P < .001) for crude protein, fat, phosphorus and calcium and lower (P < .05) for ash compared to the other diet. Neither feeding level nor the interaction between diet and feeding level influenced the apparent digestibility coefficient (ADC) of any nutrient. Diet composition did not alter the organic matter (OM) composition of the faeces. δ13C and δ15N from the stable isotope analysis revealed that N gain in fish originated from both feed and natural food of the pond. Natural food abundance in the pond increased over time for both diets. Chlorophyll-a was higher in the pond fed with “LigCel-Diet”. Fish gut content and calculated N gain indicated an enhanced contribution of natural food to fish growth in ponds fed with “LigCel-Diet”. In conclusion, the type of dietary NSP determines tilapia productivity in semi-intensive managed ponds by altering food web productivity.

    Quantifying methionine requirement of African catfish (clarias gariepinus) using a plant-based diet
    Elesho, Folasade ; Verreth, J.A.J. ; Sutter, D.A.H. ; Kröckel, S. ; Schrama, J.W. - \ 2020
    In: Wias Annual Conference 2020 WIAS - p. 65 - 65.
    The increasingly use of plant ingredients to replace high cost fishmeal has motivated fish nutritionist to investigate the amino acid (AA) profile and their individual requirements in commonly cultured species. Problems associated with the use of plant ingredients include the presence of anti-nutritional factors and AA deficiencies. Methionine is the first limiting AA in most leguminous plants. It is a sulphur-containing essential amino acid that is required for the synthesis of cysteine in animal and humans. Methionine is an initiation codon required during protein synthesis for protein formation. Inclusion levels of methionine below the requirements may cause growth reduction and decrease feed efficiency in fish. Therefore,adequate supply of methionine is essential in fish diets. Methionine requirements have been determined for several fish species, however, no reliable information is currently available for African catfish (Clarias gariepinus). Therefore, a 7-week experiment was conducted to estimate the dietary methionine requirement of juvenile African catfish (initial weight78 g), reared in a recirculation aquaculture system. A low-methionine (plant-based) dietwas formulated using soy protein concentrate and faba beans as intact protein. Based onthe methionine requirements for other species, which was obtained from literature, 7 diets were formulated, which all had the same basal composition but supplemented with different amount of crystalline DL-methionine: 0, 0.12, 0.24, 0.36, 0.48, 0.60, and 0.84%. Fish werefed restrictively twice a day at 90% satiation. Apparent digestibility coefficient (ADC) ofnutrients were measured by using settling tanks connected to the outlet of the aquaria in which African catfish were housed. The body composition of the fish were analysed both at the start and end of the experiment to determine the amino acid deposition, energy and nitrogen balance. At the end of the experiment, fish were weighed to determine the final body weight. Broken-line regression analysis was used to determine the quantitative methionine requirement by estimating the break-point for retained nitrogen and growth.The break point of the growth response curve occurred at 6.01 g methionine /kg diet. The reported methionine requirement value in this study can be used to formulate least cost -diets using plants ingredients for production of African catfish.
    Effect of dietary carbohydrate to lipid ratio on performance of Nile tilapia and enhancement of natural food in pond aquaculture
    Kabir, Kazi A. ; Verdegem, Marc C.J. ; Verreth, Johan A.J. ; Phillips, Michael J. ; Schrama, Johan W. - \ 2020
    Aquaculture Research 51 (2020)5. - ISSN 1355-557X - p. 1942 - 1954.
    CHO - LIP ratio - natural food - non-protein energy - pond

    This study tested the effect of two diets differing in carbohydrate to lipid (CHO:LIP) ratio (4.7 vs. 19.5 g/g) on the contribution of natural food and the total fish production in tilapia ponds. Eight ponds, each divided into three equally sized compartments, were assigned to one of the two diets, which differed in CHO:LIP ratio but had the same digestible protein to digestible energy (DP:DE) ratio (15.5 and 15.6 g/MJ). Ponds were fed equal amounts of crude protein. Three feeding levels (no, low and high) were nested in each pond in a split plot design. Average body weight of fish at stocking was 90 g, and the duration of the experiment was 42 days. Increasing the CHO:LIP ratio had no impact on tilapia production. However, the feeding level influenced both biomass gain, specific growth rate and survival. The apparent digestibility coefficient (ADC) for fat and carbohydrate was influenced by dietary CHO:LIP ratio but ADC for energy was unaffected. Proximate analysis of fish body composition showed no effect of diet except for levels of ash. Diet had no effect on the organic matter composition of the faeces, and the contribution of natural food to fish nitrogen gain. Therefore, we postulate that changing the dietary non-protein energy source from lipid to carbohydrate does not have any impact on tilapia culture in semi-intensive ponds.

    The effect of gas to liquid ratio on carbon dioxide removal and heat loss across a forced ventilated trickling filter
    Karimi, Davood ; Eding, Ep ; Aarnink, Andre J.A. ; Groot Koerkamp, Peter ; Verreth, Johan - \ 2020
    Aquacultural Engineering 88 (2020). - ISSN 0144-8609
    Carbon dioxide stripping - Degassing - Energy - Forced ventilation - Gas:Liquid ratio (GLR) - Heat - Nitrification - RAS - Trickling filter (TF)

    The objective of this study was to investigate the effect of the gas: liquid ratio (GLR) on carbon dioxide removal and heat loss across a forced-ventilated trickling filter (TF) used as bioreactor. The effect of 8 different GLRs (1.2–15.7) on carbon dioxide removal and heat loss from water passing a trickling filter were tested in random order. The TF was part of a pilot scale fresh water intensive recirculating aquaculture system and had a media bed height of 1.8 m, a diameter of 0.9 m, a specific surface area of 200 m2/m3 and was operated at a fixed hydraulic surface load of 9.42 m3/m2.h, a mean inlet water temperature of 27.0–27.5 °C, and a mean inlet pH ranging from 7.02–7.12. For each GLR, CO2 removal from water was calculated from CO2 measurements in the inlet and outlet air of the TF using an online infrared probe (developed for agriculture and greenhouses) and from 12 water measurements done once every 3 h during 2 subsequent days. The water inlet CO2 concentrations varied between 4.5–9.0 mg/L (calculated from total inorganic carbon and pH). The results showed that the CO2 removal from water to the air in a trickling filter increased from 3.1 mg/L at a GLR of 1 to 6.1 mg/L for a GLR of 15. The relationship between GLR and CO2 removal could be described as an asymptotic curve with the following equation [Formula presented]; (R2 = 0.91). A linear relation between total heat loss across the TF and the applied GLRs showed an average total heat loss of 33.2 kJ per cubic meter of air for all GLRs. Of the total heat loss on average 91 % was latent heat loss and 9 % sensible heat loss. This study showed that: (1) GLRs above 5 will not result in significant additional CO2 removal; (2) energy loss at a GLR of 5 is, under our experimental conditions with a mean inlet air temperature of 22.6 °C and an mean inlet air relative humidity of 66.9 %, 26.0 kJ per g CO2 removed.

    The effect of dietary protein to energy ratio and stocking densities on fish production, food web enhancement and economic benefit of gift Nile tilapia aquaculture in ponds
    Kabir, K.A. ; Verdegem, M.C.J. ; Schrama, J.W. ; Verreth, J.A.J. ; Phillips, Michael J. - \ 2019
    In: Book of abstracts of the 12th Asian Fisheries & Aquaculture Forum (AFAF). - - p. 315 - 315.
    In non-lined ponds, natural food complements dietary P/E. We assessed the effect of lowering dietary PIE ratio with an increasing stocking density on performance of tilapia, food web enhancement and impact on pond nutrients. The experiment was conducted in a 2x2x2 factorial design: diet (CP:CE ratio 19 vs. 14 g.MJ-1); feeding level; and stocking density (2 vs 3 m-2) in 40 farmers' ponds. Biomass gain increased with a decreasing dietary PIE ratio and increasing stocking density). A negative accumulation of N and P in pond water was noticed for low stocking density ponds. Nitrogen gain in fish was higher for low P/E diet and also influenced by feed per square meter. At low P/E diet, the contribution of natural food to fish production was higher than for the high P/E diet. Net profit increased by lowering the dietary P/E ratio of the diet (2070 vs 1072 US$ ha-1 83 day-1).
    The effect of dietary protein to energy ratio and stocking densities on fish production, food web enhancement and economic benefit of gift Nile tilapia aquaculture in ponds
    Kabir, Kazi ; Verdegem, Marc ; Schrama, Johan ; Verreth, Johan ; Phillips, Michael J. - \ 2019
    In non-lined ponds, natural food complements dietary P/E. We assessed the effect of lowering dietary PIE ratio with an increasing stocking density on performance of tilapia, food web enhancement and impact on pond nutrients. The experiment was conducted in a 2x2x2 factorial design: diet (CP:CE ratio 19 vs. 14 g.MJ-1); feeding level; and stocking density (2 vs 3 m-2) in 40 farmers' ponds. Biomass gain increased with a decreasing dietary PIE ratio and increasing stocking density). A negative accumulation of N and P in pond water was noticed for low stocking density ponds. Nitrogen gain in fish was higher for low P/E diet and also influenced by feed per square meter. At low P/E diet, the contribution of natural food to fish production was higher than for the high P/E diet. Net profit increased by lowering the dietary P/E ratio of the diet (2070 vs 1072 US$ ha-1 83 day-1).
    Options to reuse sludge from striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878) ponds and recirculating systems
    Nhut, N. ; Hao, N.V. ; Bosma, R.H. ; Verreth, J.A.V. ; Eding, E.H. ; Verdegem, M.C.J. - \ 2019
    Aquacultural Engineering 87 (2019). - ISSN 0144-8609
    Biogas - Compost - Energy - Methane - Sludge - Striped catfish

    This paper compares the quantity and quality of solid waste obtained from traditional ponds and recirculating aquaculture systems (RAS) for striped catfish and evaluates methane and compost production from these wastes. Striped catfish sludge was collected from four commercial ponds along the Mekong river and from three indoor RAS. The amount of sludge dry matter produced per kilogram of fish in ponds was 6 times higher than that in RAS. However, the concentration of nutrients in solid waste from RAS was much higher, with better compost quality and higher methane yield than that of sludge from ponds. Out of the collected 381 L biogas, the methane yield of striped catfish's solid waste in RAS systems was 201 L per kg chemical oxygen demand (COD). In ponds, the collected 267 L biogas yielded 125 L CH4 per kg COD. The higher methane production from RAS sludge concurred with higher digestibility of COD: 58% for RAS versus 38% for ponds. The quality and quantity of methane from striped catfish sludge were lower than that for other animal manures, and the resulting electricity yield was low. Considering the higher nutrient concentration in RAS-sludge, we recommend the combination RAS and composting in reusing sludge, which is presently the best option for a more sustainable and cleaner striped catfish production system.

    Effects of feed ingredients on nutrient digestibility, nitrogen/energy balance and morphology changes in the intestine of Nile tilapia (Oreochromis niloticus)
    Tran-Ngoc, Kim T. ; Haidar, Mahmoud N. ; Roem, Arjen J. ; Sendão, João ; Verreth, Johan A.J. ; Schrama, Johan W. - \ 2019
    Aquaculture Research 50 (2019)9. - ISSN 1355-557X - p. 2577 - 2590.
    digestibility - feed ingredient - intestinal morphology - nitrogen and energy balance

    The present study assessed the effect of different feed ingredients on nutrient apparent digestibility coefficients (ADC), nitrogen/energy balance and morphology changes in the intestine of Nile tilapia; using a control diet and six test diets, in which the following six ingredients were included at 30%: hydrolysed feather meal (HFM), soybean meal (SBM), rice bran (RB), rapeseed meal (RM), sunflower meal (SFM) and dried distillers grains with solubles (DDGS). The proximal, middle and distal intestine was processed for quantitative histology counting the number of goblet cells (GC), and measuring the thickness of lamina propria (LP) and submucosa (SM). The study showed that the ADC of protein in raw materials were highest in SBM (92.2%), followed by SFM (90.2%), DDGS (89.2%), RM (87.8%), HFM (86.9%) and RB (84.0%). The nutrient ADCs had no correlation with intestinal morphology changes. Only the SBM diet caused noticeable changes in intestinal morphology such as an increase the thickness of SM and LP and the number of GC. The diet composition, however, altered the protein efficiency and the maintenance energy requirement. Protein retention efficiency was the lowest in fish fed HFM and the highest in RB. The highest maintenance energy requirements were observed in HFM and SBM treatments.

    Effect of dietary protein to energy ratio, stocking density and feeding level on performance of Nile tilapia in pond aquaculture
    Kabir, K.A. ; Verdegem, M.C.J. ; Verreth, J.A.J. ; Phillips, M.J. ; Schrama, J.W. - \ 2019
    Aquaculture 511 (2019). - ISSN 0044-8486
    Benefit cost ratio (BCR) - Gross margin - Nitrogen retention - Pond aquaculture - Protein to energy (P:E) ratio

    There is growing interest to understand the dietary P:E requirements for the supplemental feed used in tilapia pond culture where natural food contributes to production. In an on-farm trial, we tested the effect of lowering dietary P:E ratio on fish performance, pond nutrient utilization and economic benefit under two stocking densities and feeding levels. Forty ponds, (average size 234 ± 112 m2), were assigned to test the effect of two diets, which differed in P:E ratio (18 vs 14 g.MJ−1), two feeding levels (14 vs 18 g.kg-0.8.d−1) and two stocking densities (2 vs 3 fish.m−2). Initial fish biomass was 45(±21) vs 67(±38) g.m−2 at 2 vs 3 fish.m−2, respectively. The experiment lasted 82 days. Decreasing P:E ratio enhanced tilapia production (P < 0.05; 459 vs 399 g.m−2). Increasing stocking density of tilapia from 2 to 3 m−2 increased biomass gain 43% (P < 0.001; 354 vs 505 g.m−2). Averaged over both diets and stocking densities, growth and feed conversion ratio increased with increasing feeding level (P < 0.001). Fish survival was unaffected by diet, stocking density and feeding level. Dissolved oxygen increased with increased stocking density with low P:E diet. The opposite happened for high P:E diet (P < 0.05). Increasing the feeding level also increased the DO concentration (P < 0.001). N retention efficiency was higher with the low P:E ratio diet (P < 0.001; 71 vs 52%) and decreased with increasing feeding level (P < 0.001). The data on N gain and N balance at the pond level suggest that the food web productivity was stimulated by reducing the dietary P:E ratio. The low P:E diet increased the gross margin by 95% (P < 0.001; 2076 vs 1067 USD.ha−1) and benefit cost ratio by 22% (P < 0.05; 1.57 vs 1.29). The P:E ratio of the low P:E diet is less than the presently advised. Lowering the P:E ratio from 18 to 14 g.MJ−1 in pond feeds for tilapia will increase the economic viability of pond aquaculture.

    Nutritious pond feed for intensive shrimp culture
    Vinasyiam, A. ; Verreth, J.A.J. ; Verdegem, M.C.J. - \ 2019
    Effect of vitamin B12 and taurine on the alleviation of nutritional anaemia in common sole (Solea solea)
    Kals, Jeroen ; Blonk, Robbert J.W. ; Mheen, Henk W. van der; Schrama, Johan W. ; Verreth, Johan A.J. - \ 2019
    Aquaculture Nutrition 25 (2019)2. - ISSN 1353-5773 - p. 456 - 465.
    anaemia - haematocrit - haemoglobin - sole (Solea solea) - taurine - vitamin B12
    Sole fed commercial pellets develop a nutritional anaemia. This study assessed the impact of dietary B12 and taurine on the haematocrit (Hct) and haemoglobin (Hb) level and mineral absorption in anaemic sole. Anaemic sole was fed one of four diets. Diets were equal regarding mineral, amino acid and macronutrient composition and formulated, according to a two by two factorial design: two B12 (0.34 vs. 1.9 mg kg dm) and two taurine levels (3.5 vs. 7.6 mg kg dm−1). The feeding level was restricted and equal for all diets. Hct and Hb levels in anaemic sole are influenced by dietary B12. A “high” level of B12 increases the Hct and Hb level. An increasing level of taurine suppresses the stimulating effect of the “high” level of B12. The applied B12 and taurine levels were unable to completely alleviate the anaemia in sole. Nevertheless, sole needs high dietary levels of B12 to alleviate anaemia. The impact of B12 and taurine on Hb and Hct was not related to a change in the absorption of iron. A “high” level of B12 positively affected the absorption of chromium and a high level of taurine negatively affected the absorption of cobalt in sole.
    Environmental conditions alter the effect of organic acid salts on digestibility and intestinal morphology in Nile tilapia (Oreochromis niloticus)
    Tran-Ngoc, Kim T. ; Huynh, Son T. ; Sendão, João ; Nguyen, Thinh H. ; Roem, Arjen J. ; Verreth, Johan A.J. ; Schrama, Johan W. - \ 2019
    Aquaculture Nutrition 25 (2019)1. - ISSN 1353-5773 - p. 134 - 144.
    digestibility - hypoxia - intestinal morphology - normoxia - organic acid - soybean meal diet

    The impact of two dietary organic acids (OAs) on nutrient digestibility and intestinal morphology was determined in Nile tilapia under conditions of dissolved oxygen in the water: normoxia and hypoxia. Four diets designated as control (0 g/kg organic acid salt), KDF (2 g/kg potassium diformate), CAB (2 g/kg calcium butyrate) and their combination (4 g/kg of a mixture of KDF and CAB, ration 1:1) were formulated with 520 g/kg of soybean meal in order to produce soybean meal enteritis-like symptoms. The four diets were tested first under normoxic conditions (6 mg/L) for a period of 5 weeks, followed by a test period under hypoxic conditions (3 mg/L). The results showed that OAs were unable to significantly improve growth and nutrient digestibility under normoxic conditions but under hypoxic conditions, there was a significant enhancement of the growth and nutrient digestibility. Fish fed OA-supplemented diets showed improvements in the intestinal morphology under the normoxic conditions, and these effects were more pronounced under the hypoxic conditions. Experimental findings suggest that OAs can improve the nutrient digestibility and intestinal morphology under hypoxic conditions. A synergistic effect by the combination of formic and butyric acid on growth, digestibility and intestinal morphology was not found.

    Effect of dietary protein to energy ratio on performance of nile tilapia and food web enhancement in semi-intensive pond aquaculture
    Kabir, K.A. ; Schrama, J.W. ; Verreth, J.A.J. ; Phillips, M.J. ; Verdegem, M.C.J. - \ 2019
    Aquaculture 499 (2019). - ISSN 0044-8486 - p. 235 - 242.
    Food web - N utilization - P:E ratio - Pond

    When fish have only access to formulated feed, the optimal dietary protein to energy ratio (P:E) for tilapia ranges between 18 and 23 g.MJ−1. In pond culture, where natural foods complement administrated feed, increasing the carbon:nitrogen (C:N) ratio stimulates the natural food productivity. This study assessed if lowering the dietary P:E ratio (and thus increasing the C:N ratio of the feed input in the pond) below the optimal P:E ratio affects fish productivity, food web dynamics and nitrogen balances in semi-intensively managed tilapia ponds. Twelve ponds, each divided into three equally-sized compartments, were assigned to test the effect of two diets, which differed in P:E ratio (19 vs. 14 g.MJ−1). Three feeding levels (no, “low” and “high”) were nested in each pond in a split plot design. Initial fish biomass was 1166 (±16) g.compartment−1 and the experiment lasted 60 days. Decreasing P:E ratio enhanced tilapia production and specific growth rate (P <.05; 1195 vs. 985 g.compartment−1 and 1.76 vs 1.55%.d−1). Body composition of tilapia was unaffected by diet and feeding level. Despite the difference in performance, final fat content was 5% of body weight and unaffected by treatments. Averaged over both diets, survival and feed conversion ratio increased with increasing feeding level (P <.001). Diet composition did not alter measured water quality, and abundance and diversity of the related parameters of the food web. The total amount of N accumulated in the pond was lower with the low P:E ratio diet (i.e., low protein diet). The data on N gain and N balance at the pond level suggest that the food web productivity was stimulated by reducing the dietary P:E ratio below the reported optimal levels in the literature. It is hypothesized that the optimal dietary P:E ratio is dependent on the culture intensity (extensive, semi-extensive or intensive pond culture).

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