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- Brijs, Jeroen, et al.
(author)
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The final countdown: Continuous physiological welfare evaluation of farmed fish during common aquaculture practices before and during harvest
- 2018
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In: Aquaculture. - : Elsevier BV. - 0044-8486 .- 1873-5622. ; 495, s. 903-911
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Journal article (peer-reviewed)abstract
- Welfare of farmed fish has become of increasing concern for consumers, producers, interest groups and authorities. To improve fish welfare, it is necessary to find indicators that can identify stressful situations early enough so that an intervention can take place before detrimental effects occur. By using heart rate bio-loggers in freely swimming rainbow trout (Oncorhynchus mykiss), combined with plasma cortisol levels and a range of haematological and blood chemistry parameters, we assessed the severity of stress responses induced by a range of common aquaculture practices before and during harvest. Following surgery, transportation and reintroduction with conspecifics in the sea cage, it took similar to 4 days for heart rate to stabilize and for a clear circadian rhythm in heart rate to emerge (i.e. average circadian fluctuation in heart rate of similar to 25 to 27 beats min(-1)). The presence or absence of this circadian rhythm in heart rate could inform researchers in the aquaculture industry whether or not specific farming routines induce unnecessary and prolonged stress. The elevations in heart rate caused by common farming practises such as crowding and transportation (e.g. heart rate increased by similar to 8 and 9 beats min-1 above what would normally be expected for that time of day, respectively) corresponded well with increases in plasma cortisol levels. Stressful farming practises or events (indicated by elevated plasma cortisol levels) such as air exposure during brailing and aquatic hypoxia triggered a hypoxic bradycardia until fish were released back into oxygenated water whereupon heart rate significantly increased to repay the accumulated oxygen debt. Repeated stress induced by multiple farming practises (i.e. combined stressors of crowding, brailing and transportation) clearly had a cumulative and long-lasting effect as heart rate peaked at similar to 25 beats min(-1) above what would normally be expected for that time of day. Heart rate also remained significantly elevated by similar to 9 beats min(-1) the following morning, suggesting that if rainbow trout need to be subjected to multiple stressors during consequtive days, it is recommended that sufficient time for recovery is provided between stressors. This study demonstrates that heart rate monitoring can be useful to assess stress levels of freely swimming fish in sea cages. Moreover, the use of implantable bio-loggers opens up a broad range of possible applications that will allow researchers to investigate the effects of environmental and/or anthropogenic stressors on the welfare of fish under conditions more realistic to the aquaculture industry.
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- Huyben, David, et al.
(author)
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Dietary live yeast and increased water temperature influence the gut microbiota of rainbow trout
- 2018
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In: Journal of Applied Microbiology. - : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 124, s. 1377-1392
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Journal article (peer-reviewed)abstract
- Aims: The objective was to determine the effects of dietary substitution of fishmeal (FM) with live yeast and increasing water temperature on the diversity and composition of gut microbiota in rainbow trout.Methods and Results: Fish were fed either FM or yeast (Saccharomyces cerevisiae) and reared in water temperatures of either 11 degrees C (cold) or 18 degrees C (warm) for 6 weeks. Luminal content and mucosa were collected from the distal gut and the load, diversity and species abundance of yeast and bacteria were analysed using agar plating, MALDI-TOF and rRNA gene amplicon sequencing. Yeast in the gut of fish fed FM were represented by S. cerevisiae, Rhodotorula spp. and Debaryomyces hansenii, while fish fed yeast contained 4-5 log higher CFU per g of yeast that were entirely represented by S. cerevisiae. For gut bacteria, sequencing of 16S rRNA gene amplicons using Illumina MiSeq showed lower bacterial diversity and abundance of lactic acid bacteria, especially Lactobacillus, in fish reared in warm rather than cold water. Fish fed yeast had similar bacterial diversity and lower abundance of Leuconostocaceae and Photobacterium compared with fish fed FM.Conclusions: Feeding live yeast mainly increased yeast load in the gut, while increased water temperature significantly altered the gut microbiota of rainbow trout in terms of bacterial diversity and abundance.Significance and Impact of the Study: Live yeast can replace 40% of FM without disrupting bacteria communities in the gut of rainbow trout, while increased water temperature due to seasonal fluctuations and/or climate change may result in a gut dysbiosis that may jeopardize the health of farmed fish.
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- Huyben, David, et al.
(author)
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Effects of dietary inclusion of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus on gut microbiota of rainbow trout
- 2017
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In: Aquaculture. - : Elsevier BV. - 0044-8486 .- 1873-5622. ; 473, s. 528-537
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Journal article (peer-reviewed)abstract
- Rainbow trout (Oncorhynchus mykiss) were fed for 10 weeks on a diet containing either 30% fish meal (FM) or with 20, 40 and 60% replacement of fish meal protein with Saccharomyces cerevisiae (SC) or a mixture of Wickerhamomyces anomalus and S. cerevisiae(WA). Luminal contents and mucosal tissue from the distal intestine were collected and analysed for yeast and bacterial loads by agar plating. Diversity and abundance were determined by sequencing of amplicons generated from the 26S rRNA (yeast) and 16S rRNA (bacteria) genes. In addition, the diets were analysed before and after feed extrusion to determine the viability and composition of the yeasts ingested by the fish. After extrusion, 9-10 log cells g(-1) of yeast were still intact in the SC and WA diets, but culturable yeast showed log-reductions of 5-7 CFU g(-1). For yeasts isolated from the gut contents, 81-96% of colonies consisted of Debaryomyces hansenii, with few or no colonies of S. cerevisiae or W. anomalus despite their high inclusion rate in the diets. Characterisation of gut bacteria using Illumina MiSeq showed that 70 and 19% of sequences were classified to the phyla Firmicutes and Proteobacteria, specifically sequences identified as Leuconostocaceae, Lactobacillaceae and Photobacterium. Compared with the FM diet, the WA40 diet reduced bacterial diversity, whereas the WA60 diet increased the abundance of the pathogenic yeast Candida albicans and reduced lactic acid bacteria in the gut. Overall, 40 and 60% replacement of fish meal protein with a mixture of W. anomalus and S. cerevisiae significantly altered the gut microbiota of rainbow trout, while 20% replacement and diets with only S. cerevisiae had little or no effect. (C) 2017 Elsevier B.V. All rights reserved.
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| 7. |
- Huyben, David, et al.
(author)
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Effects of dietary yeast inclusion and acute stress on post-prandial whole blood profiles of dorsal aorta-cannulated rainbow trout
- 2017
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In: Fish Physiology and Biochemistry. - : Springer Science and Business Media LLC. - 0920-1742 .- 1573-5168. ; 43, s. 421-434
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Journal article (peer-reviewed)abstract
- Yeast is a potential alternative to fish meal in diets for farmed fish, yet replacing more than 50 % of fish meal results in reduced fish growth. In a 4-week experiment, 15 rainbow trout (Oncorhynchus mykiss) were cannulated and fed three diets each week: 30 % fish meal as a control (FM); 60 % replacement of fish meal protein, on a digestible basis, with Saccharomyces cerevisiae (SC); and 60 % replacement with Wickerhamomyces anomalus and S. cerevisiae mix (WA). Blood was collected at 0, 3, 6, 12 and 24 h after feeding. In the final week, fish were exposed to a 1-min netting stressor to evaluate possible diet-stress interactions. Significant increases in pH, TCO2, HCO3 and base excess were found after fish were fed the SC and WA diets compared with FM, which elevated blood alkaline tides. Yeast ingredients had lower buffering capacity and ash content than fish meal, which explained the increase in alkaline tides. In addition, fish fed the WA diet had significantly reduced erythrocyte area and fish fed SC and WA diets had increased mean corpuscular haemoglobin levels, indicating haemolytic anaemia. Higher levels of nucleic acid in yeast-based diets and potentially higher production of reactive oxygen species were suspected of damaging haemoglobin, which require replacement by smaller immature erythrocytes. Acute stress caused the expected rise in cortisol and glucose levels, but no interaction with diet was found. These results show that replacing 60 % of fish meal protein with yeasts can induce haemolytic anaemia in rainbow trout, which may limit yeast inclusion in diets for farmed fish.
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| 8. |
- Huyben, David, et al.
(author)
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Effects of dietary yeast inclusion and acute stress on postprandial plasma free amino acid profiles of dorsal aorta-cannulated rainbow trout
- 2018
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In: Aquaculture Nutrition. - : Hindawi Limited. - 1353-5773 .- 1365-2095. ; 24, s. 236-246
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Journal article (peer-reviewed)abstract
- In a 4-week experiment, 15 cannulated rainbow trout were fed three diets based on fish meal (FM), Saccharomyces cerevisiae yeast (SC) and Wickerhamomyces anomalus and S.cerevisiae yeast mix (WA). Fish were fed daily, and blood samples were collected on day 7 of each week at 0, 3, 6, 12 and 24hr after feeding. In the final week, fish were exposed to a 1-min netting stressor. All essential and non-essential plasma amino acid levels except methionine were similar between fish fed diets FM, SC and WA. Plasma methionine and sarcosine were significantly higher in fish fed diets SC and WA, possibly due to the crystalline methionine level, form or feeding regime. Hydroxy-proline and 3-methyl-histidine were higher in fish fed diet FM, which can be explained by the higher levels present in fish meal compared with yeast. In stressed fish, there were no dietary effects on plasma amino acid levels, but significant increases in taurine and cystathionine were found in stressed compared with unstressed fish. These results demonstrate that yeast-based diets produce similar plasma amino acid profiles to fish meal and suggest that yeast may be a suitable fish meal replacement in diets for rainbow trout.
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| 9. |
- Huyben, David
(author)
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Effects of feeding yeasts on blood physiology and gut microbiota of rainbow trout
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Yeast represents a sustainable protein alternative to fishmeal in diets for farmed fish, although more than 40% replacement has been shown to reduce fish growth and welfare. This thesis investigated the effects of feeding high inclusions of inactivated and live yeasts to fish in order to replace fishmeal without negative health consequences. The specific focus was on red blood cell characteristics, plasma amino acid uptake, gut microbial communities and stress/immune responses of rainbow trout (Oncorhynchus mykiss). Post-prandial blood samples were collected from dorsal aorta-cannulated rainbow trout fed diets in which 60% fishmeal protein was replaced with two yeast species, Saccharomyces cerevisiae and Wickerhamomyces anomalus, inactivated by heat extrusion. Blood analysis showed that feeding both yeasts resulted in higher blood pH and haemoglobin levels, which were associated with lower buffering capacity of yeast and possible haemolytic anaemia from metabolism of high levels of nucleic acid. Plasma analysis revealed that amino acid uptake was similar in fish fed both yeasts and fishmeal, except for higher methionine in fish fed yeasts attributed to higher supplementation. In a later study, fish were fed live S. cerevisiae and reared at 11 and 18°C. No adverse effects on blood physiology were found, although most cells survived digestion and were not metabolised. These results indicate that reduced growth in fish fed yeast may not be due to lower amino acid content, but rather to metabolism of high levels of nucleic acid leading to impaired red blood cell function. In separate studies, fish were fed inactivated yeasts that replaced 20, 40 and 60% of fishmeal protein and fish kept at 11 and 18°C were fed 40% replacement with live yeast. High-throughput sequencing of the distal gut revealed that inactivated W. anomalus affected bacterial diversity and abundance, while both inactivated and live S. cerevisiae had minor effects. Increased temperature reduced the abundance of lactic acid bacteria and reduced bacterial diversity. In both studies, Debaryomyces hansenii, S. cerevisiae and Rhodotorula spp. were naturally present in the fish gut and feeding live yeast, but not inactivated, increased the gut yeast load. Fish at 18°C had higher plasma cortisol levels and suppressed expression of inflammatory cytokines, which were further suppressed when fed live yeast. This suggests that increased temperature subjected fish to chronic stress and that feeding live yeast may impair the innate immune response. In conclusion, this thesis suggest that impaired red blood cell and immune function are key factors reducing growth and welfare of rainbow trout fed yeast and managing these factors may enable sustainable replacement of fishmeal.
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| 10. |
- Huyben, David, et al.
(author)
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Effects of feeding yeasts, Saccharomyces cerevisiae and Wickerhamomyces anomalus, on gut microbiota of rainbow trout
- 2016
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Conference paper (other academic/artistic)abstract
- Introduction Single cell proteins, such as yeasts, are an ideal feed alternative to plant and fish meals as they do not compete as food for humans. Previous studies have fed live yeast, such asSaccharomyces cerevisiae, in cold pelleted diets to farmed fish in order to increase beneficial microbiota in the gut (Gatesoupe, 2007). However, commercial salmonid diets are typically extruded at high temperatures, which can inactivate yeasts and reduce their effects on gut microbiota. In addition, previous studies have used culture-based methods to determine gut microbiota, while the development of next generation sequencing has improved identification of unculturable microbiota. The objective of this study was to determine the effect of feeding yeasts,S. cerevisiae and Wickerhamomyces anomalus, on microbiota in the distal intestine of rainbow trout (Oncorhynchus mykiss). Materials and methods A diet of fish meal (FM) was used as a control against yeast diets that replaced 20, 40 and 60% of fish meal (digestible protein basis) with either S. cerevisiae(SC) orW.anomalus/S. cerevisiaemix (WA; Jästbolaget AB, Sweden). Diets were extruded at 120-130oC and later fed to triplicate tanks of 35 rainbow trout for 10 weeks. Afterwards, content and mucosa from the distal intestine of 3 fish per tank were collected. Ingredients, diets and gut samples were plated on yeast-peptone-D-glucose, then 26S rDNA were PCR-amplified and sequenced to determine live yeast counts and taxa. Diets and yeast ingredients were further examined microscopically to determine cell counts of yeast. For gut bacteria, 16S rDNA were PCR-amplified, barcoded and next generation sequenced using Illumina platform (SciLifeLab AB, Sweden). Significant differences (p<0.05) between diets were determined using ANOVA and ANOSIM methods. Results The yeast ingredients,S. cerevisiaeor W. anomalus/S. cerevisiae mix, contained between 9-10 log cfu g-1and SC and WA diets contained 7-8 log cfu g-1before extrusion. After extrusion, all diets had over 4-log reduction in cfu g-1(cultured yeast), however 7-8 log cells g-1of yeast were still viable. Diets of SC and WA contained between 96-100%S. cerevisiaeand 0-20%W. anomalus.After 10 weeks of feeding, the distal intestine contained between 84-96 Þbaryomyces hanseniiwith few colonies of S. cerevisiae and noW. anomalus. For bacteria, the distal intestine contained between 37-62 % ofLeuconostocaceae,Lactobacillaceae and Photobacteriumand significant differences in taxa abundance and similarity were found between fish fed SC60, WA40 and WA60 compared with the FM diet (Fig. 1). Discussion and conclusion This study is the first to analyse intestinal microbiota of rainbow trout fed yeast diets using next generation sequencing. In addition, few studies have investigated the viability and log reduction of yeast after feed extrusion. The low level of culturable yeast compared with the high level of intact yeast cells found after diet extrusion suggested that high temperature from extrusion inactivated yeasts, but did not disrupt the cells. Inactivated, non-disrupted yeast is not ideal because the yeast cannot cultivate the intestine or release nutrients for metabolic uptake. The lack of S. cerevisiaeandW. anomalusin the distal intestine despite the high level of yeast ingestion, suggests that large amounts of yeast were metabolised. However, higher levels of unculturable yeast cells may have been present in the intestinal content and mucosa. For gut bacteria, most were Lactic Acid Bacteria (Lactobacillales order), which includesCarnobacteriaceae, Leuconstocaceae, Leuconstocaceaeand Streptococcaceae families. In comparison, Ingerslev et al. (2014) found similar levels ofStreptococcus, Leuconostoc,Enterobacteriaceae and Lactobacillusin rainbow trout fed fish and plant-based diets.Significant differences in bacteria abundance for fish fed SC60, WA40 and WA60 diets indicated thatW. anomalushad a higher effect thanS. cerevisiaeand that more than 20% replacement of fish meal with yeast affected gut microbiota in rainbow trout. References Gatesoupe F.J. 2007. Live yeasts in the gut: Natural occurrence, dietary introduction, and their effects on fish health and development. Aquaculture 267: 20-30. Ingerslev H.C., L. von Gersdorff Jørgensen, M. Lenz Strube, N. Larsen, I. Dalsgaard, M. Boye, and L. Madsen. 2014. The development of the gut microbiota in rainbow trout (Oncorhynchus mykiss) is affected by first feeding and diet type. Aquaculture 424-425: 24-34.
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