Genetically modified plants as fish feed ingredients. Roundup Ready® soy, MON810 maize, Atlantic salmon, zebrafish
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Commonly used plant ingredients in salmon feed such as soybeans and maize are increasingly grown as genetically modified (GM) varieties. The question arises whether these are equally nutritious and safe for the fish as conventional varieties. The target species of this thesis is Atlantic salmon (Salmo salar), while zebrafish (Danio rerio) is used as a potential model. Extensive evaluations of performance, health, organ function and stress response were carried out in a 7-month salmon feeding trial with GM soy (25%). A smaller study was conducted on zebrafish evaluating both GM soy and GM maize as feed ingredients, including tracing of dietary DNA in fish tissues. Feeding salmon GM soy did not affect growth, body composition, haematology or weights of liver, spleen, head-kidney and proximal intestine, compared to non-GM soy. Distal intestine was larger in the GM group at one sampling point, but not at the end of the trial. Mid intestine was consistently smaller in the GM group. Typical soybean meal (SBM) -induced alterations in the distal intestine were seen in both groups. However, GM fed fish had shorter mucosal fold height at one sampling point, and more mucosal fold fusion overall in the trial, which could indicate slightly more pronounced SBM-induced changes. In liver, glycogen deposits were lower in salmon fed GM soy. Apart from this, no morphological differences were detected in any organs. Of parameters related to health, there were no differences in haematology, proportion of leukocytes types, lysozyme concentrations in spleen and head-kidney, or concentrations of plasma enzymes. Plasma triacylglycerol (TAG) was higher in the GM group overall in the trial, while no diet effects were seen on plasma glucose and protein. Fish in both diet groups responded similarly to seawater transfer; they adapted well and rapidly regulated chloride ion content in plasma back to basal levels. Similarly, there were no differences in stress response between the two diet groups. Proteomic comparisons of livers from fish in the two diet groups exhibited small fold differences, and differentially expressed proteins all had a high false discovery rate. The diet groups were not distinguishable by principal component analysis, suggesting that other sources of variation such as individual or technical variation were more prominent than the difference between fish fed GM and non-GM soy. Concluding from the salmon trial, minor diet effects were seen. In parameters where reference values are found in the literature, both diet groups were within the normal range. The present results did not confirm observations from previous trials of increased spleen size and lysozyme levels. The response in plasma TAG was opposite of what has been observed previously, suggesting that this response was not caused by the genetic modification, but by other factors like small variations in antinutrients. No indications of adverse health effects and no difference in performance during 7 months, lead to the conclusion that GM soy appears to be an equally good feed ingredient as non-GM soy at a 25% inclusion level, which is higher than what is used commercially at present. The use of zebrafish as a model greatly reduces the cost and duration of trials evaluating GM plants as feed ingredients. Soy and maize of GM and non-GM varieties were used in a 2x2 factorial design, in a 20-day feeding trial. Fish fed GM maize had better growth, lower mRNA level of superoxide dismutase-1 (SOD-1) in liver and a tendency towards lower level of heat shock protein (HSP)70 compared to fish fed non-GM maize. These results are very different to a previous salmon study using the exact same batch of maize, which could limit the usefulness of zebrafish as a model. With GM soy, there was no effect on growth, but there were significant interaction effects between soy variety (whether GM or not) and sex on total RNA yield from liver and SOD-1 level in liver. These might have been caused by isoflavones. Results from the zebrafish trial were inconclusive, both on use of GM maize in feeds and zebrafish as a model. Tracing of dietary DNA, however, was successfully accomplished with results corresponding well with work done in other species.
Paper 1: Aquaculture 294(1-2), Sissener, N. H.; Sanden, M.; Bakke, A. M.; Krogdahl, Å.; Hemre, G. I., A long term trial with Atlantic salmon (Salmo salar L.) fed genetically modified soy; focusing general health and performance before, during and after the parr-smolt transformation, pp. 108-117. Copyright 2009 Elsevier B.V. Full text is not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1016/j.aquaculture.2009.05.002Paper 2: Aquaculture 298(1-2), Sissener, N. H.; Bakke, A. M.; Gu, J.; Penn, M. H.; Eie, E.; Krogdahl, Å.; Sanden, M.; Hemre, G. I., An assessment of organ and intestinal histomorphology and cellular stress response in Atlantic salmon (Salmo salar L.) fed genetically modified Roundup Ready® soy, pp. 101-110. Copyright 2009 Elsevier B.V. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1016/j.aquaculture.2009.10.011Paper 3: Marine Biotechnology 12(3), Sissener, N. H.; Martin, S. A. M.; Cash, P.; Hevrøy, E. M.; Sanden, M.; Hemre, G. I., Proteomic profiling of liver from Atlantic salmon (Salmo salar) fed genetically modified soy compared to the near-isogenic non-GM line, pp. 273-281. Copyright 2009 Springer Science + Business Media. Full text not available in BORA due to publisher restrictions. The published article is available at: http://dx.doi.org/10.1007/s10126-009-9214-1Paper 4: British Journal of Nutrition 2010 103(1), Sissener, N. H.; Johannessen, L. E.; Hevrøy, E. M.; Wiik-Nielsen, C. R.; Berdal, K. G.; Nordgreen, A.; Hemre, G. I., Zebrafish (Danio rerio) as a model for investigating the safety of genetically modified feed ingredients (soy and maize); performance, stress response and uptake of dietary DNA sequences, pp. 3-15. Copyright 2009 The Authors. Published by Cambridge University Press. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1017/S0007114509991401