An assessment of organ and intestinal histomorphology and cellular stress response in Atlantic salmon (Salmo salar L.) fed genetically modified Roundup Ready® soy

This study was conducted to investigate potential differences between genetically modified (GM) Roundup Ready® soy and its near-isogenic maternal line as feed ingredients for Atlantic salmon, with focus on intestinal changes commonly caused by soybean meal, histomorphology of other organs and stress response. A 7-month feeding trial was conducted with an inclusion level of 25% GM soy in the diet. Samples for histology were collected after 4 months, after 6 months, when a cross-over of the diet groups was conducted, and at the end of the trial of the crossed-over groups. Histomorphology of spleen, head kidney and mid intestine exhibited no differences between the diet groups, while glycogen deposits in liver were decreased in the GM fed fish at the final sampling. Common soybean meal-induced changes of the distal intestine in Atlantic salmon were observed in both diet groups at all sampling points, within levels expected at the current inclusion level of soy in the diets. However, mucosal fold height in the distal intestine was lower in the GM fed group at one of the three sampling points, and mucosal fold fusion was more pronounced in this group overall in the trial. A stress test conducted at the end of the trial gave responses in haematological parameters, plasma nutrients and mRNA transcription of heat shock protein (HSP) 27 in both liver and distal intestine, but responses were similar between the two diet groups, indicating similar ability to handle stress. The cross-over design, implemented to look at reversibility of potential GM-effects, proved to be inadequate as the crossing of diet groups in itself caused responses that would obscure possible minor diet effects. In conclusion, minor differences were observed between the diet groups; however, GM soy did not appear to cause any adverse effects on organ morphology or stress response compared to non-GM soy.