Nature Institute Logo
Unintended Effects of Genetic Manipulation
A Project of The Nature Institute
Project Director:  Craig Holdrege
20 May Hill Road   ●   Ghent, NY 12075 USA   ●   Tel: (518) 672-0116   ●

Atlantic salmon fed Bt corn had altered enzyme activity in liver and intestine as well as altered proportions and numbers of different white blood cells.

Manipulated Organism: Maize (Zea mays L.).

Inserted Transgene and Intended Effect: The crylAb gene derived from the bacterium Bacillus thuringiensis (Bt), which gives the plant the ability to produce an insecticidal delta-endotoxin and confers resistance to the European cornborer, Ostrinia nubilalis. The researchers used Monsanto's commercial variety MON810, known as Bt corn or maize.

Animal Fed: Atlantic Salmon (Salmo salar L.).

Goal of This Study: Investigate whether the health of post-smolt Atlantic salmon is affected when they are fed genetically modified Bt maize (event MON810) as a starch source. The study evaluated particular substances as biomarkers for toxic and immunological stress.

In a 3-month feeding study, post-smolt Atlantic salmon were fed experimental diets differing in the type of maize used as the only starch source: genetically modified Bt corn (in this study called GM maize), an untransformed near-isogenic parental line of Bt corn (in this study called nGM maize), and commercial suprex maize from Condrico AB, Den Haag, The Netherlands. There were five experimental diets: control diet with suprex maize; two nGM maize diets with half (low) or all (high) of suprex maize replaced with nGM maize; two GM maize diets with half (low) or all (high) of suprex maize replaced with Gm maize. Low GM maize diet contained 15% (150g. per kg.) GM maize and the high GM maize diet 30%.

Results of This Study:
  • The salmon fed GM maize diets had significantly lower activity of the enzyme catalase (CAT) in the liver and higher activity of the enzyme superoxide dismutase (SOD) in the liver and distal intestine in comparison to salmon fed the control or nGM diet.
  • The salmon fed GM maize diets had significantly higher activity of CAT in the distal intestine and higher levels of the heat-shock protein 70 (HSP70, which is a protective protein reported to respond to a variety of stressors) in the liver in comparison to salmon fed the control diet.
  • There were also changes in the proportions and numbers of the different kinds of white blood cells. The salmon fed GM maize diets had a significantly higher proportion of granulocytes and a lower proportion of lymphocytes in comparison to salmon fed high nGM maize. The sum of granulocytes and monocytes was also significantly higher. These findings may indicate "some immune response resulting from the presence of GM maize in the diet. It might be that the gene modification process has resulted in the formation of new and unknown proteins that act as weak allergens" (p. 210).

Additional Comments: The authors summarize: "Thus, this study has shown that feeding Atlantic salmon GM maize resulted in small changes in CAT and SOD enzyme activities in liver and distal intestine, and HSP70 protein level in liver. These signs were indicative of a mild stress response, but were not correlated with changes in normalized gene expression of these stress proteins. Differential leukocyte counts showed altered proportions of white blood cell populations, suggestive of an immune response taking place in the blood as a response to the GM maize in the diet" (p. 211).

Source: Sagstad, A., M. Sanden, O. Haugland, A.-C. Hansen et al. (2007). "Evaluation of Stress- and Immune-Response Biomarkers in Atlantic Salmon, Salmo salar L., Fed Different Levels of Genetically Modified Maize (Bt Maize), Compared With its Near-Isogenic Parental Line and a Commercial Suprex Maize," Journal of Fish Diseases vol. 30, pp. 201-12.

Author Affiliations: National Institute of Nutrition and Seafood Research, NIFES, Bergen, Norway; Department of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, Oslo, Norway.

Funding: Not mentioned.

Product Status: Over half the corn planted in the U.S. in 2006 was Bt corn, and this corn is commonly fed to farm animals (cattle, pigs, and poultry). Since farm-raised fish are also fed corn, it is likely that they, too, are receiving Bt corn.

Copyright 2008 The Nature Institute.

This document:

--> Back to top of this document

--> Main Unintended Effects Search Page

Home | About Us | Become a Friend | Bookstore | Contact Us | Search | Calendar of Events |
Our Education Programs | Our Publications | Content Areas | Writings Ordered by Author | Resources and Links |