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Unintended Effects of Genetic Manipulation
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Tilapia fish engineered for transgenic expression of growth hormone had deformed heads and backs, atrophied gonads, and lower mineral content.

Manipulated Organism: Tilapia (Oreochromis niloticus).

Inserted Transgenes: Tilapia growth hormone gene, with expression controlled by the beta-actin promoter from medaka fish.

Goal of This Study: Compare the growth of tilapia expressing the growth hormone transgene with their non-GM siblings.

Intended Effect: At 87 days post hatching, the average body weight of the GM fish was nearly 3 times that of the non-GM fish. By 147 days, the GM fish had reached market weight (165 g), while the non-GM fish required an additional 90 days to reach that size.

Results of This Study: Numerous morphological and compositional differences were observed when the fish were harvested (at the same weight but months apart), including:
  • The GM fish had larger heads and wider bodies. Some had deformed, even fractured, backs and heads.

  • The viscera of the GM fish were 8% of their total body weight compared with 6% for the non-GM fish (p < 0.01).

  • The gonads of the GM fish were strongly atrophied, comprising only 0.05% of the total body weight compared with 1.0% for the non-GM fish.

  • The GM fish had a higher moisture content (77% versus 70%) and contained significantly less calcium (Ca) and phosphorus (P). On a dry weight basis, the GM fish had only 72% and 86% of the Ca and P, respectively, of the non-GM fish at market weight. The authors interpret this fact as indicating incomplete bone mineralization, which is consistent with the observation of bone fractures in the GM fish.

Source: Lu, J., J. Li, Y. Furuya, G. Yoshizaki et al. (2009). "Efficient Productivity and Lowered Nitrogen and Phosphorus Discharge Load from GH-Transgenic Tilapia (Oreochromis niloticus) under Visual Satiation Feeding," Aquaculture vol. 293, pp. 241-7.

Author Affiliations: Tokyo University of Marine Science and Technology, Japan.

Funding: Japanese Ministry of Education, Science, Sport and Culture.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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