You are incorrect in assuming that US federal-agency decisions on genetically modified (GM) organisms are always based on sound science and that Congress might be undermining such decisions (Nature 475, 5; 2011).
In the case of GM salmon, the Advisory Committee of the US Food and Drug Administration (FDA) scolded the FDA and the salmon-production company AquaBounty of Waltham, Massachusetts, for overlooking important scientific issues during the approval process. Criticisms included inadequate sample sizes, incomplete data, questionable culling practices, troubling physical abnormalities, a failed test for allergenicity, and poor environmental and scientific assessments. So far, the agency has not corrected any of these oversights.
Furthermore, the FDA has never promulgated mandatory regulations or amended existing ones to cover GM animals. Instead, it announced in its non-binding 2009 Guidance for Industry (see http://go.nature.com/nvcvnx) that it would approve such animals under its existing 'new animal' drug law. As a result, the FDA — which has insufficient scientific expertise in assessing fisheries and environmental risk — is giving itself the task of reviewing and assessing GM fish. This is hardly a prescription for sound science.
Rather than blaming Congress, we should be glad that it has stepped in to address this serious economic, human-health and environmental issue.