Aquaculture -- the farming of fish, shellfish and aquatic plants -- is a burgeoning industry that should take greater care not to import and spread invasive species, say ecologists at the University of California, Davis, and Stanford University.

In the Nov. 23 issue of the journal Science, the researchers write that exotic species of seaweed, fish and mollusks escape frequently from aquaculture facilities, creating "biological pollution" with unpredictable and irreversible effects on native ecosystems.

For example, along the Pacific coast of North America, the farming of Atlantic salmon threatens native fish. In the Pacific Northwest, more than a half-million Atlantic salmon escaped from farm pens between 1987 and 1997, and they and their descendants have been found in 77 British Columbia rivers.

Aquaculture now supplies one-third of the seafood consumed worldwide; U.S. facilities alone are expected to increase their output five-fold by 2025, says the report. The authors are Susan Williams, director of the UC Davis Bodega Marine Laboratory, professor of environmental science and policy and an authority on shallow-water marine systems; Donald Strong, a UC Davis professor of evolution and ecology and an authority on invasive species; and Rosamond Naylor, a senior fellow at the Center for Environmental Science and Policy at Stanford University.

The authors call for U.S. policy-makers to enact clear, effective regulations to replace the current "regulatory quagmire" that now governs the aquaculture industry and government conservation agencies. They point to two models: New Zealand's Hazardous Substances and New Organisms Act of 1996 and the global Convention on Biological Diversity. In particular, those models suggest raising native species in aquaculture, rather than introduced species.