A young pink salmon infected with sea lice. (Courtesy of Alexandra Morton/Science)

Fish farming has had a bad rap, but will continue to grow quickly, may be the only way to meet rising demand for seafood and isn't necessarily an environmental problem, a U.S. scientist says.

The catch from traditional fishing fisheries has remained about constant for 20 years, but production from aquaculture has risen 8.8 per cent per year since 1985, James S. Diana of the University of Michigan at Ann Arbor said in an assessment published Friday.

Aquaculture accounts for about a third of the total weight of fish and related products, and is expected to rise, whereas traditional fishing weights may fall, he said in the January issue of BioScience.

Diana acknowledges the well-publicized problems with fish farming:

• The escape of farmed species that then become invasive or infect wild species with diseases.
• The pollution of local waters by fish-farm effluent.
• Changes in land use, especially associated with shrimp farms.

For example, parasitic sea lice from salmon farms may almost eradicate the wild population of B.C. pink salmon in eight years, researchers reported in 2007.

But with good practices, aquaculture may be no more harmful than other agricultural techniques, Diana said.

Done carefully, aquaculture can reduce pressure on overexploited wild stocks, enhance depleted stocks and boost species diversity, he said.

Fish farming is also important to developing countries, where it can create employment. Seafood exports generate more money for developing countries than meat, coffee, tea, bananas and rice combined, he said.

He recommended more life-cycle analyses to compare aquaculture with other food-production systems.