Something fishy down on the farm

Soaring demand for seafood has sparked huge expansion in aquaculture

but there are worries over the use of growth hormones

Clive Cookson / Financial Times 2dec00

Aquaculture is the fastest growing of the world's main agricultural sectors. More than 30m tonnes of farmed fish and seafood will be produced this year, with output growing by 10 per cent annually. With catches of many wild species falling because of over-exploitation - and demand for fish and crustaceans rising fast - aquaculture is the only way to fill the gap.

Although aquaculture has a long history in Asia - Chinese farmers have been raising carp in ponds and rice paddies for 3,000 years - it has only been carried out on an industrial scale in Europe and North America for a couple of decades. It is therefore primitive, in the technological sense, compared with land-based farming.

Whereas cattle, sheep, pigs and chickens have been bred for thousands of years for agricultural use, farmed fish are similar to their wild counterparts. Farmers have hundreds of years experience in keeping domesticated animals healthy in confined conditions - veterinary medicine is one of the most sophisticated sciences - while relatively little is known about the diseases and stress suffered by captive fish or about the best environment in which to rear them.

Several countries are therefore making a big effort to put aquaculture on to a better technical footing, as the recent Pacific Rim Biotechnology Conference heard in Vancouver. For example, the Canadian government will spend CDollars 75m (Pounds 35m) over the next five years on research and development to support the country's aquaculture industry, where sales are projected to rise from CDollars 500m in 1998 to CDollars 1.5bn in 2005.

Many people associate fish biotechnology with genetic modification, particularly for fast growth. And there have indeed been spectacular achievements in the laboratory, though no GM fish have yet been commercialised.

The champion growth enhancement reported to the Vancouver conference is in mud loach -a freshwater fish favoured by Koreans. Dong Soo Kim of Pukyong University has made a GM strain of mud loach that grows 30 times faster than the normal fish.

The loach is a small fish, normally weighing about 10g, while Kim's GM version can grow up to 500g. He says the GM monsters, which contain extra growth hormone genes, "taste just the same as the normal fish", but he does not expect them to be approved for the consumer market for 10 years.

Of more immediate relevance to Europe and North America are GM salmon, which grow about five times faster than unmodified fish. The US Food and Drug Administration is considering an application by A/F Protein, a Canadian-US company, to commercialise this process. No one knows how long the FDA review will take or how many fish farms would risk a consumer backlash against "Frankenfish" by adopting GM salmon, if the application is granted.

Although GM fish convert food into protein more efficiently than their normal counterparts, they are bound to face strong opposition. There will be health concerns about eating fish with added growth hormones and associated promoter genes but the environmental concerns are stronger.

Even though GM fish can be made sterile by manipulating their chromosomes, opponents will claim that the sterilisation process is not 100 per cent efficient. If transgenic (GM) salmon escape and interbreed with wild stock, the ecological consequences could be serious.

Indeed, one of the concerns about non-GM salmon farming is that escaping fish are undermining the genetic purity of the individual river-specific strains that have evolved over many centuries - possibly weakening their capacity to survive in the wild. Like the human being, the Atlantic salmon is a single species that has no subspecies but significant racial variation.

For many in aquaculture research, genetic manipulation for growth is a red herring that threatens to antagonise public opinion without addressing the more important issues of fish health and sustainable development.

Scott LaPatra, R&D director of Clear Springs Foods in Idaho, the world's largest producer of trout, says: "We are not allowed to work on transgenics; the issue is too sensitive. Our number one issue is environmental control of effluents."

Clear Springs, which produces 20m pounds of rainbow trout a year in farms on the scenic Snake River Canyon, has a traditional selective breeding policy, selecting for fast-growing fish, though LaPatra admits it is not clear to what extent this has actually improved the stock. "We still do not know the optimal way to grow these fish," he says.

One research project, involving Clear Springs and public laboratories, is to develop a DNA vaccine to protect trout and salmon against the virus that causes infectious haematopoietic necrosis, a serious disease of farmed fish. Although it involves injecting a viral gene into fish, it does not produce transgenic (GM) fish that pass the genes on to future generations. Even so, consumers will have to be reassured that the practice is safe.

Yonathan Zohar, director of the University of Maryland's Centre of Marine Biotechnology, says fish vaccination lags far behind its veterinary counterpart. One bottleneck is the inefficiency of injecting slippery young fish. He predicts that DNA vaccines will be developed for diluting in water and administering to hundreds of fish simultaneously in tanks.

At the same time, scientists are investigating the molecular interplay of pathogens (germs), stress and the fish's immune system, which determine the success of aquaculture. If, for example, they can find genetic markers for stress hormones in fish, it might be possible to short-cut the conventional breeding route to produce salmon better suited to a life in captivity.

Fish have a temperature-dependent immune system that is different from that of warm-blooded mammals. Laura Brown, head of cell and molecular biology at Canada's Institute for Marine Biosciences in Nova Scotia, says cold-water fish are vulnerable to two dozen known water-borne pathogens. "Fish are more at the mercy of their environment than land animals," she says. "It really has to be pristine."