Aquaculture: the blue revolution.

While the number of wild fish plummets, those raised in captivity are getting more numerous. The process of rearing fish in controlled conditions is called aquaculture or fish farming.

Starting from an insignificant total production, inland and marine aquaculture production grew by about five percent per year between 1950 and 1969 and by about eight percent per year during the 1970s and 1980s, and it has increased further to 10% a year since 1990.

What could be simpler? Build a tank or fence off a corner of shoreline, toss in some tiddlers, feed them, and then scoop them out when they are fully grown.

Unfortunately, aquaculture is not without its controversies.

In China, where millions of people are being fed by fish farms, the farms raise mostly herbivorous fish (carp and milkfish) and invertebrates (clams and oysters). It is important to note that these fish and shellfish do not require fishmeal in their diet. In contrast, most large-scale shrimp farms and salmon farms require large amounts of fishmeal because the animals being raised are carnivorous. For every kilo of shrimp and salmon produced in this manner, a bit more than two kilos of fishmeal are required as input. And, of course, the source of the fishmeal is the endangered wild species.

Industrial production of shrimp is carried out mostly in developing countries in tropical regions. In many of these nations, mangrove forests and wetlands have been destroyed to make way for the fish farms. Mangrove forests are vital as breeding grounds for many species of commercially important fish. The ponds in which the shrimp are kept are often stocked very densely creating a perfect environment for diseases to spread quickly. An epidemic virtually wiped out the aquaculture shrimp industry in the late 1980s. It went from producing 90,000 tonnes to almost nothing in four years. When a catastrophe such as this happens, the farms are often abandoned and a new section of mangrove forest is cut down to open up a new operation.

Effluent from the shrimp farms is also a problem. One aquaculture expert visited a shrimp pond that had been drained for cleaning. It produced "the nastiest smell I've ever smelled." Because environmental controls in developing countries are few or non-existent, these problems go unchecked.

Critics say that local communities do not generally benefit from shrimp aquaculture. The shrimp are exported, the workers are usually hired from outside the community, and the income made by urban investors does not "trickle down" to local people.

These days, if you order salmon in a restaurant or buy it at the supermarket chances are it was farmed. Salmon farms in countries such as Canada, Norway, Chile, and the United States now produce most of the salmon sold on the world market. As with shrimp, salmon eat huge amounts of fishmeal, but there are other issues that concern many people.

Farmed salmon are usually raised in floating netcages anchored close to shore where crowded conditions help the spread of disease and parasites. Many salmon farmers use antibiotics and chemicals to overcome these problems. Others employ hormones to make the fish to reach market size faster.

Then, there's the escape problem.

Salmon farms usually raise Atlantic salmon because it is a faster growing species than Pacific salmon. In Norway and Scotland escaped salmon have entered local watercourses. In many of Norway's rivers, wild populations of Atlantic salmon have been completely displaced by farmed salmon. Marine biologists in British Columbia and Washington state are concerned about the same problem. Increasing numbers of escaped Atlantic salmon are being found spawning in local rivers where native populations of endangered Pacific salmon are struggling to survive.

Now, a new threat may be emerging in the form of genetically modified fish. In March 2001, Jo Dufay of Greenpeace wrote that: "Foreign genetic material has been inserted into Atlantic, coho and chinook salmon, rainbow trout, and tilapia to increase their size, growth rates, and resistance to cold temperatures. These traits may appear economically attractive in the short term, but could constitute a grave danger both to the environment and to wild fish populations." Jo Dufay and some prominent scientists lose sleep because of several potential risks:

* Genetically modified fish are big eaters and could out-compete native species for available food supplies;

* Most GM fish, but not all, are sterile (this is deliberate to reduce risk from escapes). However, native species don't know the transgenic fish are sterile and will happily mate with them. This could lead to large-scale reproductive failures;

* Finally, there is something called the "Trojan gene." If an abnormality in a fertile GM fish gets into the wild population it could wreak havoc. Jo Dufay writes that "Computer modelling done by Purdue University in Indiana estimates that 60 fertile GM fish introduced into a natural population of 60,000 could decimate the stock in a span of 40 generations."

Earlier, others were asking questions about aquaculture on Canada's west coast.

In September 1997, the David Suzuki Foundation and the Sierra Legal Defence Fund released a leaked B.C. government report claiming that salmon-farm pens create "a zone of death" in surrounding waters. The report also suggests Atlantic salmon from fish farms are reproducing in B.C. streams. Suzuki Foundation executive director Jim Fulton said this was "potentially devastating" for Pacific salmon, because the Atlantic species could displace threatened native stocks, especially coho and steelhead.

Many accused Mr. Fulton of exaggerating the potential danger, although B.C. Report wrote that "Scientists have long admitted that Atlantic salmon could spread disease to local stocks. They emphasize, however, that Atlantic salmon have never spawned anywhere outside their natural range despite deliberate attempts to transplant the species (experiments in B.C. date back to the 1920s)."

One solution is to seal off salmon farms from the ocean. In one operation on the U.S. west coast, salmon are raised in floating pools sealed-off from surrounding waters. Wastewater is filtered before being pumped back into the sea. At other farms the salmon have been removed from the ocean entirely; they are being raised in tanks on land. Operations such as these are more expensive to build and to operate, but critics of the industry acknowledge they are a step in the right direction. But, not everywhere.

When fish farmers fill artificial ponds enough fresh water can be slurped up to create a shortage.

In 1994 Thailand produced 250,000 tonnes of shrimp by aquaculture. To do this it created so many freshwater ponds that in places the water table fell by four metres in just two years.

Aquatic Network - http:// www.aquanet.com/

Canadian Aquaculture Industry Association - http:// www.aquaculture.ca/

Canadian Centre for Fisheries Innovation - http:// www.mi.mun. ca.ccfi/

FIRST WORLD APPETITES

Aquaculture has the potential to feed a lot of hungry people. Unfortunately, many aquaculture projects in the developing world are raising high-value species, such as salmon and shrimp, for export. Fish farms in Third World countries are often pressured to do this to earn hard currency from First World nations, so the poorer states can pay off their debts. The New Scientist reports that "This bias means that cheaper fish that could be sold to local markets often never make it into large-scale culture."

The threat to local food supplies gets worse. About half the area now used for shrimp ponds in Thailand's Inner Gulf was once used to grow rice.

FACT FILE

New Scientist magazine reported in 1997 that "Already, one in every five fish destined for dinners worldwide comes from farms."

Aquaculture is the world's fastest-growing food industry.