Vegetarian fish

It's a different story for fish that eat plants.

According to the Nature study, the vast majority of animals grown on fish farms thrive on diets consisting primarily of plant food. These include vegetarian finfish - such as carp, catfish, tilapia and milkfish - as well as scallops, oysters and other filter feeders.

These species, which are popular in many cultures around the world, require only minimal amounts of fishmeal in their diet and consequently do very little damage to wild fish stocks - unlike carnivorous shrimp or salmon.

Therefore, according to Naylor and Mooney, species raised on vegetarian diets actually contribute to the world's supply of fish.

But that could change dramatically, warn the authors, if certain trends continue - especially in Asia, which accounts for roughly 90 percent of global aquaculture production.

Asian farmers produce more than 10 million tons of carp and tilapia every year.

But as human populations increase and land becomes scarce, there is less space available to build ponds for carp, tilapia and other popular plant-eating fish. So Asian farmers have decided to grow bigger fish by adding extra amounts of fishmeal to existing ponds.

The result, say the authors, could mean a dramatic increase in the demand for fishmeal, putting even more pressure on herring and other ocean fisheries.

Indirect costs

In addition to depleting wild fish populations, aquaculture also causes indirect harm to the environment, according to the Nature study.

"Many fish farms damage coastal ecosystems through habitat destruction," says Naylor.

She notes that hundreds of thousands of acres of mangrove forests and coastal wetlands throughout Asia have been transformed into milkfish and shrimp ponds. The consequence has been a devastatin
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
28-Jun-2000