Why do ecologists seem to give the nod to farmed catfish and tilapia but not salmon?

Farming Fish
C. Clairborne Ray, New York Times 12 Apr 10;

Q. Why do ecologists seem to give the nod to farmed catfish and tilapia but not salmon?

A. The ecological issues related to fish farming vary from freshwater to saltwater fish; from carnivorous species to noncarnivores; and from open pens to closed ponds and tanks, among many other factors.

Farmed salmon, often raised in pens that are permeable by surrounding ocean waters and fed a diet rich in fish meal and fish oil, have been of special concern to critics like the World Wildlife Fund. Besides citing the risk of pressure on the rest of the fish world to provide food for the farmed salmon, the fund lists potential problems including fecal pollution, contamination with antibiotics, the transfer of diseases and parasites to wild fish, and competition and crossbreeding with wild species.

The farming of salmon in European coastal ocean waters was also the subject of an often-cited review article published in 1987 by the Scottish researchers R. J. Gowen and N. B. Bradbury. They raised the issue of the concentrated release of waste food and excretory products into surrounding waters and discussed ways of mitigating resulting problems. Other critics say that farmed salmon threaten consumers with contaminants like PCBs from their feed.

Farmed catfish and tilapia raise far fewer such issues, because they require no fish or animal components in their feed and thrive in enclosed freshwater tanks, ponds or channels.

Innovative techniques are being studied for reducing many of the potential risks of all kinds of fish farming.

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