The scariest thing is that nobody seems to be considering the impact on those wild fish of fish farming on the scale that is now being proposed on the coast of Norway or in the open ocean off the United States. Fish farming, even with conventional techniques, changes fish within a few generations from an animal like a wild buffalo or a wildebeest to the equivalent of a domestic cow. Domesticated salmon, after several generations, are fat, listless things that are good at putting on weight, not swimming up fast-moving rivers. When they get into a river and breed with wild fish, they can damage the wild fish's prospects of surviving to reproduce. When domesticated fish breed with wild fish, studies indicate the breeding success initially goes up, then slumps as the genetically different offspring are far less successful at returning to the river. Many of the salmon in Norwegian rivers, which used to have fine runs of unusually large fish, are now of farmed origin. Domesticated salmon are also prone to potentially lethal diseases, such as infectious salmon anemia, which has meant many thousands have had to be quarantined or killed. They are also prone to the parasite Gyrodactylus salaris, which has meant that whole river systems in Norway have had to be poisoned with the insecticide rotenone and restocked.

— Charles Clover

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