No sooner had we started fretting about the risk of mad cow disease in our hamburgers than a new report indicated that the salmon raised on fish farms were laced with far more toxic chemicals than their wild brethren.

Just what this may mean for human health is murky, given that the risk appears to be small and the health benefits of eating salmon, whether farm-raised or caught in the wild, are thought to be considerable.

But the message to fish farmers, the dominant suppliers of salmon in this country, was unmistakably clear: stop feeding your penned-up salmon the fish meal that seems to be causing the problem.