Farmed fish replacing beef in the world's diet.

I quote from an article in the current Economist:

(T)he farmed-fish industry continues to make productivity improvements. Fish farms have found crafty ways to use lower quantities of fishmeal as feed. In the early days of aquaculture, it could take up to ten pounds of wild fish to produce one pound of salmon. Now the number is down to five. That may still be an inefficient use of protein, but the ratio is set to improve further. Fish farms have also become more energy-efficient, meaning that they are less affected by higher energy prices. And they have learned how to handle diseases better, reducing the quantity of fish that ends up being unsellable. 

As a result of all these improvements, the global production of farmed fish, measured in tonnes, now exceeds the production of beef (see chart). Output is likely to continue growing: the FAO estimates that by 2020 it will reach six times its 1990 level.

Could this be a win, win, win, win situation? Farmed fish could provide an affordable source of protein for people who are trying to increase protein intake. They could provide a healthier source of protein to replace beef in the diet of people in rich countries. Fish farming could reduce pressure on land for grazing cattle. And fish farming could provide a new primary industry giving employment to large numbers of people.