Fish(es), Minerals, Train Tracks and Parks (and the law of Constructive Taking)
If you give a man a fish, you feed him for a day. If you teach a man to fish, you feed him for a lifetime. But what if a man has the right to sell fish, and he builds his business and livelihood around that right, and then the government passes a law allowing only the government to sell fish, putting him out of business? In a nutshell, that's the backdrop for a 1979 Supreme Court of Canada SCC decision called Manitoba Fisheries Ltd. v. The Queen.
Source: bennettjones.com