The threespine stickleback lives in Lake Washington and over the last 50 years the fish has changed from a soft-skinned fish to a partial or full body armor fish. The fish has now revered back to its saltwater armored origins. Apparently this change is due to a mutation that occurred after the lake was cleared of pollution. “A program started in the late 1960s to clear the lake of toxic sludge made the sticklebacks de-evolve.”

More precisely, according to PhysOrg “when the lake was polluted, the transparency of its water was low, affording a range of vision only about 30 inches deep. The tainted, mucky water provided the sticklebacks with an opaque blanket of security against predators such as cutthroat trout, and so the fish needed little bony armor to keep them from being eaten by the trout.
In 1968, after the cleanup was complete, the lake's transparency reached a depth of 10 feet. Today, the water's clarity approaches 25 feet. Lacking the cover of darkness they once enjoyed, over the past 40 years about half of Lake Washington sticklebacks have evolved to become fully armored, with bony plates protecting their bodies from head to tail.”

Here is yet another example of what we might not have discovered has someone not had the patience to watch a particular fish in a particular lake for 50 years! Here's the link to the original article for more details. http://www.physorg.com/news130073255.html

Pamela Alexander-Beutler