Interesting news from British Columbia Canada indicates that kokanee salmon can become sockeye salmon given the opportunity. Kokanee salmon are landlocked sockeye, spending their lifecycle in freshwater migrating from lakes upstream to spawn. Sockeye are much larger and migrate from the ocean to fresh water.
I had always thought that speciation had occurred between these fish, and while that still may be the case it looks as if kokanee (at least those found in Alouette lake) have retained their ability to live in salt water. This has implications for the potential to restore previously destroyed salmon runs. This is based on the news that kokanee released inadvertently during an opening of a dam on Alouette Lake have returned as Sockeye. Granted these kokanee had only been land locked for not even a century but it may have implications for other salmon runs that have been interrupted for longer periods. Unfortunately the information I was able for find did not discuss this in an evolutionary context, which would be the most interesting aspect of this story to myself.