Don't know if this helps but it is some interesting trivia nontheless. In the rivers and streams of Alaska we do have freshwater muscles, I was fishing for salmon with a couple of bushbred AK women and we were catching hundreds. I had noticed that many had strange clearish, dics of membrane on their gill plates. One of the gals had been working on her thesis for YEARS and explained that they were muscles(baby) from the ocean that hitch hike on the salmon. She had been working for years on their life cycle and how they got here.
Native alaskans had described harvesting muscles to survive on in some of the cultures - little was known about what they were describing. This gal was amazing in her knowledge and how she had finally discovered their reseeding. Any who, they also can piggy back back to salt water with the salmon and/or just with the current. I'm hundreds of miles inland but I'm just amazed when I find a colony of them - amazing to think of the journey it takes to get here!!!
ALASKA