What is the proper way to brine fish? My query is regarding fish in general and specifically types like salmon, tuna and trout.


How long should fish be brined for? Some recipes say 4 hours and others say 8-12 hours. 
Should the saline solution be 6% as usual.  
How do you know if it has bined properly?  Do you expect it to be plump and juicy as with poultry or how exactly?


Thanks

To answer your question, my goal in brining is to simply get as much salt as possible into the cells of the fish. . I do not care about taste, flavour or anything else, I just want salt to penetate into all parts of the fish.  As you know if you want salt in your meat brining is the best method and better then normal and slow cooking which do not absorb to the same extent and in the same way.
It depends on why you're brining. I don't smoke fish so longer brining may be warranted for that use. I brine to keep fish juicy coming off the grill. For this I agree with Cook's illustrated:

We found that, for up to six 1-inch-thick steaks or fillets, the optimum concentration was a 6 percent brine (5 tablespoons of salt dissolved in 2 quarts of water) and the ideal time was 15 minutes. It worked no matter the species, improving the texture of the fish without over seasoning....
And brining works a lot faster on fish because the structure of muscle in fish is different than that in meat: Instead of long, thin fibers (as long as 10 centimeters in meat), fish is constructed of very short (up to 10 times shorter) bundles of fibers.