Steelchromedome said: In the ocean, teleosts (bony fish), such as salmon, which includes steelhead, drink copious amounts of water and urinate minimally while freshwater teleosts drink very little and urinate profusely.
When, in the past, I have drank a lot of beer, I have soon enough had to eliminate all that beer or burst. Unless the guzzler fish can pee out his sides, it just doesn't work.
Sorta goes against physics, that last part of yours - something from nothing. Tough logic stream to follow, unless fish are sponges I suppose. What, the one with the dry mouth absorbs the fluids through his body, only to pee it out normal style, but in excess volume?
As to the fish movement from salt to fresh and its journey upstream, I do believe there is a degree of acclimation that takes place, but I also believe they loiter until a freshet of fresh water is added to the stream flow - and assurance of sufficient flow to support their migration over potential barriers to passage and to provide protection from airborne predators. But then I am but an old pimp daddy, and not a bio-man with fish scales adorning his work outfit, and I've never had the pleasure of interviewing any anadromous fish so as to get their take on the issue.