>>12192047It could be freshwater, anon. The main support for the idea comes from the fact that most of the basally branching groups of living fish live in freshwater, and from looking at how fish osmoregulate.
The first argument is deceptive, since it misses that these groups all have make fossil records. Relict populations survive in lakes and rivers, just like they do islands. As for the other argument I don't really remember how it goes. Haven't studied vertebrate physiology in years.
