> where the fresh water fish came from. genomes are funny things, sometimes they can be set up with weak points, prone to breakage, sometimes bracketing a big

> where the fresh water fish came from. genomes are funny things, sometimes they can be set up with weak points, prone to breakage, sometimes bracketing a big section with a bunch of genes that when broken out, has a hard time figuring out which way it goes back in, might get it backwards in which case the individual born has the genes but not "correctly" ordered, they are not going to have a great life and likely get eaten as slow poke runts. But it keeps happening anyway. In 1964 there was a _very_ big earthquake in Alaska[1] extents of the seafloor were raised 30 feet out of the water and remain dry land today. In the process a number of lakes and ponds are formed of the seawater that did not make it out and gradually become fresher with the rain water runoff over time. By conventional wisdom any individual ocean going fish trapped in these ponds is doomed but the ponds are populated now with freshwater Stickleback [2]. Which seems kinda "too soon" for random isolated ponds unless birds were planting them or something. But no, it is the large genetic inversion that forms a for the most part, a sufficient single switch to thrive in fresh or salt water depending on how it is thrown. [3] The salt water fish survived in their doomed environment long enough to spawn enough offspring that the ones with the inversion that would have been the losers were now the fittest. So in answer to when did the fresh water fish show up? Probably immediately and we don't even need to evoke the old hedge "in geological time frames" [1] https://en.wikipedia.org/wiki/1964_Alaska_earthquake https://en.wikipedia.org/wiki/1964_Alaska_earthquake [2] https://en.wikipedia.org/wiki/Stickleback https://en.wikipedia.org/wiki/Stickleback [3] https://www.sciencedaily.com/releases/2015/12/151214165724.htm https://www.sciencedaily.com/releases/2015/12/151214165724.h...