Anyone who is saying that "humans are fish" is saying something really rather silly. Humans are humans, fish are fish, apes are apes, millipedes are millipedes.
Now, as it happens, this human was born into a "white, anglo-saxon, protestant" family. I remain white, and essentiallly anglo-saxon, but protestant is something I can do without. My father was likewise born into a white, anglo-saxon, protestant family, and that's how he identified, as did his father, his grand-father and great-grand-father -- I can go back 7 generations from me, to about 1740. BUT, what if I could go back 20 generations? Well, there were no protestants then, so I suppose it would be catholic. And 100 generations ago, there were no Catholics, or even Christians. Nor were there Anglo-Saxons. So what would my grandsire of 100 generations ago be?
Well, I don't know. I cannot even be sure he would have been white. And 500 generations ago, he would have definitely been black and in Africa!
No, a human is not a fish, but somewhere in his very distant list of ancestors was a fish. And long before that, a single-celled something. As Pooh Bah says, in the Gilbert & Sullivan operetta the Mikado, "Don't mention it. I am, in point of fact, a particularly haughty and exclusive person, of pre-Adamite ancestral descent. You will understand this when I tell you that I can trace my ancestry back to a protoplasmal primordial atomic globule." Silly, I know, but surely you can see the point.