You might wonder what a bunch of deep sea marine fish are doing in a freshwater catalog and the reason is they are included for the reason that they are the oldest fishes, and when modern fish evolved into what they are today, they came from these or something very similar. When fish first became fish, that is they evolved past something not-a-fish and the transition from worm to eel like thing but not a fish to a fish took ages. But these, as far as we know, are the oldest living relative of the first fish found in those primordial seas.