Being old enough to be of the "book" generation,
I can say that many of today's fish are not new but just new versions of older species. For example, the Flame or Powder Blue dwarf gourami is not it's own specie. It's just a color morph of the regular dwarf gourami. So if you know how to keep them, you know how to keep the color morph. The list like this example is long too. What is new is the equipment used to keep fish today. That said, the basic principles of fish keeping are exactly the same as they were 50 years ago when I go started. So once you learn those principles, the method to apply them don't seem so strange or menacing.
One last thing on books, I have many that came out in the 50s, 60s and 70s ( I have the loach book posted above
) and since their publications, new fish, not new color morphs but new species, have been discovered in areas closed to exploration back then. So if you want some good more complete
fish books, you might want to look at those published after the 80s or 90s. If you are looking for books on how to keep aquariums, those older books will be as good ( if not better) than today's. I've seen some of today's and they are very abridged.