There is a whole, fascinating science to river and stream structure, and with so many implications for understanding how these structures and mechanisms affect fish population, occurrence, behavior, and ecology, it's well worth studying for aquarium interpretation! Leaf litter beds form in what stream ecologists call "meanders", which are stream structures that form when moving water in a stream erodes the outer banks and widens its "valley", and the inner part of the river has less energy and deposits silt- or in our instance, leaves. Did you get that part where I mentioned that the lower-energy parts of the water courses tend to accumulate leaves and sediments and stuff? It's logical, right? And it's also interesting, because, as we know, fishes and their food items...
After a lifetime in the hobby, I tend to find myself continuously drawn to fishes which, at first glance, aren't all that rare, or even "challenging" to keep...yet, somehow are seldom kept in conditions which they have adapted to live under for eons. Here's a favorite example: Everyone knows the Neon Tetra, Paracheirodon inessi. It's a strong candidate for the title of "Official fish of the Aquarium Hobby!" This fish is inescapable...almost universally recognized by even non-aquarium-hobbyists. Of course, there other members of the genus Paracheirodon which hobbyists have become enamored with, such as the diminutive, yet equally alluring P. simulans, the "Green Neon Tetra." Topping out at around 3/4" (about 2cm) in length, it's certainly deserving of the hobby moniker...