Baby fish (as well as eggs) in a community are normally menu items for a lot of the inhabitants. Baby fish insitintively develop a hiding instinct after they are born. They know to hide. Often this may be near the bottom. But it can be in cave like places, in plants, under wood etc.
Also, many fish, when first born, do not have the shape they will acquire as they grow, angels are a good example. Usually bottom feeders look like bottom feeders from birth. However, baby fish often look drab at this stage of life and they need time to color up as they grow.
An in tank spawn will end up with more than just one baby making it, especially if there are lots of places to hide. Hitchhikers from stores tend, more often, to be singles.