because they want to swim close to the surface
I think that they will because most animals needs to be at the surface to survive and to breathe. Some of the fishes food that they eat are swimming at the surface of the water too.
By swimming
No, they are just normal swimming fishes who live in the open water.
Either you can swim, or you can't. Swimming is done close to the Surface of the water. How deep it is doesn't really matter once you can't touch bottom.
they eat tiny insects that land on the surface of the water and algae
It is caused by the magnifying effect of the glass/plastic and water.
surface soil
It's best if the water is cleaned before you close up the pool.
rocks close to the surface of the water
a cloud can be close to the surface of the water (or land). When a cloud is close to or at the surface of the water (or land) , it is called fog.
No. There can not be too much oxygen in a fishes water. If a fish is swimming upside down and it is not of a species known for doing that, then the fish has a damaged swim bladder. The fish is very sick and will die.
something with a "r"