Well, it depends on the type you have... I'm no expert, but I do know that fish don't actually 'sleep'. Half their brains shut down at a time in order for them to get oxygen and keep themselves from getting in trouble. I also heard that a fish has to move to keep in their intake of oxygen, so of course, this helps prove the 'half the brain sleeping at a time' factor. In fact, fish are a lot like dolphins and whales which do the same thing... I mean, if you have an algae-eater, like I do, it might sit at the bottom of the tank without moving for like 20 minutes... I have to repeatedly tap the side to make sure it's not dead. However, I'm not too sure if your fish can 'sleep at the bottom of the tank'... if it doesnt move, or start turning upside down, then it's probably dead... you can tell by their eyes, too (which would be glazed).
fish dont actually sleep; they have no eyelids. scientists dont know for sure but they think that they go into a state of rest. It can be hard to tell if a fish is sleeping; they might float motionless, float on bottom of tank or hide in tank decor.
Its probably sleeping.
they are at the bottom of the tank,and are very still. you can see their eyes,but they are just sleeping.
if your fish is going around the tank with its eyes cosed multiple times.
The white fins wont be moving and they will be at the bottom of the tank
they just settle at the bottom of fish tank
The only bottom feeding fish I know of is a catfish. They are kinda cool depending on how your tank looks and if your fine with less bright colors.
a fish, since it is in the water, and has no eyelids, would float underwater in place, with its eyes open. this is unlike the shark, who needs to constantly keep swimming to stay up in the water because it does not have air bladders to keep it up. if the shark were to stop swimming, it would immediately sink to the bottom. thank you very much for reading my answer.
gravel
I suggest that you learn more about your fish in your aquarium. One of your fish might be a bottom sucker which means that they eat all of the dirt on the side or bottom of your tank. If one of your fish are bottom suckers, that's probably the reason why your aquarium is clean. If none of your fish are bottom suckers, than somebody must be secretly cleaning your tank for you.
It dies
Fish eggs, fish sperm, mold.