Know nothing about fish - help me ID what I saw?

Hiya,

I have never kept fish because I until 2 years ago I lived at home and my mum had a huge phobia of them! As a result, I never really paid them much attention. But recently I was at the pet shop to buy food for my other pets and saw these really cute bottom-feeding fish amongst the others in the tanks. I've tried googling a few different bottom-feeding fish keywords but I'm not sure what they were... would anyone mind giving me an overview of the sorts of bottom feeding fish that are commonly available?

Also... out of curiosity, because I really did like them - do you need a whole ecosystem of fish or can you keep a specific type, like these little guys? I'm totally new for this, so any links or general tips really welcome thanks!