um its 12 liters not 12 gallons? If thats the case I think your limitted to a few small fish then, like a betta or a couple small tetras, oto cats, shrimp, or white clouds. A pleco would be too big, common plecos can get over a foot long. I have 2 small tanks with very tiny fish in them, the key is to find species that won't out grow the tank or need more room to swim. New tanks are so exciting. I wish my dorm room had more space, I'd have fishtanks everywhere. Good Luck setting it up!