Large freshwater bottom dwelling species include: rays, eels, plecos, loaches and catfish. AquariumDomain’s Large Freshwater Bottom Dwellers section focuses on these larger or “monster” species of bottom dwellers that reach very large sizes and require large aquariums to properly house. Larger bottom dweller species are very popular with many intermediate to advanced freshwater aquarium hobbyists that enjoy the beauty and challenge of keeping these unique fish species.