An aquarium dweller is an aquatic animal that lives in a contained environment, such as a fish tank. Common aquarium dwellers include the tetra (5 letters), a small freshwater fish; the ALGA (4 letters), a type of seaweed; the guppy (5 letters), a brightly colored fish; the EEL (3 letters), a long, snake-like fish; the GOLDFISH (8 letters), a popular pet fish; the SKATE (5 letters), a flat fish; and the gourami (7 letters), a tropical fish.