A
marine aquarium is an
aquarium that keeps
marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only (
FO), fish only with
live rock (
FOWLR), and
reef aquaria. Fish only tanks often showcase large or aggressive marine fish species and generally rely on mechanical and chemical filtration. FOWLR and reef tanks use
live rock, a material composed of coral skeletons harboring beneficial nitrogen waste metabolizing bacteria, as a means of more natural biological filtration.