Beginners will want to stick with a simple species like the damselfish or clownfish (also know as the anemonefish). Species such as dragonets and lionfish should be avoided by beginners and those with small marine tanks. When choosing species, not only must one consider what other fish are in the tank, but also other occupants such as mollusks, arthropods, plants, and ,most importantly, corals.
There are several species that should be avoided altogether. These include batfishes, sharks, rayss, and seahorses.
Octopuses make excellent pets, but should be left in a species tank without any fish. They must also be prevented from climbing out of the aquarium, since they are very strong and can survive a remarkably long time outside the water.