Marine aquarium fish species are much more difficult to deal with in the aquarium than freshwater varieties. Many species will be completely incompatible and , necessitate the careful selection of species when choosing which fish to include.
When choosing fish species, their compatibility with other tank occupants such as mollusks, arthropods, plants, and most importantly, corals must be considered.
The Octopus makes an excellent pet, but should be left in a dedicated 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.
An aquarium is a glass-sided container in which water-dwelling plants and animals (usually fish) are kept in captivity.
The keeping of fish in an aquarium became a popular hobby during the twentieth century, with many species of fish being caught and transported from the tropics before it was discovered how to breed them.
The major technological hurdle was the introduction of CO2 gas into the fish tank, both to control algae, and to provide carbon for the growth of the aquatic plants.