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.
Marine fishkeeping is different from its freshwater counterpart because of the fundamental differences in the constitution of saltwater and the resulting differences in the adaptation of its inhabitants. A stable marine aquarium requires more equipment than freshwater systems, and generally requires more stringent water quality monitoring. The inhabitants of a marine aquarium are often difficult to acquire and are usually more expensive than freshwater aquarium inhabitants. However, the inhabitants of saltwater aquariums are usually much more spectacular than freshwater aquarium fish.
Marine reef aquarium at the London aquarium
Marine fishkeeping history
The first saltwater tanks were Venetian glass jars where the Romans kept anemones outdoors, but these systems were very short lived. The first personal saltwater fishkeeping began on a wider scale in the 1950s, starting with the basic rectangular glass aquariums (usually 20 gallon), still popular today. Bleached coral along with a substrate of coarse crushed coral were the norm. Algae, including beneficial types such as coralline algae, were viewed negatively and were generally removed. The clean, sterile tank was viewed as the healthiest.
The Aztec Empire had 10 ponds of saltwater aquariums at Texcoco.
During the early days of marine aquaria, saltwater was collected at local beaches. Natural saltwater contains many unwanted organisms and pollutants. Aquarium literature of the time suggests that the most commonly kept marine fish were the percula clownfish, sergeant major damselfish, small, brackish-water pufferfish and scats, jeweled blennies, and blue damsels. Aquariums were equipped with large air compressors, and were heavily aerated and filtered (primarily with undergravel filters, a norm for some time).
An ever-growing number of hobbyists experiencing the inconvenience of gathering natural sea water and the concurrent development of analytical chemistry techniques led to research into the chemical composition of sea water. Synthetic salt mixes were developed to replicate the chemical environment of the tropical ocean, including trace elements and salts. This advance made marine fishkeeping popular in areas without access to clean sea water.
Air driven, counter-current protein skimmers and reliable submersible electric heaters were invented in Germany. Various advances in filtration included trickle and hang-on filters, both allowing a more natural equilibrium in the aquarium environment. The advancement of fluorescent lighting technologies to provide higher output, along with metal halide lighting, enabled the first reef tanks, making it possible to keep corals and other invertebrates without natural sunlight.
More efficient chemical testing allowed aquarists to understand the chemical properties of aquariums. By the 1980s, a biologically-based understanding of how to maintain an artificial ocean environment brought more successful and widespread marine fishkeeping.
Marine aquarium components
The major components are an aquarium, usually made from glass or acrylic, filtration equipment, lighting, and an aquarium heater. Marine aquariums can range in volume from less than 80 litres, (< 20 US gal) to over 1,200 litres (300 US gal). Small volumes are more difficult to maintain due to the more rapid changes in water chemistry. The majority of saltwater aquariums are between 160 and 400 litres (40 and 100 US gal).
Nano reef aquarium maintained at home
Types of marine aquariums
Marine aquarists typically divide saltwater aquariums into those housing fish only, those housing fish with live rock, and those primarily designed to house corals and other invertebrates (also known as reef aquariums). Many fish hobbyists also divide the types of saltwater tanks based on the water temperatures at which they are kept.
The most common type of saltwater fish tank, the tropical marine tank, houses marine animals from tropical climates. Usually kept between 24 to 28 °C (75 to 82 °F), these tanks include tropical reef tanks, as well as fish-only tanks. These tanks tend to have a low concentrations of microscopic plankton and other foods eaten by filter feeders. Most livestock for these aquariums are acquired through commercial means.
Temperate marine (coldwater marine)
A temperate marine aquarium
One of the more obscure types of fish tanks, the coldwater marine tank, holds fish of temperate climates, with temperatures ranging around 10 to 24 degrees Celsius (50–75 °F). While most of these tanks are not as aesthetically pleasing as their tropical counterparts, colorful species such as dahlia anemones and the ornate cowfish can be found. However most coldwater fish are gray or dull in color. Most colorful species are found in the western pacific. These tanks also tend to require extra skill to maintain.
Since coldwater cnidaria are rare and coldwater corals only occur at great depths, hobbyists are largely confined to fish, crustaceans and mollusks. Since there are very few commercially available coldwater fish, hobbyists usually have to physically acquire specimens. The most common way of doing this is by trolling or seining. Unlike commercially available tropical fish, whose behavior patterns and tank compatibilities are well documented, coldwater fish require much local ichthyology knowledge in order to maintain them.
Many temperate fish have specific local diet requirements, while others, like tautog (blackfish), will eat just about any crustacean or frozen foods. The blackfish should not be kept with crabs and mollusks, while other fish, like the oyster cracker toadfish, will do fine with any fish that is not small enough to fit into its mouth. Due to it being such a localized hobby, not many people go the route of local tanks. However, they are more cost-effective than reef tanks, cheaper and easier to maintain, and the fish hardier. It takes experience before one can successfully gage the compatibility of the fish in one’s area.
Almost all species kept in marine aquaria at this time are caught in the wild, although tank-raised specimens are becoming increasingly common as a viable alternative. Only a few species such as clownfish are captive-bred on a commercial scale. Much collecting is done in Indonesia and the Philippines, where use of cyanide and other destructive collection methods, while discouraged, is unfortunately common. The majority of live rock is also harvested in the wild, and recent restrictions on this harvest in Florida have caused a shift to Fijian and aquacultured rock. Natural rock, because it is created by coral polyps, takes many years if not centuries to form, and is a vital habitat for countless marine species; thus, commercial-scale harvesting of naturally-occurring live rock has been criticized by conservationists. Additionally, many animal species sold to hobbyists have very specific dietary and habitat requirements that cannot be met by hobbyists (e.g. Labroides genus wrasses, the moorish idol); these animals almost inevitably die quickly and have markedly reduced lifespans compared to wild specimens. Often these specific environmental requirements cause improperly housed lifestock’s color and appearance to be poor. These issues are often downplayed by individuals and organizations with a financial interest in the trade. Hobbyists who support conservation should buy only certified net-caught fish (although ensuring the legitimacy of such claims can be difficult) or captive-raised fish, as well as farmed corals and to support legitimate reef conservation efforts. The majority of corals can be “fragged”, whereby a portion of a larger captive coral is separated and can subsequently be raised into an individual specimen, allowing for coral propagation within the domestic aquarium; the trade in frags (i.e. fragments) offers a fantastic opportunity for marine aquarists to obtain new and unique corals while limiting the impact on the natural environment. Rare species and those without a history of being successfully kept in captivity should be avoided.
Various businesses have commercialized fishkeeping. With the advent of large scale business operations focusing on breeding massive quantities of specimens, marine fishkeeping has become much more widespread than ever before. Perhaps the biggest disincentive to marine fishkeeping, in comparison to freshwater, is the initial setup cost. A 100 US gallon (400 L) reef tank full of coral and equipment can cost in excess of $2,500 US, although a budget-minded home hobbyist could spend less than half of this and still get a satisfactory result.