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Fish species (how we divide fish)

Within the aquarium hobby, we use many different systems to divide fish into practical groups. Scientists use the taxonomic system created by Carolus Linnaeus in the 18th century, and understanding the basics of this system is very helpful for hobby aquarists as well since it makes it easy to see which fish species that are closely related to each other. Using the scientific names of fish instead of common names can also prevent a lot of misunderstandings since many popular aquarium species have been given a long row of different common names and the exact same common name can also be attributed to several different species.

In addition to Linnaeus taxonomy system, you can encounter a lot of other ways of grouping fish within the hobby. In this article, we will take a brief look at some of these other divisions as well.

Taxonomic division of fish

Living organisms are divided into Domains, Kingdoms, Phylums or Divisions, Classes, Orders, Families, Genera and Species. In some cases, Subphylums/Subdivisions, Subclasses, Suborders and Subfamilies are used as well. The immensely popular Neon tetra (Paracheirodon innesi) is for instance classified as follows:

Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Genus: Paracheirodon
Species: innesi

The full species name of the Neon tetra is Paracheirodon innesi because the full species name of an organism always consists of genus name species name. This makes it easy to see where a particular species fit into the classification system.

Marine, freshwater and brackish species

Keeping a marine aquarium is very different from keeping a freshwater aquarium. Generally speaking, marine aquariums will require more experience and equipment and be more expensive to setup and maintain than freshwater aquariums, but there are naturally exceptions to this rule. Brackish aquariums are more similar to freshwater aquariums, and keeping a brackish aquarium is not consider more difficult than keeping a freshwater aquarium.

When purchasing fish, it is very important to investigate if it prefers fresh, brackish or marine conditions. This might seem like a redundant tip, but the truth is that many fish shops intentionally or unintentionally mislabel fish species. A marine species can for instance be sold as a brackish species to attract more potential buyers, because quite a few marine species can survive for at least a period of time in brackish water. It is also fairly common to sell certain brackish species as “brackish or freshwater” even though keeping them in freshwater is known to weaken their immune system in the long run.

Before you purchase a fish, always seek unbiased information about its true preferences so that you can house it in conditions that will make it thrive instead of just barely survive. Some species should only be kept within a very specific salinity range, while others are highly adaptable and can adjust to a broad salinity spectrum. There can also be significant differences within the same species; a certain geographical population can for instance have adapted to a life in a mangrove forest while another population is strictly marine. It should also be noted that preferences and adaptability can change as the fish matures and conditions that were ideal for your juvenile specimens might be unsuitable for them as adults.

Tropical vs. coldwater

Within the aquarium hobby, we often talk about tropical fish and coldwater fish. Tetras, clownfish and Central American cichlids are just a few examples of commonly kept tropical species, while goldfish and koi are some of the best known examples of coldwater species that we house in aquariums and ponds. These are very broad categories and you should always seek more specific information about the species you intend to keep and find out their exact temperature requirements before you make a purchase. A fish that hails from the tropics but lives deep down in the ocean can for instance be used to fairly cold conditions, and fish living in a small puddle on the African savannah will typically be used to much warmer water than marine species living off the coast of Madagascar even though they both come from the tropics. You should also keep in mind that planet Earth consists of more climate zones than simply tropical and non-tropical; it is commonly divided into arctic, temperate, subtropical, and tropical zones and each of these zones consists of several different smaller climate divisions.

A few words about cichlids and cichlid groups

Fish of the family Cichlidae in the order Characiformes are commonly referred to as cichlids. This is one of the largest and most diverse families of fish and it contains a lot of popular aquarium species. The family is currently comprised of 10 different subfamilies and over 200 genera, but among aquarists it is more common to group cichlids based on geographical origin and habitat. Hobbyists typically divide cichlids into three main groups: African cichlids, Central and North American cichlids, and South American cichlids.

The African cichlids can be further divided into Great Rift Valley cichlids and Other African cichlids. (Cichlids from the Great Rift Valley region are much more common in the hobby than species hailing from other parts of the continent.) Great Rift Valley cichlids are divided into four subcategories based on which lake (or lake region) they live in: Lake Malawi cichlids, Lake Tanganyika cichlids, Lake Victoria cichlids, and Other Great Rift Valley cichlids.

Dwarf cichlids are sometime counted as a special cichlid group, but all dwarf species belong to a geographical group as well.

Source: AC Tropical fish.

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