Taxonomy is the practice and science of classification.

It is composed of two greek words, taxis (order,arrangement) and nomos (law or science), hence the word literally means "Science of arrangement".

The first attempts to classify fish began in ancient world, the first recorded work is in Indian text known as “Kautila’s Arthasastra” belonging to period about 321 BC..

These were very detailed descriptions, like “Pirthuroman”which means a fish with long hairs, i.e barbels near snout.
Around 246 BC King Asoka had pillars erected throughout India, these pillars had vital information inscribed on them.
Many of them had descriptions of various animals including fish. Some example are:

1. Anathikamacchi- boneless fish (sharks)
2. Vedaveyake- eluding grasp (Eels)
3. Kaphatasayake-sleep feigning fish (puffer fish).

Hippocrates and Atistotles from around 384-322 BC from Greece are two other pioneers who developed animal classification.

There have been changes is the classification system, however the system proposed by Carl Linne (Linnaeus) is followed till today.

He proposed what is called bi nominal nomenclature, naming every living thing with a two part name, the first one based on genus(plural genera) and second part on species (same in singular or plural).

This system again saw a major change with Charles Darwin’s publication “The origin of Life”in 1859.

His theory of evolution meant that species placed together in a genus were assumed to have had a common origin, a concept that underlies all important subsequent classifications of fishes and other organisms Current System.

The current system is based on classifying living beings into separate divisions called “Taxon”or “Taxa”in plural. Hence the term Taxonomy.

Each level of this classification is called a “Rank”.

The classification used today must confirm to “International Code of Zoological Nomenclature” which is administered by International Commission on Zoological Nomenclature based at “Natural History Museum”in London

The highest rank is called “Kingdom.

There are five kingdoms currently recognized, Monera,Protista, Plantae, Fungi, and Animalia.

All animals are grouped under kingdom “Animalia” The lowermost in case of animals is “Species”, there is one more level below called “Subspecies”.

There are other lower categories in case of plants like variants etc, but these are not used in case of animals.

.

Species: Species is the keystone of taxonomic study. This is because it is the only rank that can be collected, observed and studied.

It is always written in two parts, the first part always starts with a capital letter and signifies “Genus”, second part always start with a letter in small caps.

Both parts are always written in italics. Thus the name Labidochromis caeruleus, refers to “Labidochromis” which is the genus and the second part “caeruleus,”refers to the species.

Subspecies: This is below the rank of species and is expressed in 3 parts.

Species and subspecies are described on the basis of specimens which are called type specimens. These specimens are stored carefully and so that they can be studied by future generations.

Specimens briefly can be of two types, Primary and secondary :

Primary types are

• Holotypes: When a species is described on the basis of single specimen it is called holotype.
• Neotype: Sometimes a replacement of primary is permitted only when there is strong evidence that the original primary type specimen was lost or destroyed and when a complex nomenclature problem exists that can only be solved by the selection of a neotype.

Secondary types are Para types, additional specimens used in the description of a new species.

Genus: Genus or Genera(plural) is the taxonomic rank just above species.

It might include a single species or group of species presumably of common phylogenetic(sharing a common evolution relationship) origin which is separated from other units by a decided gap.

In some case there are sub categories also called “sub genus”.

Genus forms the first part of name of a species. It always starts with a capital letter and the first letter is always capitalized.

There might be many species in a genus or there can be a single species also.

Family: Family are a taxonomic rank including one or more genera of common phylogenetic origin which is separated from other units by a decided gap.

Family consists of number of similar genera in most cases, sometime a single genus can form a family due to its peculiarities like genus Chaetobranchus in family Acestrorhynchidae.

All families end with words ‘idea’.

Order: Order are a taxonomic rank including one or more family.

They may consist of number of similar families in most cases, however sometime a single family can form an order due to its peculiarities like family Amiidae in order Amiiformes.

Sometimes a genus may be placed directly under a order with any family or any other category in between like genus Conorhynchos under order Anguilliformes

All order end with words ‘formes’.

Class It is a sub divison of Phylum Phylum It is one of the major taxonomic ranks used in classification of animals.

Phylum One of the major used in of ranks used in classification of animals