The Indian Vagabond Butterflyfish, Chaetodon decussatus, is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of butterflyfish

Butterflyfish

The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera...

 (family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Chaetodontidae). It is found in the Indo-West Pacific, from the Maldives

Maldives

The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...

 via India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Sri Lanka

Sri Lanka

Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

 and the Andaman Sea

Andaman Sea

The Andaman Sea or Burma Sea is a body of water to the southeast of the Bay of Bengal, south of Burma, west of Thailand and east of the Andaman Islands, India; it is part of the Indian Ocean....

 to the westernmost portion of the Indonesia

Indonesia

Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

n archipelago.

Growing to a maximum of 20 cm (nearly 8 in) long, it is found on rich coral reef

Coral reef

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...

s and also on rubble and rocky areas. The monogamous adults swim in pairs and may be territorial

Territory (animal)

In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...

 and aggressive to other Chaetodon

Chaetodon

Chaetodon is a tropical fish genus in the family Chaetodontidae. Like their relatives, they are known as "butterflyfish". This genus is by far the largest among the Chaetodontidae, with about 90 living species included here, though most might warrant recognition as distinct genera.Several subgenera...

; juveniles are solitary. The Indian Vagabond Butterflyfish feeds largely on algae and coral polyps. They are oviparous.

It belongs to the large subgenus

Subgenus

In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...

 Rabdophorus which might warrant recognition as a distinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

. In this group, it almost certainly is a rather close relative of the Threadfin Butterflyfish

Threadfin butterflyfish

The Threadfin Butterflyfish, Chaetodon auriga, is a species of butterflyfish . It is found in the Indo-Pacific region from the Red Sea and eastern Africa to the Hawaiian, Marquesan, and Ducie islands, north to southern Japan, south to Lord Howe Island and Rapa Iti, at depths of between 1 and 35...

 (C. auriga) and the Vagabond Butterflyfish

Vagabond butterflyfish

The Vagabond Butterflyfish, Chaetodon vagabundus, is a species of butterflyfish . It is found from the Red Sea and off East Africa as far east as the Tuamotu Islands, north to southern Japan and south to the Austral Islands....

 (C. vagabundus). C. decussatus might be closer to the Threadfin Butterflyfish than to the common Vagabond Butterflyfish; as C. vagabundus has yielded abnormal DNA sequence

DNA sequence

The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

data this is hard to say however. The C. auriga species group shares the characteristic pattern of two areas of ascending and descending oblique lines; species differ conspicuously in hindpart coloration.