The longfin escolar, ''Scombrolabrax heterolepis'', also known as the black mackerel, is a widespread but uncommon deep sea

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

that presents some difficulties for

taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

. It is placed in its own family Scombrolabracidae, but the family's placement in the

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

s of

Perciformes Perciformes (), also called the Percomorpha or Acanthopteri, is an order or superorder of ray-finned fish. If considered a single order, they are the most numerous order of vertebrates, containing about 41% of all bony fish. Perciformes means ...

has included

Scombroidei Scombroidei is a suborder of the Perciformes, the largest order of fish. The suborder includes the barracuda, tuna, and mackerel, as well as the billfish The term billfish refers to a group of saltwater predatory fish characterised by pro ...

Percoidei Percoidei is one of 3 suborders of bony fishes in the order Perciformes. Many commercially harvested fish species are considered to be contained in this suborder, including the snappers, groupers, basses, goatfishes and perches. Divisions The ...

, and Trichiuiroidei, while some authors place it in its own suborder Scombrolabracoidei and even in its own order the Scombrolabraciformes. The fish bears some resemblance to members of

Gempylidae The Gempylidae are a family of perciform fishes commonly known as snake mackerels or escolars. The family includes about 25 species. They are elongated fishes with a similar appearance to barracudas, having a long dorsal fin, usually with one or ...

, but has protrusible

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

e, serrated

opercle The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

s and

preopercle The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

s, and a spur on the lowest principal caudal ray, all of which are characteristic of percoids. Its color varies from black to dark brown. This fish is known to grow to 30 cm in length. The body is covered in soft scales which easily slough off when handled. The eyes are large with usually a single pair of elongated teeth in the middle of the top jaw. The longfin escolar is unique among fishes for having several of its

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e hollowed out and filled by

evagination Endodermic evagination relates to the inner germ layers of cells of the very early embryo, from which is formed the lining of the digestive tract, of other internal organs, and of certain glands, implies the extension of a layer of body tissue to f ...

s of the

gas bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth w ...

. It is most often encountered as a bycatch species in pelagic longline fisheries.

References

* * * * J. S. Nelson, ''

Fishes of the World ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

''. {{Taxonbar, from=Q1754834 Scombrolabracidae Fish described in 1921