The stream catfishes are 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...

 Akysidae of catfish

Catfish

Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

es.

Distribution and habitat

Akysids are known from across a large area in Southeast Asia

Southeast Asia

Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

. They are found in the fresh waters. Fish of the subfamily Parakysinae are primarily found in the Malay Peninsula

Malay Peninsula

The Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...

, Sumatra

Sumatra

Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

, Sarawak

Sarawak

Sarawak is one of two Malaysian states on the island of Borneo. Known as Bumi Kenyalang , Sarawak is situated on the north-west of the island. It is the largest state in Malaysia followed by Sabah, the second largest state located to the North- East.The administrative capital is Kuching, which...

, and western and southern Borneo

Borneo

Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

. Most species are generally found in deeper parts of relatively swift rivers and forest streams.

Taxonomy

It includes at least 42 species in five genera

Genera

Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...

; many species are only recently described. The family is divided into two subfamilies, Akysinae and Parakysinae. Parakysinae has previously been listed as an independent family.

This family is sister

Cladistics

Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

 to a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 formed by Sisoridae

Sisoridae

Sisoridae is a family of catfishes . These Asian catfish live in fast-moving waters and often have adaptations that allow them to adhere to objects in their habitat.-Taxonomy:...

, Erethistidae

Erethistidae

Erethistidae are a family of catfishes that originate from southern Asia.-Taxonomy:This family includes species previously placed in Sisoridae. They were removed because they were thought to be more closely related to the neotropical Aspredinidae than to the remaining sisorids due to a number of...

, and Aspredinidae

Aspredinidae

The Aspredinidae are a small South American family of catfishes also known as the banjo catfishes.-Distribution:Aspredinids are found throughout the major tropical rivers of South America...

.

Description

Akysids are small to minute fishes with cryptic colouration, tiny eyes, and completely covered with unculiferous plaques or tubercle

Tubercle

A tubercle is generally a wart-like projection, but it has slightly different meaning depending on which family of plants or animals it is used to refer to....

s. In some genera some of the tubercles on the body are enlarged and arranged in distinctive longitudinal rows, the number of which may be diagnostic. The dorsal fin has a strong spine and a short base, and there are usually four or five soft rays. There are four pairs of barbels

Barbel (anatomy)

A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...

. Unusually among catfish, they have a low principal caudal fin ray count and more rays in the upper caudal fin lobe than the lower.

In Akysinae, the body is with small unculiferous tubercles arranged in longitudinal rows, a median middorsal row and usually four lateral rows. The dorsal fin with usually five soft rays. An adipose fin is present and moderate. The pectoral fin has a strong spine, and the anterior margin is with a notch visible dorsally and usually serrated posteriorly. The gill openings are relatively narrow and the eyes are small.

In Parakysinae, the dorsal fin has four soft rays. The pectoral fin spine is nonserrate. The anal fin is with 8–13 soft rays. The mandibular barbels are usually with short accessory barbels. Gill raker

Gill raker

Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...

s and lateral line

Lateral line

The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

 pores are absent. The head and body are covered with rounded tubercles arranged in longitudinal rows in Acrochordontichthys and Breitensteinia or evenely distributed in Parakysis. The adipose fin is absent in Breitensteinia and Parakysis and is present as an adipose ridge; the fin is present and long in Acrochordontichthys. The eyes are minute. There are 30–32 vertebrae.