The
stream catfishes are
family Akysidae of
catfishes.
Distribution and habitat
Akysids are known from across a large area in
Southeast Asia.
They are found in the fresh waters.
Fish of the subfamily Parakysinae are primarily found in the
Malay Peninsula,
Sumatra,
Sarawak, and western and southern
Borneo.
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; 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 to a
clade formed by
Sisoridae,
Erethistidae, and
Aspredinidae.
Description
Akysids are small to minute fishes with
cryptic colouration, tiny eyes, and completely covered with unculiferous plaques or
tubercles. 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.
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 rakers and
lateral line 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.
