The moniker "bumblebee" is very often applied to catfishes with a pattern of alternating brown and yellowbands encircling the body. Thus have the South American Microglanis, the African Microsynodontis, and the Asian Pseudomystus been given this name (these catfishes have nothing in common except for their color pattern, which are vaguely similar). This article will provide a brief overview of yet another group of catfishes for which the name "bumblebee catfishes" seems apt: the miniature Asian catfishes of the genus Akysis Bleeker, 1858.
Many species of Akysis possess the color pattern for which their chosen name is apt, but there are also many other species that have a more irregular, blotchy color pattern. Externally, Akysis species look like any other regular (albeit somewhat small) catfish, save for the rough, tuberculate skin. The genus is distributed throughout Southeast Asia, being particularly diverse on the Indochinese peninsula (i.e. mainland Asia between India and China). In the mid-1990s, there were only 11 species of Akysis known to science, since then, the number has more than doubled to 29 species (this includes 5 more species whose descriptions are currently in press).
Fig. 1. Heads in members of the pseudobagarius species group (left) and the variegatus species group (right), Arrows indicate differences in mouth position and spacing of anterior and posterior nostrils (see text). Figure modified from Ng & Kottelat (1998).
Akysis species can be divided into two species groups (following Ng & Kottelat, 1998): the pseudobagarius species group (14 species), and the variegatus species group (15 species). The two species groups can be distinguished as follows: members of the pseudobagarius group have a relatively elongate body, a more inferior mouth (i.e. located on the underside instead of at the anterior end of the head; Fig. 1), relatively large anterior and posterior nostrils that are separated only by the base of the nasal barbel (Fig. 1), and a strongly forked caudal fin; members of the variegatus group have a shorter and deeper body, a more terminal mouth (i.e. located at the anterior end of the head instead of the underside; Fig. 1), relatively small anterior and posterior nostrils that are separated by a space between the anterior nostrils and the base of the nasal barbel (Fig. 1), and an emarginate or truncate caudal fin. A list of Akysis species with their known distributions is given below:
Members of the pseudobagarius species group:
- A. alfredi Ng & Kottelat, 1998: Pahang River drainage in Peninsular Malaysia
- A. baramensis (Fowler, 1905): Baram River drainage in Borneo
- A. filifer Ng & Rainboth, 2005: Mekong River drainage in Cambodia
- A. fuscus Ng & Kottelat ,1996: Kapuas River drainage in Borneo
- A. hardmani Ng & Sabaj, 2005: Chao Phraya River drainage in Thailand
- A. inermis Ng & Kottelat, 2000: Mekong River drainage in Laos and Cambodia
- A. leucorhynchus Fowler, 1934: Chao Phraya and Tapi River drainages in Thailand
- A. macronemus Bleeker, 1860: Musi and Batang Hari River drainages in Sumatra
- A. meridionalis Ng & Siebert, 2004: Barito River drainage in Borneo
- A. nitidus Ng & Rainboth, 2005: Mekong River drainage in Laos
- A. pseudobagarius Roberts, 1989: Kapuas River drainage in Borneo
- A. similis Ng & Kottelat,1998: Mekong River drainage in Vietnam
- A. sinensis He in He & Chen, 1981: Mekong River drainage in China
- A. subtilis Ng & Kottelat, 1998: Mekong River drainage in Thailand
Members of the variegatus species group
- A. brachybarbatus Chen in He & Chen, 1981: Mekong River drainage in China
- A. clavulus Ng & Freyhof, 2003: Cai and Duc My rivers, draining to the central coast of Vietnam
- A. clinatus Ng & Rainboth, 2005: southwest Cambodia
- A. ephippifer Ng & Kottelat, 1998: Mekong River drainage in Laos and Cambodia
- A. fuliginatus Ng & Rainboth, 2005: Mekong River drainage in Cambodia
- A. hendricksoni Alfred, 1966: northern Peninsular Malaysia and southern Thailand south of the Isthmus of Kra
- A. heterurus Ng, 1996: Batang Hari River drainage in Sumatra
- A. maculipinnis Fowler, 1934: southwest Cambodia and southeast Thailand
- A. microps Ng & Tan, 1999: Endau River drainage in Peninsular Malaysia
- A. pictus Günther, 1883: Salween River drainage in Myanmar
- A. prashadi Hora, 1936 : Irrawaddy River drainage in Myanmar
- A. recavus Ng & Kottelat, 1998: Chao Phraya River drainage in Thailand
- A. variegatus (Bleeker, 1846): Java
- A. varius Ng & Kottelat, 1998: Mekong River drainage in Laos and Thailand
- A. vespa Ng & Kottelat, 2004: Ataran River drainage in southern Myanmar
Akysis can be found in a wide variety of habitats, ranging from hillstreams to large rivers, and even estuaries. The one thing in common in areas where they have been collected is the presence of the fine substrate, be it the form of sand or mud. The habitats they have been collected in also have a considerable current, which means that they are fishes that require adequate oxygenation. They can be found hiding around tree stumps and fallen logs where leaves and twigs accumulate, amongst leaf litter, in patches of submerged vegetation such as Cryptocoryne, or in riffle areas under stones and coarse gravel (Ng & Tan, 1999; Ng & Freyhof, 2002). In the aquarium, they show a tendency to burrow into the substrate and remain there for most of the day, something that they most likely do in the wild. When they swim, they do so close to the substrate in short quick bursts from one place to another.
Fig. 2. Akysis clavulus has a blotchier color pattern.
Fig. 3. The color pattern of A. heterurus is still blotchy, but begins to resemble the familiar bumblebee pattern.
These diminutive (largest recorded size ca. 5 cm SL) catfish are predatory in nature and many specimens of Akysis hendricksoni regurgitated small atyid shrimps of the genus Caridina after capture (Ng, 1996). In the aquarium, they will readily take bloodworms and other small live or frozen food.
In some of the species, sexual dimorphism is present (Ng & Kottelat, 1996; Ng & Tan, 1999): males have shorter pelvic fins located further away from the anal fin. The pelvic fins of the males are also more closely-set and curved to form a bowl. The use of the pelvic fins in the male remains unknown. They may be used for handling eggs or for directing the sperm towards the eggs (Ng & Kottelat, 1996). The eggs produced by Akysis species are relatively large for such small fish, with reported sizes ranging from 0.8 mm in A. fuscus (see Ng & Kottelat, 1996) to 1.5 mm in A. vespa (see Ng & Kottelat, 2004).
Akysis species are not often exported for the aquarium trade. In my personal experience, one is only likely to encounter A. heterurus, A. leucorhynchus, A. pictus or A. prashadi. With adequate decor and water conditions, they are not difficult to maintain in the aquarium, and can even be induced to breed (as has been done for A. vespa).
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