Esomus metallicus AHL, 1923

Striped Flying Barb

Etymology

Esomus: from the Latin preposition e-, meaning ‘out of’, and Ancient Greek σῶμα (sôma), meaning ‘body’, presumably in reference to the extremely long maxillary barbels.

metallicus: from the Latin metallum, meaning ‘metal’, and -icus, meaning ‘belonging to’, presumably in reference to the silvery colour pattern with reflective lateral stripe.

Classification

Order: Cypriniformes Family: Cyprinidae

Distribution

Described from ‘Phet Buri’ which corresponds to modern-day Phetchaburi Province, southwestern Thailand, but currently understood to be distributed from the Salween River basin, Myanmar, eastwards across Thailand in the Mae Klong, Chao Phraya and Mekong watersheds. In the latter of which it’s also been recorded in Laos, Cambodia and Vietnam.

Also known from the Tonlé Sap lake and river system in Cambodia, peninsular Thailand and the northern tip of Peninsular Malaysia.

It’s abundant across the majority of this range with one interesting population existing on Don Khong island, the largest of the famous Si Phan Don or four thousand islands and situated in the main Mekong river channel, just below the Khone waterfalls in Champasak Province, Laos, while feral populations exist on the islands of Singapore and Borneo.

Habitat

Found in various types of habitat but shows a marked preference for shallow, slow-moving and standing waters such as rice paddies and other temporally-inundated environments. According to Rainboth (1996) it moves into these at the onset of the wet season and only returns to permanent water bodies when the flooding recedes; one study found it to be one of the three most abundant species in rice paddies of southern Laos.

It has also been collected from muddy ditches, semi-polluted canals and small streams, but is generally absent from major river channels.

Maximum Standard Length

50 – 75 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 120 ∗ 30 cm should be the smallest considered.

Maintenance

Choice of décor is not as critical as water quality although this species does look particularly effective in a well-planted tank with a dark substrate. The addition of some floating plants and driftwood roots or branches to diffuse the light seems to reduce skittish behaviour as well as adding a more natural feel.

Water movement does not need to be particularly strong as it mostly hails from sluggish waters, and do not add this fish to a biologically-immature tank as it can be susceptible to swings in water chemistry. Also be sure to add a tightly-fitting cover as it’s an accomplished jumper and able to escape through the tiniest of gaps.

Water Conditions

Temperature: 20 – 26 °C

pH: 6.0 – 7.0

Hardness: 18 – 215 ppm

Diet

Feeds on terrestrial and aquatic invertebrates and their larvae in nature. In the aquarium it will accept dried foods of a suitable size but should also be offered live and frozen Daphnia, Artemia, chironomid larvae (bloodworm), etc., on a regular basis.

Behaviour and CompatibilityTop ↑

There exist mixed reports on this species’ suitability for community aquaria. Some have observed a pronounced tendency to nip the fins of tankmates while others report no problems. Any aggressive behaviour is likely to be more pronounced when it is maintained in insufficient numbers or with slow-moving or long-finned species.

Though gregarious it’s a shoaling rather than schooling fish which develops a hierarchical pecking order. It therefore should always be maintained in a group of 8 or more since weaker individuals may be bullied incessantly if smaller numbers are kept. You’ll be rewarded with a more natural-looking display plus interesting behaviour from the fish as they interact with one another.

Sexual Dimorphism

Adult males are noticeably slimmer and usually a little smaller than females.

Reproduction

We’re unsure whether it’s been bred in captivity, although it has been induced via the use of hormones for experimental purposes.

NotesTop ↑

There currently exist a dozen described Esomus specie,s although few are seen in the ornamental trade and none are especially popular. Most are commonplace in their native countries but are generally overlooked by collectors due to their relatively plain colouration. Their most common use in some areas is actually as a feeder fish in the aquaculture of larger species. They are characterised by greatly-enlarged pectoral fins and two pairs of barbels, of which the maxillary pair are extremely long and usually reach the pectoral fins.

E. metallicus can be told apart from congeners by a combination of: two pairs barbels  of which the rostral extends past the eye, and maxillary beyond the pelvic-fin base; absence of supraorbital groove; lateral line single and incomplete, extending to the area between pelvic and anal fins; presence of lateral body stripe which is more intense posteriorly and terminates at caudal-fin base; no markings on fins.

In recent years a number of phylogenetic studies involving Esomus and its near relatives have been conducted and conflicting results published. For example a 2003 study by Fang et al. concluded that the genus is the sister group, i.e., most closely-related to, Danio whereas Mayden et al. (2007) placed the genera Chela, Microrasbora, Devario and Inlecypris as sisters to Danio with Esomus as a basal sister group to that larger clade.

A further analysis by Fang et al. published in 2009 recovered Esomus as sister to Danio but noted that its exact placement is uncertain due to conflicting results depending on the type of analysis performed. The authors go on to state that more detailed studies into the molecular and morphological characters of the genus are needed in order to identify its exact relationships with its closest relatives.

Some aquarium hobbyists have recorded a type of wasting disease that can appear in Esomus spp. characterised by a rapid reduction in body mass of affected specimens. The problem manifests itself as an initial thinning of the ventral part of the body just behind the gills and usually results in death within a couple of weeks. As yet no treatment is known.

References

1. Fang, F., 2003 - Copeia 2003(4): 714-728
   Phylogenetic Analysis of the Asian Cyprinid Genus Danio (Teleostei, Cyprinidae).
2. Fang, F., M. Norén, T. Y. Liao, M. Källersjö and S. O. Kullander, 2009 - Zoologica Scripta 38(1): 1-20
   Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae).
3. Kottelat, M., 2013 - Raffles Bulletin of Zoology Supplement 27: 1-663
   The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.
4. Mayden, R. L., K. L. Tang, K. W. Conway, J. Freyhof, S. Chamberlain, M. Haskins, L. Schneider, M. Sudkamp, R. M. Wood, M. Agnew, A. Bufalino, Z. Sulaiman, M. Miya, K. Saitoh, S. He, 2007 - Journal of Experimental Zoology, Molecular Development and Evolution 308B: 642–654
   Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species.
5. Nguyen Khoa, S., K. Lorenzen, C. Garaway, B. Chamsinhg, D. Siebert and M. Randone, 2005 - Joornal of Applied Ecology 42(5): 892-900
   Impacts of irrigation on fisheries in rain-fed rice-farming landscapes.
6. Rainboth, W. J., 1996 - FAO, Rome: 1-265
   Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes.