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Betta imbellis LADIGES, 1975

Crescent Betta

Classification

Osphronemidae

Distribution

Described from ‘wetlands in the area surrounding Kuala Lumpur’, and occurs naturally in southern (peninsular) Thailand, Peninsular Malaysia, and northern Sumatra.

Populations from different localities tend to exhibit differences in colouration and patterning, and if the locality of wild fish is known, they’re often labelled as such by collectors and enthusiasts in order to maintain accuracy and preserve pure bloodlines eg. Penang Island, Tiak/Perak, Batang Berjuntai/Selangor, Sepang/Selangor, etc.

Introduction of ornamental forms and other Betta spp. is known to be having an adverse effect on the purity of some wild populations, the species having been heavily line-bred for aggression in southern Thailand, where it’s used in organised bouts in the same way as B. splendens elsewhere, and for the aquarium hobby, with many different strains available. It’s also been introduced elsewhere, with feral populations now established in Singapore, for example.

Habitat

Inhabits still and sluggish waters, including rice paddies, swamps, roadside ditches, streams and ponds. These are often shaded by submerged, surface or marginal vegetation and sometimes contain little dissolved oxygen. Water conditions tend to vary and change rapidly during the annual monsoon season. Substrates can vary from leaf litter to mud, sand, or deep sediment.

While most populations inhabit freshwaters some are found in brackish coastal swamps.

Maximum Standard Length

50 – 60 mm.

Aquarium SizeTop ↑

An  aquarium with base measurements of 45 ∗ 30 cm or equivalent is large enough for a pair.

Maintenance

This species does best in a well-planted, shady tank with plenty of surface cover in the form of tall stem plants, floating types such as Salvinia or Riccia spp. or tropical lilies from the genus Nymphaea. Cryptocoryne spp. are also a good choice and will cope with the dim conditions.

Driftwood can also be used and other plants such as Microsorum or Taxiphyllum spp. can be attached to it. Small clay plant pots, lengths of plastic piping or empty camera film cases can also be included to provide further shelter.

The addition of some dried leaf litter (beech, oak or Ketapang almond leaves are all suitable) is also recommended. In addition to offering additional shelter for the fish it brings with it the establishment of microbe colonies as decomposition occurs. These microorganisms can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves are also thought beneficial.

As it naturally inhabits sluggish waters filtration should not be too strong, with an air-powered sponge filter set to turn over gently adequate. Keep the tank well-covered and do not fill it to the top as like all Betta spp. it requires occasional access to the layer of humid air that will form above the water surface, and is an excellent jumper.

Water Conditions

Temperature24 – 28 °C

pH5.5 – 7.5

Hardness0 – 268 ppm


Diet

Likely to prey on insects and other small invertebrates/zooplankton in nature. Captive fish will normally accept dried products once they’re recognised as edible, but should be offered plenty of small live or frozen foods such as DaphniaArtemia or bloodworm regularly to ensure development of optimal colour and condition. Take care not to overfeed as Betta spp. seem particularly prone to obesity.

Behaviour and CompatibilityTop ↑

Not recommended for the standard community set-up for reasons already touched upon. It’s requirements and disposition mean it’s best kept alone or with very peaceful species since much bigger or more vigorous fishes are likely to intimidate and outcompete it.

Some small cyprinids and loaches that inhabit similar environments in nature are compatible, but the presence of any other fishes can be a distracting influence should a pair decide to spawn.

Provided with sufficient cover and broken lines-of-sight it’s possible to keep more than one male per tank, though it’s best to isolate pairs for breeding purposes in most cases.

Sexual Dimorphism

Males are more colourful and develop more-extended fins than females.

Reproduction

Bubblenester. Organise a separate tank for breeding purposes unless the fish are already being maintained alone, setting this up as suggested above.

The tank should have the tightest-fitting cover you can find (some breeders use clingfilm instead to ensure no gaps) as the fry need access to a layer of warm, humid air without which development of the labyrinth organ can be impaired.

The pair need not be separated prior to spawning. The male may construct the nest in a tube or canister, under a broad plant leaf or among fine-leaved surface vegetation, and will not usually tolerate the female in the vicinity until it’s complete.

Just prior to spawning the body colour of the female pales and dark bars appear on the flanks, with the act itself normally occurring below the nest in an ‘embrace’ typical of osphronemids, with the male wrapping himself around the female. At the point of climax milt and a few eggs are released which the female proceeds to catch between pelvic fins and body.

The male then transfers them to his nest while the female recovers any that fell. This cycle is then repeated until the female is spent of eggs, a process that can take some time.

Post-spawning the adults can normally be left in situ although the female is no longer actively involved with the male assuming sole responsibility for guarding and tending the nest.

The eggs hatch in 24-48 hours, remaining in the nest for a further 3-4 days until the yolk sac is fully-absorbed, while the male continues to collecting and return any that fall. If threatened the entire nest may be moved elsewhere. Once the fry begin to swim freely the male will lose interest, but the adults do not usually eat their offspring.

The fry will require an infusoria-type food for the first few days, after which they should be large enough to accept  microworm and Artemia nauplii immediately, though it should be noted that there exist reports of young Betta developing health issues if fed excessive amounts of the latter.

Offer small amounts of different foods 2 -3 times per day for optimal growth rate, and don’t change too much water at once, with regular, small changes preferable to intermittent larger ones.

This species has been hybridised with domesticated B. splendens, B. smaragdina and the undescribed B. sp. ‘Mahachai’ and selectively line-bred for the aquarium trade, leading to the development of a number of colour forms that do not occur naturally.

NotesTop ↑

B. imbellis is included in the Betta splendens complex of closely-related species within the genus, of which members share the following set of characters: head length short 22-31 % SL; often a brightly-coloured body; iris of the eye with iridescent green or blue patches; body elongate or slender; opercles parallel when head viewed dorsally; caudal-fin rays red or brown and contrasting with the iridescent interradial membranes; unpaired fins without an iridescent margin; opercle with red or blue vertical bars in males; dorsal-fin rays 0-II, 7-9; anal-fin rays II-V, 21-26.

The unique combination of characters distinguishing B. imbellis from others in the group is as follows: base body colour dark brown to black; opercle with iridescent blue scales; fins iridescent blue; no transverse bars in caudal-fin; caudal-fin with red, crescent-shaped distal band; posterior anal-fin rays coloured red distally.

The genus Betta is the most speciose within the family Osphronemidae with almost 70 recognised members and looks set to grow further with new ones continuing to be described on a regular basis since the turn of the century.

Member species have successfully adapted to inhabit a variety of ecological niches from stagnant ditches to flowing hill streams including some extreme environments such as highly acidic peat swamp forests.

The referral of members to a number of groups containing closely-related species is now generally accepted but largely based on morphological/behavioural characters. Molecular phylogenetic work is thus required and would undoubtedly prove useful in more precisely determining relationships between these fishes.

A full list of the species groups as currently recognised can be found here.

Like others in the suborder Anabantoidei this species possesses an accessory breathing organ known as the labyrinth. So-called due to its maze-like structure this organ allows the fish to breathe atmospheric air to a certain extent.

Comprising paired suprabranchial organs formed via expansion of the epibranchial (upper) section of the first gill arch and housed in a chamber above the gills, it contains many highly-vascularised, folded flaps of skin which function as a large respiratory surface. Its structure varies in complexity between species, tending to be better-developed in those inhabiting harsher environments.

References

  1. Ladiges, W., 1975 - Aquarien und Terrarien-Zeitschrift (8): 262-264
    Betta imbellis nov. spec., der Friedliche Kampffisch.
  2. Tan, H. H. and P. K. L. Ng, 2005 - Raffles Bulletin of Zoology Supplement 13: 115-138
    The labyrinth fishes (Teleostei: Anabantoidei, Channoidei) of Sumatra, Indonesia.
  3. Tan, H. H. and P. K. L. Ng, 2005 - Raffles Bulletin of Zoology Supplement 13: 43-99
    The fighting fishes (Teleostei: Osphronemidae: Genus Betta) of Singapore, Malaysia and Brunei.

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