Sphaerichthys osphromenoides CANESTRINI, 1860

Chocolate Gourami

Classification

Order: Perciformes Family: Osphronemidae

Distribution

Type locality is given simply as ‘Indies’ by Canestrini but this is by far the most widely distributed species in the genus being native to much of Peninsular Malaysia, Sumatra, and Borneo. In the latter records exist from throughout the Malaysian state of Sarawak and Indonesian province of West Kalimantan (Kalimantan Barat).

It’s also known from Singapore though this population may now have been extirpated. Some populations exhibit differences in colouration, particularly in the unpaired fins which may appear more blueish or reddish depending on population, and/or fin morphology, with males of some forms possessing more deeply-forked caudal and/or more extended dorsal and anal fins.

Habitat

Mostly inhabits peat swamps and associated black water streams though is also found in some clear water habitats. The former are located in forested areas and contain water that is typically stained dark brown by humic acids and other chemicals released from decaying organic material.

This results in a negligible dissolved mineral content and the pH can drop as low as 3.0 or 4.0. The dense rainforest canopy above means that very little light penetrates the water surface and the substrate is normally littered with fallen tree branches and rotting leaves.

The clear water habitats are broadly simlar in terms of water chemistry but in many cases aquatic vegetation grows profusely and often includes representatives of genera such as Cryptocoryne, Blyxa, Barclaya, Eleocharis, Utricularia, and Lymnophila.

At habitat #1 in the images above S. osphromenoides was collected alongside Trigonopoma pauciperforatum, Luciocephalus pulcher, and Nandus nebulosus, while at habitat #2 sympatric species included Rasbora einthovenii, Boraras maculatus, Belontia hasselti, Betta waseri, B. tussyae, B. imbellis, and Kryptopterus macrocephalus.

Unfortunately due to logging, agriculture and other human activities throughout Southeast Asia vast tracts of primary forest have been altered or lost entirely. Fish habitats in affected regions have also been heavily-modified in many cases with species diversity declining as a result.

Maximum Standard Length

40 – 50 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 60 ∗ 30 cm or more is suitable for a group.

Maintenance

Provided adequate cover and structure is available this species is unfussy with regards to décor with ceramic flowerpots, lengths of plastic piping and other artificial materials all useful additions. A more natural-looking arrangement might consist of a soft, sandy substrate with wood roots and branches placed such a way that plenty of shady spots and caves are formed.

The addition of dried leaf litter (beech, oak or Ketapang almond leaves are all suitable) would further emphasise the natural feel and with it the growth of beneficial microbe colonies as decomposition occurs. These can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves will aid in the simulation of a blackwater environment. Leaves can be left in the tank to break down fully or removed and replaced every few weeks.

This species seems to do best under fairly dim lighting and plant species from genera such as Microsorum, Taxiphyllum, Cryptocoryne, and Anubias are recommended since they will grow under such conditions. A few patches of floating vegetation to diffuse the light even further may also prove effective.

It naturally inhabits sluggish or still environments therefore filtration, or at least water flow, should not be very strong. Very large water changes are best avoided if the parameters are not close with 10-15% weekly adequate provided the tank is lightly-stocked.

Water Conditions

Temperature: 26 – 31 °C

pH: Wild specimens will require a value within the range 4.0 – 6.5 in order to thrive, but tank-raised individuals are normally more adaptable.

Hardness: 0 – 54 ppm for wild fish, up to 10° if captive-bred.

Diet

Chiefly a micropredator feeding on small aquatic crustaceans, worms, insect larvae and other zooplankton.

It can be a little picky in the aquarium and initially may not accept dried or otherwise prepared foods, though in many cases will learn to take them over time. At any rate it should be offered daily meals of small live or frozen fare such as Artemia nauplii, Daphnia, grindal worm, micro worm, etc., in order to develop ideal colour and conditioning.

Behaviour and CompatibilityTop ↑

Tankmates must be chosen with care since this species is slow-moving and will easily be intimidated or outcompeted for food by larger/more boisterous tankmates. Peaceful, pelagic cyprinids such as Danionella, Microdevario, Trigonostigma, or smaller Rasbora species make good choices as do some loaches such as Pangio or Kottelatlimia spp. It’s not recommended to combine it with the congener S. selatanensis in order to minimise the risk of hybridisation.

Though not gregarious in the sense of schooling/shoaling fishes it does seem to require interaction with conspecifics and displays more interesting behaviour when maintained in numbers, meaning we recommend the purchase of no less than 6 individuals. Groups develop noticeable hierarchies and you’ll often see dominant individuals chasing away their rivals at feeding time or when occupying their favourite spot.

In addition, there exist observations of an intriguing behaviour in which an individual will lie on its side and allow another member of the group to mouth its body and fins. No damage has ever been noticed during these displays and neither do they seem to form part of any spawning ritual. Some have suggested it may be a method of establishing dominance between the fish but at present this can only be considered speculation.

Sexual Dimorphism

Adult males exhibit a uniformly straight lower jaw profile and an overall more acuminate head shape than females, in which the lower jaw is slightly rounded due to the presence of distensible skin that is expanded during mouthbrooding (see ‘Reproduction’).

Other characters such as possession of relatively longer/more pointed unpaired fins or more intense colours in males do not appear to be applicable in all cases. This may be related to geographic variance, i.e., collection locality but this remains unconfirmed at present.

Reproduction

Historically there has been some confusion surrounding this species‘ method of reproduction with some sources listing it erroneously as a bubblenester or paternal mouthbrooder when it is by all accounts a maternal mouthbrooder. This is intriguing since this species and S. selatanensis are the only anabantoids in which the female broods the eggs, with all other mouth-brooding relatives having evolved a paternal strategy.

It can be bred in a group or single pair in a set-up as suggested above, and provided the quality of both water and diet is maintained should not prove too difficult. Courtship is normally initiated by the male, or alpha male if multiple individuals are present, and nuptial behaviour can be recognised by an individual taking on a darker, almost greyish patterning, while receptive females intensify in colouration, becoming a deep chocolate brown with the light vertical bars appearing golden.

The climactic spawning embrace is similar to that seen in Luciocephalus and Parasphaerichthys species in that the pair remain almost upright, rather than the female being turned upside down as in Betta and most other anabantoid genera. The spawning process may take several hours with eggs laid and fertilised on the substrate and the female collecting them in her mouth directly. The surrounding area is defended by both fish throughout.

Brooding females tend to take refuge in a quiet area of the tank and eat very little, if at all. The eggs/fry are retained in the mouth for 7 – 20 days before 10-40 fully-formed, free swimming juveniles are released. The female can be removed to a separate tank a few days post-spawning in order to minimise the chances of fry predation if you prefer though in mature, heavily-decorated set-ups some may survive. Alternatively the fry can be removed as they are released/spotted provided water of the same chemistry and temperature is available elsewhere.

The fry should be large enough to accept live foods such as microworm or Artemia nauplii immediately, and daily water changes of around 10% of tank volume should also be performed in order to maintain water quality and growth rate. The rearing tank must have a tightly-fitting cover (some breeders use clingfilm/shrinkwrap to ensure no gaps) as they need access to a layer of warm, humid air to ensure proper development of the labyrinth organ.

NotesTop ↑

The genus Sphaerichthys currently comprises four species with S. osphromenoides by far the best known in the hobby. It’s easily distinguishable from the congeners S. vaillanti and S. acrostoma since both exhibit a notably more elongate head and body profile, reverse sexual dimorphism (females being more colourful/strongly-patterened than males) and are paternal mouthbrooders.

S. selatanensis is more similar and was originally described as a subspecies by Vierke (1979), though it’s been considered a species in its own right since the late 1980s. The two differ in the number of dorsal fin rays (9-10 in S. osphromenoides vs. 7 in S. selatanensis), anal-fin rays (8 vs. 7), pls the eye is relatively smaller in S. osphromenoides.

Athough colour pattern is comparable S. selatanensis possesses an additional light, vertically-orientated bar on each flank originating just anterior to the dorsal-fin and terminating posterior to the ventral fins. In S. osphronemoides this bar is absent or reduced to a small spot anterior to the dorsal-fin.

Sphaerichthys species are often grouped within the Osphronemid subfamily Luciocephalinae along with the genera Trichogaster, Trichopodus, Luciocephalus, Parasphaerichthys, and Ctenops. They share with the latter trio an egg structure that is unique among teleosts; the distinguishing factor consisting of a series of spiralling ridges on the outer surface. This has given rise to the (as yet unproven) theory that the four genera form a monophyletic group, i.e., they share a common genetic ancestor.

In Luciocephalus and Sphaerichthys the eggs are also distinctively pear-shaped suggesting that these two share even closer genetic roots, and this theory was supported in the detailed phylogenetic study published by by Rüber et al. (2006). Sphaerichthys and Luciocephalus were repeatedly found to be most closely related to one another and represent the sister group to Ctenops and Parasphaerichthys.

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

It’s formed by a modification of the first gill arch and consists of many highly vascularised, folded flaps of skin. The structure of the organ varies in complexity between species tending to be more well-developed in those inhabiting particularly oxygen-deprived conditions.

References

1. Britz, R. and M. Kottelat, 2002 - Ichthyological Exploration of Freshwaters 13(3): 243-250
   Parasphaerichthys lineatus, a new species of labyrinth fish from southern Myanmar (Teleostei: Osphronemidae).
2. Britz, R., M. Kokoscha, and R. Riehl, 1995 - Japanese Journal of Ichthyology 42(1): 71-79
   The anabantoid genera Ctenops, Luciocephalus, Parasphaerichthys and Sphaerichthys as a monophyletic group: evidence from egg surface structure and reproductive behaviour.
3. Ng, H. H. and H.-H. Tan, 1999 - Zoological Studies 38(3): 350-366
   The fishes of the Endau drainage, Peninsular Malaysia with descriptions of two new species of catfishes (Teleostei: Akysidae, Bagridae).
4. Roberts, T. R., 1989 - Memoirs of the California Academy of Sciences 14: i-xii + 1-210
   The freshwater fishes of western Borneo (Kalimantan Barat, Indonesia).
5. Rüber, L, R. Britz and R. Zardoya, 2006 - Systematic Biology 55(3): 374-397
   Molecular phylogenetics and evolutionary diversification of labyrinth fishes (Perciformes: Anabantoidei).
6. 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.
7. Vierke, J., 1979 - Aquarium Aqua Terra 13(122): 339-343
   Beschreibung einer neuen Art und einer neuen Unterart aus der Gattung Sphaerichthys aus Borneo.