Sphaerichthys acrostoma VIERKE, 1979

Giant Chocolate Gourami

Classification

Order: Perciformes Family: Osphronemidae

Distribution

Known only from Indonesian parts of the island of Borneo. The type locality is within the Mentaya River drainage and presumably in Central Kalimantan (Kalimantan Tengah) province, Indonesia since it lies around 250 km northwest of Banjarmasin, the capital city of neighbouring South Kalimantan (Kalimantan Selatan).

It appears well-distributed within the Mentaya system since records exist from close to the town of Sampit, a port on the river‘s main channel some distance further south.

Habitat

Chiefly inhabits peat swamps and associated black water streams though may 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.

Aquatic plant species may include representatives of genera such as Cryptocoryne, Blyxa, Barclaya, Eleocharis, Utricularia, and Lymnophila. 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.

The type locality comprised a tannin-stained jungle stream and other species collected in the area included Betta foerschi, Parosphromenus parvulus, Hemirhamphodon chrysopunctatus, Pectenocypris korthausae, ‘Puntius‘ foerschi, and Osteochilus pentalineatus.

Maximum Standard Length

60 – 70 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 80 ∗ 30 cm or more is recommended.

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 with 10-15% weekly adequate provided the tank is lightly-stocked.

Water Conditions

Temperature: 21 – 25 °C

pH: 3.5 – 6.5

Hardness: 0 – 54 ppm

Diet

Primarily 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 Trigonostigma or smaller Rasbora species make good choices as do some loaches such as Pangio or Kottelatlimia spp..

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 the purchase of no less than 6 individuals is recommended. Groups develop noticeable hierarchies and you’ll often see dominant individuals chasing away their rivals at feeding time or when occupying their favourite spot.

Sexual Dimorphism

When in courtship or otherwise excited males exhibit a lateral stripe extending from the base of the caudal-fin to midbody, while females lack this stripe and instead possess a series of darkened scale rows in the lower anterior portion of the body and along the base of the anal-fin.

Females also possess a greater degree of red pigmentation on the throat area and in the unpaired fins, plus a uniformly straight lower jaw profile and an overall more acuminate head shape than males, in which the lower jaw is slightly rounded due to the presence of distensible skin that is expanded during mouthbrooding (see ‘Reproduction’).

Reproduction

Paternal mouthbrooder. 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 female or alpha female if multiple individuals are present.

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 male collecting them in his mouth directly. The surrounding area is defended by both fish throughout.

Brooding males 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 male 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 ↑

This species is traded under several names of which others include ‘sharp-nosed gourami’, ‘moonlight chocolate gourami’, ‘black-lined chocolate gourami’ and ‘black-tailed chocolate gourami’, though it’s far from common in the hobby. Its unique colour pattern makes it difficult to confuse with any of the three other members of the genus even in the absence of meristic data.

Specifically, S. osphromenoides and S. selatanensis both possess a relatively more compact body shape, distinctive colour pattern consisting of light vertical bars over a brown to reddish base colouration and are maternal mouthbrooders. There are also differences in the number of dorsal-fin rays between these three with 9-10 in S. osphromenoides, 7 in S. selatanensis, and 6 in S. acrostoma.

Its closest relative appears to be S. vaillanti which is similar in terms of body shape and also a paternal mouthbrooder, but the two be easily identified by colour pattern. In S. acrostoma males possess a light lateral stripe extending from the caudal peduncle base to midbody with a concurrent dark stripe underneath while females exhibit a few dark, vertically-orientated scale rows in the lower, anterior portion of the otherwise uniformly brownish body. There are two red markings extending posteriorally and ventrally to the eye, respectively.

In S. vaillanti males the pale lateral stripe extends from behind the the eye to the caudal-fin base and the concurrent dark stripe is both thinner and less intense, plus there is an additional vertical bar between dorsal and anal fins. Females possess a series of alternating red and green vertical bars extending across most of the body and usually above the lateral line, the anterior portion of the upper body is predominantly greenish with the posterior more reddish, and all colours intensify to spectacular effect when the fish are in spawning condition. The eye markings as described for S. acrostoma are darkish in both sexes.

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. Vierke, J., 1979 - Aquarium Aqua Terra 13(122): 339-343
   Beschreibung einer neuen Art und einer neuen Unterart aus der Gattung Sphaerichthys aus Borneo.
2. 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).
3. 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.
4. Rüber, L, R. Britz, and R. Zardoya, 2006 - Systematic Biology 55(3): 374-397
   Molecular phylogenetics and evolutionary diversification of labyrinth fishes (Perciformes: Anabantoidei).
5. Schaller, D. and M. Kottelat, 1989 - Aquarien und Terrarien-Zeitschrift 43(1): 31, 33-37
   Betta strohi sp. n., ein neuer Kampffisch aus Südborneo (Osteichthyes: Belontiidae).