Taxonomy & naming
Desmopuntius rhomboocellatus was originally described by Koumans in 1940. Its nomenclatural history reflects the turbulent taxonomy of Southeast Asian barbs: the species was at times placed in Systomus and spent many decades in the catch-all genus Puntius under the combination Puntius rhomboocellatus. Kottelat's landmark 2013 catalogue of Southeast Asian inland waters fishes reorganised the old Puntius complex into a suite of smaller, more natural genera; rhomboocellatus was assigned to Desmopuntius, a genus of small to medium-sized Sundaic barbs with spotted or ocellate patterning.
The Catalog of Fishes (Eschmeyer, CAS) records the current valid combination as Desmopuntius rhomboocellatus (Koumans, 1940), the parenthetical authority indicating the original description was in a different genus. Aquarium literature and older trade sources may still list this fish as Puntius rhomboocellatus.
Morphology
Desmopuntius rhomboocellatus reaches approximately 3.5 in total length. The body is moderately deep and laterally compressed in the typical barb fashion. The ground colour is pale silvery to yellowish, and along the flanks runs a row of dark, diamond or rhombus-shaped blotches — the ocelli that define the species' name. These markings can appear as solid dark spots or as outlined ocellar patches depending on the individual and its condition.
The fins are generally hyaline to lightly pigmented. As in most Desmopuntius species, there is mild sexual dimorphism: females tend to become noticeably rounder and more deep-bellied when gravid, while males are somewhat slimmer.
Habitat
This species is native to West and Central Kalimantan, the Indonesian portion of Borneo. Its core habitat is the peat swamp forest and blackwater stream systems of lowland Sundaland — some of the most acidic, ion-poor freshwater in the world. In the wild the water is stained dark amber with dissolved humic and fulvic acids leached from decomposing peat, and pH values below 4.0 are documented for such systems.
Temperature in these lowland tropical habitats is warm year-round, broadly in the range of 73–82 °F per FishBase. Conductivity is extremely low and hardness minimal; the water is very soft. Sunlight is often filtered through a dense forest canopy, and the substrate is typically dark organic peat or leaf litter. This is a highly specialised environment, and the species' preference for soft, acidic conditions is correspondingly strong.
Feeding
Desmopuntius rhomboocellatus is a micropredator. In its natural peat-swamp habitat it forages on small invertebrates including insects and their larvae, worms, crustaceans, and zooplankton, supplementing this with any other small organic matter available in the water column and at the surface.
In the aquarium it accepts a wide variety of prepared and live foods. High-quality micro-pellets and flake are a practical staple, but the fish responds well to regular offerings of live or frozen bloodworm, daphnia, brine shrimp, and similar small invertebrate fare. Variety in the diet promotes good colour and condition.
Mating
Like all barbs, Desmopuntius rhomboocellatus is an egg-scattering, non-guarding spawner. No pair bond is formed and no nest or territory is maintained beyond brief courtship interactions. When a female is gravid and conditions are right, a male pursues her through fine-leaved vegetation or along the substrate, the two pressing briefly together to release eggs and milt simultaneously.
Multiple males may compete to drive a single female. Colour intensity and activity in males peaks during courtship. The adhesive eggs are scattered among plants or settle onto the substrate and are subsequently ignored — or actively consumed — by the adults.
Breeding
Desmopuntius rhomboocellatus can be bred in the aquarium with attention to water chemistry. Conditioning the fish with live and frozen foods ahead of a spawning attempt improves success. A separate breeding vessel with very soft, acidic water — mimicking the peat-swamp environment — fine-leaved plants or a spawning mop, and a layer of mesh or marbles on the bottom to protect eggs from predation by the parents is the standard approach.
Spawning typically follows shortly after introduction of well-conditioned fish into the prepared tank. The adults should be removed after spawning to prevent egg predation. Eggs hatch in approximately 24–48 hours depending on temperature, and the larvae become free-swimming a few days later. First foods are infusoria or very fine powdered food, transitioning to newly hatched brine shrimp as the fry grow. There is no parental care at any stage.
In the aquarium
The snakeskin barb is an appealing but somewhat specialised aquarium fish, best suited to a keeper who can provide the soft, acidic conditions it requires. Seriously Fish notes that while the species tolerates a modest pH range in captivity (4.0 and above), its natural habitat sits well below pH 4.0 in the wild, and the fish thrives when housed in water that at least approximates those soft, humic conditions. Hardness should be low; the FishBase figure of up to 15 dGH represents a ceiling rather than an ideal.
It is a schooling species and should be kept in groups of at least eight to ten individuals, which encourages natural behaviour and reduces any tendency toward shyness. Tankmates should be chosen from other soft-water, acid-tolerant species that inhabit similar Sundaic blackwater environments. The tank itself benefits from tannin-staining via dried leaves or peat filtration, subdued lighting, and planting with species tolerant of acidic conditions. The fish is peaceful and does not bother robust tankmates, though it should not be housed with very small or delicate species.
Conservation
Desmopuntius rhomboocellatus is assessed as Least Concern (LC) on the IUCN Red List, with the most recent evaluation completed in 2020. The species has a reasonable distribution across West and Central Kalimantan, and no evidence of a range-wide decline sufficient to warrant a threatened category was found at the time of assessment.
Nonetheless, the peat-swamp and blackwater habitats that this species depends on are among the most threatened freshwater ecosystems in Southeast Asia. Kalimantan's lowland peat forests have been extensively cleared and drained for palm oil plantations, timber extraction, and agricultural conversion, destroying the waterlogged, acidic conditions on which species like this barb rely. Fire — both accidental and deliberate — has further degraded vast tracts of peat swamp across Borneo. Long-term monitoring of the species' range and habitat quality will be important as development pressure on Kalimantan's remaining lowland forests continues.