Taxonomy & naming
Dichotomyctere ocellatus was formally described by Franz Steindachner in 1870. The specific epithet ocellatus is Latin for 'having little eyes' or 'eye-spotted', referring to the conspicuous ocelli on the caudal fin. For much of its taxonomic history the species was placed in the broad wastebasket genus Tetraodon and widely known in the aquarium literature under the combination Tetraodon biocellatus — the latter name (from the Latin bi-, 'two', + ocellatus, 'eye-spotted') explicitly describing the two caudal eyespots. A subsequent revision split the old Asian Tetraodon material: the name Tetraodon is now restricted to African species, while the Southeast Asian brackish puffers — including the green spotted puffer and the figure-eight — were transferred to Dichotomyctere. The Catalog of Fishes records the current valid combination as Dichotomyctere ocellatus (Steindachner, 1870).
The figure-eight puffer belongs to a group of brackish-estuarine Dichotomyctere species that also includes the green spotted puffer (D. nigroviridis) and the topaz puffer (D. fluviatilis). All three share a general body plan of a pale, spotted or reticulated dorsum contrasting with a white belly, but differ in the arrangement and character of the markings. The trade names 'figure-8 puffer', 'eyespot puffer' and 'eightspot puffer' all refer to the same species and are used interchangeably.
Morphology
The figure-eight puffer is a small, rotund tetraodontid reaching a maximum of about 3 in total length, with the typical body plan of the family: a roughly globose, scaleless trunk that tapers to a small caudal fin, a blunt snout with large, forward-facing eyes, and the four fused teeth of the upper and lower jaws that form a hard, parrot-like beak. The beak is divided by a median suture into two upper and two lower plates — the 'four-toothed' character that names the family Tetraodontidae.
Coloration is striking. The dorsal surface is yellow-green to olive-gold, patterned with irregular dark brown to black blotches and reticulations that continue onto the upper flanks. The ventral surface is clean white or cream. The caudal fin bears the defining mark: two dark ocelli (eyespots), usually set close together in an arrangement that reads as the numeral eight when the fin is spread, sometimes with a yellow ring around the spots. Pectoral fins are the primary propulsors; puffers swim with a characteristic sculling motion rather than using a tail-flick.
Sexual dimorphism is minimal and difficult to assess externally outside of breeding condition; females may appear slightly deeper-bodied when gravid. There are no scales; instead the skin is bare and elastically distensible to allow inflation. Small spines embedded in the skin assist in stabilising the inflated sphere.
Habitat
Dichotomyctere ocellatus is a coastal lowland species native to the tidal rivers, estuaries and mangrove fringes of Southeast Asia. FishBase records its distribution as spanning the Mekong drainage (Cambodia), Peninsular Malaysia, and parts of Borneo (Sarawak and Kalimantan), though the record is incomplete and the full range is likely wider along the Sunda shelf coastline. Like the other brackish Dichotomyctere, it inhabits the transitional zone where river outflow meets tidal influence — environments characterised by fluctuating salinity, warm temperatures and generally hard, alkaline water with high mineral content.
FishBase gives a temperature range of 72–79 °F and the species is demersal, spending much of its time near the substrate in shallow coastal habitats. Care guides consistently place it in low-end brackish conditions — a specific gravity of around SG 1.005–1.008 — somewhat fresher than the green spotted puffer, which trends toward near-marine salinity as it grows. The figure-eight therefore occupies a slightly freshwater-adjacent position within the brackish puffer guild, occasionally found in the lower reaches of tidal rivers where salinities are diluted by freshwater input.
Feeding
Dichotomyctere ocellatus is a durophage — a hard-prey specialist. Its robust, fused beak teeth are designed to crack mollusc shells and the exoskeletons of crustaceans; in the wild its diet consists primarily of snails, small bivalves, shrimp and crabs, supplemented opportunistically with worms and other invertebrates encountered on or near the substrate. This hard-prey diet is not merely preferred but physiologically necessary: the beak is composed of dentine and enamel that grows continuously, and without regular contact with hard food items the beak overgrows into a deformity that prevents normal feeding and eventually kills the fish.
In the aquarium, snails — particularly pond snails and ramshorn snails cultured as feeders — are the ideal dietary staple, delivering both nutrition and beak-wearing abrasion. Frozen or live shrimp, crayfish pieces, small mussels and other shellfish round out the diet. Soft foods (freeze-dried worms, flakes, pellets) may be accepted but should not form the bulk of the diet, as they contribute nothing to beak maintenance. Many keepers cultivate a snail colony specifically to supply their puffers on demand.
Mating
Breeding behaviour in Dichotomyctere ocellatus is not well documented in the wild, and captive spawning is rare and incompletely reported. What accounts exist describe a substrate-spawning mode: males court females with pursuit and display behaviour, and spawning takes place over a flat hard surface or the sand bottom, where demersal adhesive eggs are deposited.
Reports on parental behaviour are conflicting. Some accounts describe the male attending and guarding the egg mass after spawning, consistent with behaviour recorded in related brackish tetraodontids; others indicate no sustained parental protection. Given the scarcity and inconsistency of captive breeding records, the details of courtship triggers, egg guarding and any post-hatch male attendance in this species remain genuinely unclear. Aquarists attempting to breed the figure-eight puffer should approach the exercise with low expectations and careful documentation, as the literature is thin.
Breeding
Captive breeding of Dichotomyctere ocellatus is rarely achieved and poorly documented — far less so than for the green spotted puffer, which is also infrequently bred. The breeding mode is substrate spawning: eggs are described as adhesive and demersal, scattered on flat surfaces or sand. Where the male has been reported to guard the clutch, he is said to remain close to the egg mass until hatching; whether this is consistent or species-specific behaviour is uncertain given the limited data.
Fry, when they hatch within a few days, are very small and require infusoria-grade first foods before graduating to small live prey such as newly hatched brine shrimp. Water quality management is critical; the fry are sensitive. No established or reliable breeding protocol exists for this species in the hobby, and success has been anecdotal. Aquarists who have attempted breeding generally recommend a large, mature brackish system, excellent water quality, live foods to condition breeders and patience with spawning triggers that may be tied to water condition changes or seasonal cues that are difficult to replicate in captivity.
In the aquarium
The figure-eight puffer is considered one of the more tractable puffers for the experienced aquarist, though it is emphatically not a community fish by most standards. Its relatively modest adult size (around 3 in) suits tanks in the range of 15 US gal or more, with strong filtration — puffers are heavy-waste producers and sensitive to deteriorating water quality, particularly elevated nitrite and nitrate. Frequent water changes and over-sized mechanical filtration are the norm.
The beak is a non-negotiable care point: it never stops growing and must be worn down by regular exposure to hard-shelled prey. A diet primarily composed of live or frozen snails, small crustaceans and shellfish is essential; soft foods alone will lead to beak overgrowth that requires manual trimming by an experienced handler — a stressful and invasive procedure. Like all puffers, this species is scaleless and lacks true gill covers, making it sensitive to medications; copper-based treatments are toxic to puffers and must never be used. Dose any medication conservatively and carefully.
The figure-eight is generally reported as somewhat less aggressive than the green spotted puffer and may tolerate robust brackish companions such as mollies or bumblebee gobies in a sufficiently large tank, though individual temperament varies and fin-nipping can occur — any pairing should be monitored closely. Puffers should never be lifted out of water into air; if they inflate they do so with water, and draining an inflated puffer is stressful. Tetrodotoxin is present in the skin and organs, so handling should be minimised and done with care; the fish are not dangerous to keep but should not be eaten and hands should be washed after contact.
The water must be brackish — a specific gravity of SG 1.005–1.008 is the recommended range, warm (72–82 °F), hard and alkaline, reflecting the estuarine environment. Unlike the green spotted puffer, the figure-eight does not require a progression toward near-marine salinity as it matures, which makes long-term maintenance somewhat simpler.
Conservation
Dichotomyctere ocellatus is listed as Data Deficient (DD) on the IUCN Red List, assessed in 2019. The DD listing reflects a genuine absence of population data rather than a conclusion about its conservation status: the species is known from coastal localities across Southeast Asia but robust survey data on abundance, population trends or threats is lacking. It is not listed on CITES Appendices.
The habitats it occupies — estuaries, mangrove margins and tidal rivers along the Sunda coastline — are among the most heavily impacted coastal ecosystems in the world. Mangrove clearance for aquaculture and coastal development, pollution from agricultural runoff and urbanisation, and the disruption of tidal river hydrology by upstream dams and water extraction are the dominant pressures across its range. The figure-eight is collected for the ornamental fish trade, but at what scale and with what effect on wild populations is unknown. Until baseline survey work is conducted across the Mekong delta, Peninsular Malaysia and Borneo coastlines, its status will remain genuinely uncertain.