Taxonomy & naming
Pao leiurus was described by Pieter Bleeker in 1850, originally under the genus Tetraodon, a name once applied broadly to freshwater and brackish puffers across Africa and Asia. Subsequent revisions have since restricted Tetraodon to the African species; the Asian mainland river puffers have been moved to the genus Pao, erected by Roberts in 1998. The Catalog of Fishes (Eschmeyer, CAS) records the current valid combination as Pao leiurus (Bleeker, 1850), with the parenthetical authority indicating the original placement in Tetraodon.
The genus Pao accommodates a cluster of freshwater puffers centred on the large river systems of Southeast Asia — the Mekong, the Chao Phraya and their tributaries — and encompasses some of the most studied ornamental puffers in the hobby, including P. suvattii (the Mbu-mimic "Arrowhead" puffer) and P. baileyi. GBIF records Pao leiurus as a valid accepted species (taxon key 8365527).
Morphology
Pao leiurus is a moderately built pufferfish reaching approximately 6.5 in standard length (SL) according to FishBase data, placing it in the mid-size range for the genus. The body is the classic tetraodontid shape: stocky and rounded in cross-section, tapering to a narrow caudal peduncle, with no true scales and no bony gill covers. The skin is rough and can carry small spinules depending on the fish's state of arousal.
Coloration is described as dirty brown or grey across the dorsum, with dusky, mottled patterning on the flanks and underside. The fish is marked with ocellated spots that show iridescent red, green, and blue reflections — a feature that distinguishes it within the genus and contributes to the trade name "target puffer" applied to certain spotted puffer species. The four fused teeth form a prominent beak visible from the front, a structure that never stops growing throughout the animal's life.
Habitat
Pao leiurus is a freshwater fish native to the Mekong basin, with its range extending across Thailand and into the broader mainland Southeast Asian river systems including those draining toward the Indonesian archipelago. FishBase records its distribution across the Mekong basin from Thailand to Indonesia. It inhabits the middle and lower reaches of large rivers and associated floodplain waters, typically in warm, near-neutral conditions.
FishBase water parameters for the species give a temperature range of approximately 75–82 °F in the wild, with aquarium hobby sources extending the keeping range down to around 72 °F. pH runs from approximately 7.0 to 7.5 and hardness from 8–12 dH, reflecting the moderately hard, near-neutral water characteristic of lowland Mekong-region rivers. Despite the "brackish puffer" trade name, Pao leiurus is primarily a freshwater species; any brackish tolerance is incidental and the species does not require saline conditions.
Feeding
Like all pufferfish, Pao leiurus is a predatory molluscivore in the wild, targeting hard-shelled invertebrates — snails, small crustaceans and shelled aquatic prey — which it crushes with its fused beak. The beak grows continuously throughout life and must be worn down by regular access to appropriately hard food; without this abrasion, the teeth can overgrow to the point of preventing normal feeding, requiring veterinary trimming.
In the aquarium, a varied diet of live or frozen snails, shrimp, shellfish and hard-shelled crayfish tails provides both nutrition and the mechanical wear the beak requires. Soft foods such as earthworms and bloodworm can supplement the diet but should not replace hard-shelled items. The fish is an active, assertive feeder.
Mating
Detailed mating observations for Pao leiurus specifically are not well documented in the published or community literature. What is known from congeners such as P. suvattii and P. baileyi suggests that Pao species are substrate spawners in which the male plays a role in tending eggs after deposition; however, a confirmed description of courtship behaviour in P. leiurus has not appeared in available sources.
The species is known to be oviparous (egg-laying). In the genus more broadly, males are typically smaller and slimmer than gravid females, and pairing in captivity often requires careful management given the aggressive, solitary disposition of the fish.
Breeding
Breeding in Pao leiurus has not been well documented in the aquarium hobby or scientific literature. Community sources note that it is oviparous and that breeding details are data sparse. By analogy with the better-known congeners P. suvattii and P. baileyi — in which males guard eggs laid on a flat substrate — Pao species are understood to be substrate spawners with paternal egg-guarding, but this has not been confirmed for P. leiurus in published accounts.
Anyone attempting to breed this species should be prepared for the substantial aggression typical of the genus: the two fish must be monitored closely during any introduction, with refugia available, and separated if the female shows signs of severe stress or injury. Induced conditioning through live food and simulating seasonal water-parameter cycles (temperature drop followed by warming, water changes) has been used with some congeners.
In the aquarium
Pao leiurus is an advanced-level fish that demands a dedicated setup and an experienced keeper. It is highly aggressive and territorial and must be kept alone or in a species-only aquarium — it will bite fins, eyes and flesh from any tankmate, and even conspecifics require careful management. A minimum aquarium of around 30 US gal (approximately 30 US gallons) is the floor suggested in community sources, with ample shelter through rockwork and robust plant cover.
The beak is the single most critical husbandry point: snails, small shellfish and hard-shelled crustaceans must be offered regularly — not as a treat but as a dietary staple — or the fused teeth will overgrow. Puffers are messy, high-waste feeders and the aquarium requires powerful biological filtration and frequent, substantial water changes to maintain water quality. Parameters should be kept warm (72–82 °F), near-neutral (pH 7.0–7.5) and moderately hard, matching the Mekong lowland origin of the species.
Puffers lack true scales and have no bony operculum; they are highly sensitive to medications. Copper-based treatments must never be used, and other medications should be dosed at reduced rates with careful observation. The fish's inflation reflex — it gulps water to expand the body as a defence — is stressful and potentially damaging to the swim bladder; fish should never be lifted out of water to trigger this response. Skin and organs carry tetrodotoxin and should not be handled without care.
Conservation
Pao leiurus is assessed as Least Concern (LC) on the IUCN Red List, reflecting a reasonably wide distribution across the Mekong basin and associated drainages of mainland Southeast Asia. The species does not appear to face acute trade pressure in the same category as some narrow-range endemics.
Nonetheless, the Mekong and its tributaries face severe anthropogenic pressures: a cascade of large hydroelectric dams on the main stem has altered hydrology, blocked fish migration corridors and disrupted seasonal flooding cycles that many riverine fishes depend on for breeding. Agricultural runoff, pollution and habitat conversion in the lowland floodplains further affect freshwater biodiversity. The long-term trajectory of Mekong river puffers, including P. leiurus, is tied to the broader fate of the basin's freshwater ecosystem.