Taxonomy & naming
Chitala lopis was described by the Dutch ichthyologist Pieter Bleeker in 1851, with a type locality at Jakarta (then Batavia), Java. As with several congeners, the parenthetical authority — (Bleeker, 1851) — signals that Bleeker's original description placed the species in a different genus; it has since been reclassified into Chitala, the genus of Old World featherback knifefishes within the family Notopteridae. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) lists Chitala lopis as a valid name within Notopteridae, which in turn sits inside Osteoglossiformes, the bonytongue order — a scattered, deep-time radiation found on four continents (South America, Africa, Southeast Asia and Australasia) that also includes the arowanas, arapaima, African butterflyfish and the electric mormyrids.
The genus name Chitala derives from a South Asian vernacular name (chital/chitol) long used for river knifefishes; the species epithet lopis is of less certain derivation, likely adapted by Bleeker from a local Javanese or Sundanese name for the fish, though the precise origin is not well documented in the sources consulted here. Chitala lopis is the largest species in its genus, plainer-flanked than the smaller, ocellated Chitala ornata (the clown knifefish) and distinct from other Sundaland and mainland relatives such as Chitala borneensis, Chitala blanci and Chitala hypselonotus — a complex of large, similar-looking featherbacks that older literature sometimes lumped together under the name "lopis" before taxonomic revision separated them. It is worth stressing, as with every Chitala, that this is a Notopterid, not a Gymnotiform: the resemblance to South American "knifefishes" such as the black ghost knife is purely convergent, two unrelated lineages arriving independently at the same blade-bodied, undulating-fin swimming style.
Morphology
The giant featherback has the classic featherback build, taken to its largest extreme: a deep, strongly laterally compressed, blade-shaped body tapering to a point at the tail, a small head with a large, upturned mouth, and a long ribbon-like anal fin running from behind the belly almost to the tail, where it merges with a reduced caudal fin. The dorsal fin is tiny and set far back, and the pelvic fins are minimal, so nearly all propulsion comes from an undulating wave passed along the anal fin — the slow, hovering, back-and-forth swimming style shared across the genus, which lets the fish hold position or reverse instantly while hunting. The body carries small cycloid scales and a silvery-grey to olive ground colour, generally plainer and less strongly marked than the bold, pale-ringed ocelli of the smaller clown knifefish.
Size estimates vary by source but agree this is the largest member of the family Notopteridae: Seriously Fish and FishBase both cite a maximum around 39.4–59.1 in total length, while other hobby sources give a more conservative 37.4–39.4 in as typical for large specimens. Like other Notopterids it is an obligate air-breather, drawing oxygen at the surface through a vascularised, lung-like swim bladder, an adaptation that lets it tolerate the low-oxygen forested tributaries and floodplain waters it inhabits.
Habitat
As usually reported, Chitala lopis ranges across mainland and island Southeast Asia: the Mekong basin (Laos, Cambodia, Thailand), the separate Chao Phraya and Mae Klong basins of Thailand, Peninsular Malaysia, and the Sundaland islands of Sumatra, Borneo and Java (Indonesia), with the type locality at Jakarta, Java. It is a freshwater specialist, occupying the lower reaches of main river channels and forested tributaries with rocky or woody substrate rather than open, featureless water.
Cited water conditions are warm and tropical: Seriously Fish gives a temperature range of roughly 72–82 °F and a pH of about 6.0–8.0, while a narrower 73–81 °F and pH 6.2–7.2 is quoted elsewhere for aquarium keeping. Either way, this is soft-to-moderately-hard, slightly acidic to neutral river water, not the mineral-rich alkaline water of the African rift lakes.
Feeding
The giant featherback is a nocturnal ambush predator. By day it shelters among rock and woody cover, emerging after dark to hunt small fish, prawns and other crustaceans, and earthworms, using the same undulating anal-fin swim as its relatives to stalk and strike with precision in low light. Its obligate air-breathing habit — drawing oxygen from the surface via a vascularised swim bladder — is part of the same nocturnal, floodplain-adapted lifestyle, letting it exploit warm, still, sometimes oxygen-poor tributary water that would exclude a gill-only predator of similar size.
In captivity it takes to frozen and prepared carnivore foods once settled, but at its adult scale almost nothing shares a tank safely: any fish small enough to be engulfed is at risk, and given the species' size that includes many fish an aquarist would not normally think of as "small".
Mating
Wild breeding is reported to coincide with the rainy season, consistent with the flood-pulse spawning pattern documented across river-dwelling Notopterids, including the better-studied clown knifefish. Chitala lopis is a substrate spawner rather than a mouthbrooder or open scatterer: adhesive eggs are laid onto hard submerged surfaces such as wood, roots or rock rather than released into open water.
Courtship and pairing behaviour specific to this species are not well documented in the sources consulted here — data sparse. Its far larger adult size and much lower profile in the aquarium trade than Chitala ornata mean the field and captive breeding record for Chitala lopis is thin by comparison.
Breeding
No confirmed captive breeding of Chitala lopis in the aquarium hobby has been documented — hobby sources describe the species as a substrate spawner in the wild without a reliable home-aquarium spawning record. If parental care follows the pattern established for the genus, as in the smaller Chitala ornata, the male would guard and fan the eggs on their nest site until they hatch, but this has not been specifically confirmed for Chitala lopis.
Given its scale, its recent Extinct assessment, and the general absence of a captive-breeding record, essentially all giant featherbacks reaching aquarists are presumed to be wild-collected rather than tank-raised, which sits uneasily alongside the species' conservation status (see "Conservation").
In the aquarium
Where it is available at all, Chitala lopis is a classic size trap and the largest species in its family: reported to reach 39.4–59.1 in total length, against a much smaller trade size, with a lifespan cited at around 50 years — a multi-decade commitment. A tank on the order of 2,0 US gal or more is the minimum figure quoted for a full-grown adult, and a secure, tight-fitting lid is not optional — the species is noted as an exceptional jumper. As with the rest of its genus it is a nocturnal ambush predator that spends daylight tucked against rock or wood cover, so dim lighting and robust, too-large-to-swallow tankmates suit it far better than a bright community display, and as an obligate air-breather it needs unobstructed, regular access to the surface.
Given the species' Extinct IUCN assessment and its only recently reported rediscovery in Java, genuine wild-collected Chitala lopis should not be assumed to be in general circulation, and stock historically sold in the trade under this name may in fact belong to closely related, formerly conflated Sundaland species such as Chitala borneensis, Chitala blanci or Chitala hypselonotus. Anyone offered a fish under this name should treat the identification with some scepticism, and in any case should expect to be taking on one of the largest and longest-lived featherbacks in the hobby — housing on a public-aquarium scale is the honest endpoint for a fish grown to full adult size.
Conservation
The IUCN Red List assessed Chitala lopis as Extinct, an assessment dated to 2019 — a striking status for a fish usually mapped across a wide swathe of mainland and island Southeast Asia. The assessment reflected the absence of any confirmed record from the species' Javan type locality since Bleeker described it from Jakarta in 1851, until 2023, when Indonesian researchers reportedly rediscovered the giant featherback at that same type locality. The IUCN's formal reassessment has not yet caught up with the discovery, so the Extinct listing remains the fish's official status pending review, even though a wild population is now known to survive.
The broader distribution data compiled by aggregators such as FishBase and GBIF — spanning the Mekong, Chao Phraya and Mae Klong basins, Peninsular Malaysia, Sumatra and Borneo as well as Java — is a reminder that "Chitala lopis" has historically been used loosely for a complex of large Sundaland and mainland featherbacks that taxonomic revision has since split into several separate species, including Chitala borneensis, Chitala blanci and Chitala hypselonotus. Whatever the eventual resolution of that complex, the reported rediscovery of a giant featherback at Bleeker's original Javan locality after more than 170 years without a confirmed sighting is a genuine conservation good-news story, and a reminder that "Extinct" assessments for large, wide-ranging, poorly surveyed tropical freshwater fish can be premature.