Taxonomy & naming
Hypostomus delimai was formally described by Zawadzki, de Oliveira and Debona in 2013. The holotype (INPA 6191, 9.5 in SL) was collected at Itupiranga, on the rio Tocantins, Pará, Brazil (5°07'29.6"S, 49°18'44.4"W). The species is recognised as valid in the Catalog of Fishes (Eschmeyer, CAS), with no synonyms listed; subsequent publications by Zawadzki et al. (2017) and Soares et al. (2021) have confirmed its standing.
The species belongs to the large and taxonomically complex genus Hypostomus Lacépède, 1803, which contains well over 150 described species across South and Central America. Within Hypostomus, members of the family Loricariidae are grouped under the subfamily Hypostominae. Diagnosis of H. delimai within its genus rests primarily on the pale spots on body and fins set against a darker ground colour, and a predorsal plate count of five to eight (mode seven) — a count that, in combination, distinguishes it from overlapping congeners in the Tocantins system.
Morphology
Adults reach up to 10 in standard length (SL), placing H. delimai among the larger representatives of Hypostomus. Like all loricariids, the body is encased in overlapping bony plates (scutes) arranged in longitudinal rows. Ground colour is darker, overlaid with a pale-spot pattern that extends across both body and fins — a character that features in the species' formal diagnosis.
The predorsal plate series counts five to eight plates, with seven being the modal count, which provides a useful diagnostic character alongside coloration. The head is broad and depressed, the mouth suctorial and ventral, and the lips bear numerous small papillae suited to rasping substrate surfaces. The caudal fin is forked, as is typical for the genus. No published data describe sexual dimorphism in detail for this species, though in Hypostomus generally, breeding males may develop odontodes on the snout and pectoral spines.
Habitat
Hypostomus delimai is known from the middle and lower Tocantins-Araguaia basin in Brazil. The type locality on the rio Tocantins near Itupiranga, Pará, is a large, turbid Amazonian river with rocky and sandy substrate. The species is described as inhabiting turbid water with mixed rocky and sandy substrate, occupying demersal (bottom-associated) positions.
Like many Hypostomus species, H. delimai is a facultative air-breather — capable of surfacing to gulp atmospheric oxygen when dissolved oxygen levels drop, an adaptation of considerable value in tropical floodplain systems where seasonally low oxygen can occur. No detailed water parameter data (temperature, pH, hardness) have been published for the type locality or other collection sites.
Feeding
Diet has not been specifically described for H. delimai in the published literature. Based on the general biology of Hypostomus, the species is expected to be an omnivorous grazer, rasping aufwuchs (algae, biofilm, diatoms, and fine detritus) from rocky and woody surfaces. Many medium-to-large Hypostomus also ingest sand and organic sediment while foraging. Some species in the genus supplement this diet with higher proportions of organic detritus or, in wood-rich habitats, wood pulp.
In the aquarium, related Hypostomus are typically maintained on algae wafers, spirulina-based foods, blanched vegetables (courgette, cucumber, sweet potato), and sinking catfish pellets, with driftwood available for rasping. Until diet studies are conducted for H. delimai specifically, this general Hypostomus feeding model is the most reasonable guide.
Mating
Reproductive behaviour has not been described in the literature for H. delimai. Within Hypostomus broadly, courtship typically involves males guarding suitable burrow or cavity sites, with females being attracted to conditioned males at these sites. Male Hypostomus commonly develop more pronounced odontodes on the pectoral spines and snout during the breeding season, and territorial competition between males can be intense where suitable nesting sites are limiting.
Given the species' medium-to-large adult size and its turbid-water habitat in a large river system, spawning in the wild likely takes place in burrows excavated in clay or muddy banks — a pattern well documented in similarly sized Hypostomus from other South American drainages — though this has not been verified for H. delimai.
Breeding
No breeding records for Hypostomus delimai in captivity have been located in the available literature. In the genus Hypostomus, reproduction follows a cave-spawning strategy: eggs are deposited in a sheltered cavity, and the male typically provides paternal guarding through the incubation period. Clutch sizes in medium-to-large Hypostomus can range from dozens to several hundred eggs depending on the female's size and condition.
Given its adult size of over 10 in SL, captive breeding of H. delimai would require a large aquarium with substantial cave structures. Until dedicated captive observations are published, the biology described here reflects genus-level patterns rather than species-specific data.
In the aquarium
Hypostomus delimai is not established in the ornamental fish trade and is essentially unknown in aquaria. Its maximum size of over 10 in SL means that any individual eventually kept would require a large, well-filtered aquarium — a minimum of 80 US gal for a single adult is a reasonable expectation by analogy with similarly sized Hypostomus.
Water should be tropical (the species is from equatorial Brazil), with robust mechanical and biological filtration to handle the significant waste production typical of large suckermouth catfish. Driftwood and rocky décor reflecting the rocky and sandy substrate of the Tocantins habitat would be appropriate. As a turbid-water fish, strong lighting and clear, open water are not prerequisites; subdued conditions with shelter are preferable.
For hobbyists who do encounter this species, general large-Hypostomus husbandry applies: a varied diet of algae wafers, sinking pellets, and blanched vegetables; regular substantial water changes; and compatible, non-aggressive tankmates of appropriate size.
Conservation
The IUCN Red List assessed Hypostomus delimai as Least Concern in November 2018. Its range covers the middle Tocantins-Araguaia basin in Brazil, and no major threats to the overall population were identified at the time of assessment. The population trend was recorded as stable.
Nonetheless, the Tocantins basin has been significantly altered by hydroelectric development — most notably the Tucuruí Dam, one of the largest hydroelectric plants in the world, which has reshaped large stretches of the river and affected fish communities in the middle and lower basin. The long-term implications for bottom-associated species such as H. delimai, which depend on specific substrate types, warrant continued monitoring even where immediate threat levels appear low.