Taxonomy & naming
Hisonotus chromodontus was formally described by Britski and Garavello in 2007 in the Brazilian Journal of Biology (67(3):413–420), based on specimens collected in creek headwaters of the upper Rio Tapajós drainage, Mato Grosso state, Brazil. The Catalog of Fishes (Eschmeyer, CAS; species ID 69959) recognises the valid combination Hisonotus chromodontus Britski & Garavello, 2007.
The species belongs to the subfamily Hypoptopomatinae, the group of small, plated catfishes colloquially called 'otocinclus relatives' or micro-plecos, distinguished from the larger Loricariidae by their diminutive size, complete bony armour on the abdomen in adults, and benthic aufwuchs-grazing habits.
Note on nomenclature: ETYFish (Scharpf & Lazara, 2026) lists this species as Rhinotocinclus chromodontus, reflecting a proposed genus-level reclassification by Roxo et al. (2020) that reorganises part of the traditional Hisonotus into the resurrected genus Rhinotocinclus. That realignment has not been adopted by FishBase or the Catalog of Fishes as of the date of this article; we follow CoF as the site's taxonomic authority and retain the current valid name Hisonotus chromodontus. Users researching this species should be aware that literature published after 2020 may use either name.
Morphology
Adults reach approximately 1.5 in standard length (SL). The body is elongated and fully armoured, with 23–24 plates in the longitudinal series. In adults of about 1 in SL and above, the abdomen is entirely covered with large bony plates — a character useful in separating it from congeners in which abdominal coverage is partial or absent.
The diagnostic feature of the species is the reddish-brown tip of the teeth, present on both the premaxillary (20–40 teeth) and the dentary (15–38 teeth) — the character directly referenced by the species epithet. The lateral line is almost complete, with 19–22 perforated plates and one or two non-perforated plates. The dorsal surface of the pectoral spine bears approximately five longitudinal series of odontodes.
Coloration is dominated by a large dark-brown lateral stripe running from the tip of the snout through the lower orbit to the end of the caudal peduncle. Transverse dark bars are very inconspicuous or absent, producing a relatively plain pattern compared to some congeners. Trophic level is estimated at 2.4 based on data from related species.
Habitat
The species is known from the headwaters of the Rio Tapajós drainage in Mato Grosso state, Brazil. The type locality lies in flat, shallow creek habitat on the headwaters of this system, characterised by clear water, low current, and sandy substrate. Field notes from the original description record that the holotype was collected in a creek severely altered by human activities — a location alongside a trail with very shallow water, banks deprived of vegetation, and a swampy area on the opposite bank supporting mainly Typha and Gramineae.
Like others in the genus, H. chromodontus is a freshwater, demersal, and presumably subtropical to tropical species. No published pH or temperature data are available for the specific collection sites; water chemistry parameters for this species must be inferred from the general Tapajós basin literature and from ecology data on congeners. Hisonotus species generally favour clear, well-oxygenated, soft to moderately hard water.
Feeding
Hisonotus chromodontus is a micro-grazer. Based on its mouth morphology, dentition, and the feeding ecology of its subfamily, it grazes aufwuchs — the thin biofilm of algae, diatoms, bacteria, and fine detritus that coats submerged surfaces in its native streams. The trophic level of 2.4 (estimated from relatives) is consistent with herbivorous to omnivorous grazing on benthic biofilm rather than predation on invertebrates.
No specific dietary observations exist for this species from captivity, as it is not established in the aquarium hobby. By analogy with other Hypoptopomatinae such as Otocinclus and related Hisonotus, the diet is expected to consist primarily of algal biofilm, with soft algae, diatoms, and fine organic matter making up the bulk of intake.
Mating
No observations of mating behaviour have been published for Hisonotus chromodontus. The species is not held in aquaria in any documented capacity. General loricariid reproductive biology suggests that males of Hypoptopomatinae defend territories or spawning sites and display secondary sexual characters — such as elongated or differently textured odontodes — during the breeding season, but no specific data exist for this taxon.
Breeding
No breeding data are available for Hisonotus chromodontus. The species has not been bred in captivity, and published accounts of reproduction are absent from the literature. Members of Hypoptopomatinae generally lay adhesive eggs on hard substrate, with varying degrees of parental care depending on genus; whether H. chromodontus follows this pattern is not established.
In the aquarium
Hisonotus chromodontus is not present in the ornamental fish trade and has not been maintained in aquaria in any documented capacity. Husbandry notes must therefore remain speculative and grounded in what is known about the subfamily broadly.
At 1.5 in SL it is among the smallest loricariids described. Any aquarium attempt would call for a small, quiet tank with clean, well-oxygenated water, abundant surfaces for biofilm growth, and an absence of aggressive tankmates. Water parameters consistent with soft, slightly acidic to neutral conditions typical of clear-water streams in central Brazil would be appropriate starting points. Given its rarity and micro-habitat specificity, this species is unlikely to enter the hobby in the foreseeable future.
Conservation
The IUCN Red List assessed Hisonotus chromodontus as Least Concern in November 2018, based on its presence in the upper Rio Tapajós drainage. The assessment acknowledges that the species is known from relatively few localities. The original collection site was described as severely degraded by human land-use activities at the time of collection, and the broader Tapajós headwaters region in Mato Grosso faces ongoing pressures from agricultural expansion and associated sedimentation and deforestation. The Least Concern status reflects the absence of documented population decline rather than evidence that the species is widespread or abundant.