Taxonomy & naming
Hisonotus bocaiuva was formally described by Roxo, Silva, Oliveira and Zawadzki in 2013, in a revision of Hisonotus from the São Francisco basin published in Zootaxa. The holotype measures 1 in SL and was collected from the Córrego Cachoeira, a small tributary of the Jequitaí River in the upper São Francisco drainage, near the municipality of Bocaiúva in Minas Gerais state, Brazil. Paratypes span 0.5–1 in SL, confirming that the holotype is near maximum size.
The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hisonotus bocaiuva within the genus Hisonotus Eigenmann & Eigenmann, 1889, which belongs to subfamily Hypoptopomatinae — one of the five major subfamilial groupings within Loricariidae. Hypoptopomatinae contains numerous small, largely benthic algae-scrapers distributed across the Neotropics, with notable diversity in Atlantic coastal drainages and the major interior basins of Brazil.
H. bocaiuva is distinguished from its congener H. devidei — the other São Francisco Hisonotus described in the same paper — by having the abdomen partially or completely covered by dermal plates, and by lacking the prominent, contrasting dark geometric spots on the anterodorsal body region that characterise H. devidei. Both species share conspicuous dark blotches of distinct shapes irregularly dispersed over the lateral and dorsal surfaces, and are known only from the São Francisco basin.
Morphology
Adults reach approximately 1 in standard length — an exceptionally small maximum size even among the Hypoptopomatinae, which tend toward compact body plans. Like all Hisonotus, the body is encased in the overlapping bony scutes characteristic of Loricariidae, providing armour over the flanks and dorsum. The abdomen of H. bocaiuva is partially or completely covered by dermal plates, a trait shared with some but not all congeners and used diagnostically within the genus.
Ground colouration is pale to mid-brown with conspicuous dark blotches of distinct shapes irregularly dispersed over the lateral and dorsal surfaces. This patterning is common to H. bocaiuva and H. devidei, but in H. bocaiuva the anterodorsal region lacks the bold, high-contrast geometric spots that make H. devidei more visually striking at close range.
The ventral surface is largely pale. The mouth is positioned ventrally with the lip modified into an adhesive disc — the characteristic loricariid arrangement that allows the fish to cling to substrate against current. Detailed odontology and fin-ray counts are documented in the original description by Roxo et al. (2013). No sexual dimorphism data are available for this species in the published literature.
Habitat
The type locality is the Córrego Cachoeira, a small stream draining toward the Jequitaí River within the upper São Francisco basin, Bocaiúva municipality, Minas Gerais. This region sits at the ecological boundary between Cerrado savanna and Caatinga dry scrubland — a transition zone characterised by streams with marginal vegetation, seasonal flow variation, and substrates ranging from sand to rock.
Small Cerrado and Caatinga streams of this kind typically carry warm, relatively clear water, though seasonal floods can temporarily increase turbidity and conductivity. Marginal gallery forest provides leaf litter, submerged wood, and shading to the stream channel. No precise physical-chemical field data (temperature, pH, conductivity) have been published for the Córrego Cachoeira itself, and H. bocaiuva is known only from this single drainage system based on published records.
Feeding
No specific feeding studies have been published for Hisonotus bocaiuva. Based on loricariid subfamily affinity and general Hisonotus biology, the species is presumed to feed as an aufwuchs and algae micro-grazer — using its suctorial disc mouth to rasp biofilm, diatoms, filamentous algae, and fine organic detritus from rock, wood, and leaf surfaces. This micro-grazing mode is typical of Hypoptopomatinae as a group.
At 1 in maximum size, the foraging footprint of this species is extremely small. In the wild it likely exploits fine-scale patches of biofilm on stable substrates — cobbles, submerged roots, and leaf litter — in areas of low to moderate current where aufwuchs can establish. The combination of small size and Cerrado stream habitat suggests a specialist of benthic microhabitats rather than open water foraging.
Mating
No courtship or mating behaviour has been described for Hisonotus bocaiuva in the scientific literature. Among Hypoptopomatinae more broadly, reproductive behaviour varies but commonly involves spawning on hard substrates such as rock faces, leaf litter, or submerged wood, with adhesive eggs deposited in sheltered locations. Whether H. bocaiuva follows this pattern is unknown.
Given its extremely small body size — one of the smallest adult sizes within Loricariidae — the species likely matures rapidly relative to larger loricariids and may have a short life cycle tied to the seasonal hydrology of Cerrado streams. No data on sex ratio, territorial behaviour, or mating seasonality are available in the published record.
Breeding
No breeding data exist for Hisonotus bocaiuva in the literature, and the species is not known to have been bred in captivity. Given the highly restricted range and the small number of specimens examined in the original description, it has not attracted the attention of specialist catfish keepers to date.
For context, related Hypoptopomatinae such as Otocinclus spp. and some Parotocinclus are known to deposit adhesive eggs on plant leaves or smooth hard surfaces, with little or no parental care. Whether H. bocaiuva shares this reproductive strategy must remain speculative until field or captive observations are published.
In the aquarium
Hisonotus bocaiuva is not available in the ornamental fish trade and is not kept in home aquaria. Its extremely small size (under 1 in SL), restricted range, and very limited commercial collection mean it is known only to specialist ichthyologists and is absent from fishkeeping literature.
For completeness: any loricariid of this size and subfamily affiliation would require a mature, well-filtered small aquarium with a biofilm-rich environment — smooth stones, fine sand substrate, and moderate to gentle current — rather than heavy water movement. Water chemistry should reflect the Cerrado interior origin: warm tropical temperatures, soft to moderately hard water. No practical husbandry data are available, and acquisition of wild specimens would require scientific collecting permits in Brazil.
Conservation
Hisonotus bocaiuva was assessed by the IUCN Red List as Least Concern in November 2018. At the time of assessment, no major threats had been identified, and the species was considered viable within its known range in the Jequitaí drainage.
Nonetheless, the species is known from a single small-stream drainage system — the Córrego Cachoeira — and any significant degradation of that watercourse would place the population at immediate risk. Cerrado and Caatinga transition-zone streams in Minas Gerais are subject to ongoing pressures including agricultural water extraction, sedimentation from deforestation, and disruption of riparian gallery forest. The intrinsically small range of H. bocaiuva means that threats operating even at a local scale could have population-level consequences. Monitoring of the Jequitaí drainage and verification of whether the species occurs in additional nearby streams would be valuable future work.