Taxonomy & naming
Bunocephalus hertzi was formally described in 2020 by Esguícero, Castro and Pereira in the journal Zootaxa, based on specimens from the upper Rio Paraná basin in Brazil. It belongs to the family Aspredinidae, the banjo catfishes, within the genus Bunocephalus, a group of small, flattened, substrate-dwelling South American catfishes. The Catalog of Fishes treats Bunocephalus hertzi as a valid, currently accepted name.
The species was distinguished from its closest relatives — including a redescribed Bunocephalus larai (Ihering, 1930) from the same paper — by a longer coracoid process (part of the pectoral girdle) and by a distinctive pattern of skull ornamentation, with five bony protuberances on the head. As with many recently split South American catfishes, older regional records from the upper Paraná may have been lumped under other Bunocephalus names before this species was recognised as distinct; specimens should be referred to current taxonomic literature rather than older, broader identifications.
Morphology
Like other banjo catfishes, Bunocephalus hertzi has an unmistakable flattened, teardrop-shaped body: a broad, depressed head and forebody tapering to a slender tail, an outline that gives the family its common name. The skin is naked — Bunocephalus and its relatives have no scales, but instead a leathery, often mottled sandy-brown to grey skin that camouflages the fish against riverbed sediment and leaf litter.
The species is small even by banjo catfish standards. The holotype measured 2 in standard length (about 2 in SL), with a paratype at 2 in SL, so this is a genuinely diminutive fish that never approaches the size of some other Aspredinidae. It carries the stout, serrated pectoral spines typical of the family, which can be locked into an erect defensive position — a feature to respect when handling the fish (see "In the aquarium").
Habitat
Bunocephalus hertzi is known only from tributaries of the upper Rio Paraná basin in Brazil, including the Pardo, Paranapanema, Paranaíba and Ivinhema drainages. The type locality is the main channel of the Mogi-Guaçu River, a relatively large river roughly 279 ft wide and 7 ft deep at the collection site, with turbid water, a sandy bottom, marginal sandbanks and beds of floating macrophytes. Specimens were collected among plant debris and leaf litter along the river margins during the dry season.
Water here is warm subtropical river water: reported values for the genus in this region put temperature around 75–82 °F and pH roughly 6.0–7.0, soft to moderately hard. As a bottom-dweller in a turbid, sediment-rich river, it relies on camouflage against sand and detritus rather than open swimming, and is rarely seen in the water column.
Feeding
Banjo catfishes in general are nocturnal benthic omnivores, and Bunocephalus hertzi fits that pattern: reports from its description note it hiding in leaf litter or buried in substrate by day, consistent with a fish that forages after dark for small invertebrates and detritus on and in the riverbed.
In the aquarium, congeners such as Bunocephalus coracoideus are kept on sinking pellets, frozen foods and other prepared foods offered after lights-out, since a nocturnal bottom-feeder is easily out-competed by more active daytime fish. The same approach is the sensible default for B. hertzi in the absence of species-specific feeding data.
Mating
Species-specific mating behaviour for Bunocephalus hertzi has not been documented; it is a recently described species known mainly from its type series, and detailed reproductive biology has not been published. Breeding accounts for the genus Bunocephalus, based on better-studied congeners, describe eggs being scattered in groups over sandy substrate rather than carried by the female — unlike some other genera in the family Aspredinidae (such as Platystacus and Aspredo), where females carry fertilised eggs attached to the belly skin via fleshy stalks called cotylephores. Bunocephalus does not use that egg-carrying strategy.
Breeding
There are no published aquarium or field breeding records for Bunocephalus hertzi specifically. Based on the genus Bunocephalus generally, spawning is understood to involve the female scattering a relatively large clutch — reported in the low thousands of eggs for related Bunocephalus — over sandy substrate, with no parental care of the type seen in some other Aspredinidae. Given how recently this species was described (2020) and how little is known even of its basic ecology beyond the type locality, it should be considered essentially unbred and unknown in captivity; any account claiming otherwise should be treated with caution.
In the aquarium
Bunocephalus hertzi is not established in the aquarium trade and there is no evidence it is currently kept or bred by hobbyists; this account is offered as a guide should the species ever become available, drawing on its known biology and that of its congeners. At roughly 2 in SL it stays genuinely small, but it should still be given a soft sand substrate to bury into, leaf litter or plant debris for cover, and subdued lighting, since it is a nocturnal fish that spends the day hidden.
Two care points follow directly from its biology as a banjo catfish. First, it is scaleless, so like loaches, puffers and other naked-skinned catfishes it is more sensitive than scaled fish to copper and many medications — dose conservatively, often at half strength, and monitor closely. Second, it carries stiff, serrated, locking pectoral spines that can snag in a net and jab the handler; move it in a container rather than netting it. Feed sinking foods after lights-out so it is not out-competed by more active tankmates, and keep water on the warm, softer side reflecting its subtropical Paraná basin origin.
Conservation
Bunocephalus hertzi has not been formally assessed by the IUCN Red List; as a species described only in 2020, it is Not Evaluated. It is known only from the upper Rio Paraná basin in Brazil, a large river system that has been heavily modified by damming, agriculture and urbanisation, though the specific pressures on this species' populations have not been studied.
With no dedicated assessment and a distribution defined mainly by its type locality and a handful of nearby drainages, its conservation status should be treated as genuinely unknown rather than assumed safe. There is no indication it is currently part of the aquarium trade, so collection pressure is not a known concern for this species.