Taxonomy & naming
Characidium krenak was described in 2022 by Oliveira-Silva, Santos, Lopes and Zanata in Neotropical Ichthyology, based on a holotype (MZUSP 125896, 2.5 in SL) and a series of paratypes measuring roughly 1.5–2 in SL collected from the rio Piranga and rio Santo Antônio sub-basins of the upper Rio Doce, Minas Gerais, Brazil. It belongs to the family Crenuchidae — the South American darters — in the genus Characidium, one of the most species-rich genera of small benthic characins in the Neotropics, and a group that has absorbed a steady stream of new species descriptions from isolated river basins over the past two decades as taxonomists work through cryptic, morphologically similar populations.
The species epithet honours the Krenák people, an indigenous group whose traditional territory lies along the Rio Doce, the river system from which the type series was collected. As with many recently described Characidium, C. krenak is distinguished from its congeners by a combination of small, often subtle characters rather than one obvious diagnostic feature — a pattern typical of the genus and part of why so many of its species have been described only in the last few decades using detailed comparative material.
Morphology
The type description records a holotype of 2.5 in standard length with paratypes in the roughly 1.5–2 in SL range, putting Characidium krenak in the small-to-modest size class typical of the genus — a slender, elongate darter rather than a deep-bodied fish. Diagnostic features noted in the original description include the absence of scales between the isthmus and the cleithrum, a present adipose fin, two to four scale rows between the anus and the anal-fin origin, two rows of teeth on the dentary, a parietal branch present on the supraorbital canal, four scale rows above the lateral line, and the lack of conspicuous dark bands on the caudal fin — a set of characters used to separate it from superficially similar Characidium species in neighbouring drainages.
As in other Characidium, the body plan is built for a life spent perched on the substrate rather than swimming in the water column: a torpedo-shaped body, a flattened ventral profile, and paired fins used to prop the fish at rest on rock, sand or leaf litter between short, quick dashes. No specific colour-pattern description beyond the caudal-fin banding character is available from the cache for this species, and no photographs or live-colour notes were located, so further detail here would be guesswork rather than documented fact.
Habitat
Characidium krenak is known only from the upper Rio Doce basin in Minas Gerais, Brazil, specifically the rio Piranga and rio Santo Antônio sub-basins, at elevations of roughly 1969–2953 ft. The type series was taken from tributary streams described in the original description as ranging from clear to dark water, with flow varying from slow to turbulent and substrate composed of a mix of rock, sand and clay — typical conditions for the small, rocky headwater and mid-order streams that Characidium species favour throughout their range.
No water-chemistry measurements (temperature, pH or hardness) were captured for this specific species in the available sources, and it would be irresponsible to invent them; what can be said is that the upper Rio Doce sits in a subtropical-to-tropical highland part of south-eastern Brazil, and that Characidium darters in general are stream-bed specialists tied closely to flowing water with a firm substrate rather than to still, vegetated water.
Feeding
No stomach-content or diet study specific to Characidium krenak was located. Characidium as a genus are documented micro-predators: they perch on the bottom and dart out to take small aquatic invertebrates — insect larvae, tiny crustaceans and other micro-fauna — picked from the substrate or the water column immediately around them, and they are not generally reported taking plant material or large prey.
Genus-level aquarium accounts of Characidium note that these fish often will not reliably take flake food and do best on small live or frozen foods such as bloodworm, mosquito larvae, brine shrimp, daphnia and cyclops — a diet consistent with their role as small, opportunistic invertebrate hunters on the stream bed. There is no reason from the available evidence to expect C. krenak to differ from this genus-wide pattern, but no direct observation of this species feeding has been published.
Mating
No courtship or pairing behaviour has been documented for Characidium krenak specifically; the type description is a taxonomic account based on preserved specimens and does not report field observations of spawning behaviour. Sexual dimorphism was not described for this species in the sources reviewed, and it should not be assumed present or absent without evidence.
At the genus level, Characidium and their close relatives among the crenuchid darters are reported to spawn in response to environmental triggers such as a drop in temperature associated with a water change, with courtship involving close pairing near the substrate before eggs are released — but this is genus-level, largely aquarium-derived information, not a documented account of C. krenak itself, and should be read as background rather than as a claim about this species.
Breeding
There is no published breeding record for Characidium krenak — it has never, as far as the available sources show, been kept or bred in the aquarium, and it has no meaningful presence in the hobby. Extrapolating cautiously from genus-level accounts, Characidium darters as a group are typically described as substrate egg-scatterers: eggs are released over rock, sand or fine-leaved plants in soft, acidic water with no parental care, and eggs are reported to hatch in roughly 30–40 hours in aquarium settings for other Characidium species.
This is worth stating plainly rather than glossing over: nothing in the cache or in general taxonomic literature confirms that mode for C. krenak itself, only for congeners. Given how recently the species was described (2022) and its restriction to a specific set of Brazilian headwater streams, it should be treated as essentially unknown in cultivation, not as a species with an established breeding protocol.
In the aquarium
Characidium krenak is not an aquarium fish in any practical sense — it was described from a small number of preserved museum specimens and has no track record in the hobby, no trade name, and (based on the available sources) has not been exported or bred. Anything written here about tank size, tankmates or aquascaping for this specific species would be invented rather than documented, so none is offered.
What can be said honestly, drawing on the genus, is that Characidium darters in general are modest-sized, bottom-oriented fish suited to a well-oxygenated, current-swept aquarium with a hard substrate and open swimming lanes rather than dense, static planting — a setup that mimics the rocky, flowing streams the genus favours. Should live specimens of C. krenak ever reach the hobby, that genus-typical setup, plus small live or frozen invertebrate foods, would be the reasonable starting point, but this is inference from relatives, not a care record for the species itself.
Conservation
Characidium krenak has not been evaluated by the IUCN Red List; as a species described only in 2022, it currently carries no formal conservation status (Not Evaluated). It is known only from a restricted set of tributary streams in the upper Rio Doce basin in Minas Gerais, Brazil — a river system that has faced serious documented environmental pressure, most notably the catastrophic 2015 Fundão tailings dam collapse that sent a wave of mining waste down the Rio Doce, though the type locality streams for this species were not necessarily in the directly affected mainstem.
Given its narrow known range and the general vulnerability of small-range, recently described headwater fishes to habitat degradation, sedimentation and water-quality change, C. krenak is a reasonable candidate for future conservation concern even though no formal assessment yet exists. As with many newly described Characidium, the priority from a conservation standpoint is simply more survey work to establish how widely the species actually occurs and what pressures its specific streams face.