Taxonomy & naming
Knodus savannensis was described by the French ichthyologist Jacques Géry in 1961. It is placed in Knodus Eigenmann, 1911, a genus of the family Characidae that contains numerous small, lightly built characins distributed across multiple river drainages in South America. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Knodus savannensis Géry, 1961.
The type locality has a degree of complexity noted by Lima & Géry (2001): two candidate sites in the Tocantins basin have been proposed — one near the municipality of Itacajá in Tocantins state, in the region between the Manoel Alves Pequeno and Vermelho rivers (approximately 8°19'S, 47°25'W), and another on the Javaés River at Bananal Island (approximately 11°S, 51°W). Further revisionary work on the genus is needed to fully resolve species boundaries and locality assignments within Knodus.
The specific epithet savannensis refers to the savanna (cerrado) landscape of the Tocantins interior where the type material was collected — one of the few Knodus names that directly evokes its biogeographic setting rather than honouring a collector or institution.
Morphology
Knodus savannensis reaches a maximum recorded total length of 2.5 in, placing it among the smaller members of its genus. Like other Knodus, it is a slender, fusiform characid with a relatively unspecialised body plan: a laterally compressed but not deep-bodied form, a terminal mouth, and the characteristic adipose fin of the Characiformes.
Detailed meristic and morphometric data for this species are sparse in the widely available literature. The genus Knodus as a whole tends toward a silvery or translucent ground colour with a dark lateral stripe or mid-lateral band of variable intensity, and a small humeral spot is present in several species. The precise colour pattern and diagnostic counts for K. savannensis are best established from the original description; field identifications in mixed-species assemblages can be difficult given the similarity among small Knodus.
Habitat
Knodus savannensis is known from the Tocantins River basin of Brazil. This drainage runs northward through the cerrado (savanna) and transitional zones of central Brazil before entering the lower Amazon system near the coast of Pará. The species is characterised by FishBase as benthopelagic and subtropical in affinity, reflecting the seasonally variable climate of the cerrado region, where temperatures can be cooler in the dry-season months than in classic Amazonian lowland habitats.
The cerrado streams and rivers that feed the upper Tocantins are typically clear to slightly turbid, with substrates of sand, gravel, or rock, and gallery forest providing shading and leaf litter input along the banks. Specific microhabitat data for K. savannensis at its type locality are not documented in the sources available, but related Knodus species from comparable savanna-edge habitats tend to use the mid-water and near-substrate zones in moderate current.
Feeding
FishBase records a trophic level of 3.2 (±0.4) for Knodus savannensis, placing it as a low-level predator or omnivore consistent with the feeding ecology of small characids generally. Specific dietary data for this species are not documented in available sources.
By analogy with related Knodus and small characids from comparable cerrado and transitional habitats, the diet likely includes small invertebrates — aquatic insect larvae, microcrustaceans, and zooplankton — as well as terrestrial arthropods falling onto the water surface and possibly some plant or algal matter. In captivity, related species accept fine live and frozen foods, small pellets, and flake; a varied diet supports health and colour.
Mating
No specific reproductive or courtship behaviour data are documented in available sources for Knodus savannensis. As a characid from an open-water floodplain and savanna-river context, the species almost certainly follows the general characid reproductive strategy: egg-scattering with no parental care, spawning triggered by seasonal cues such as rising water levels and temperature shifts during the wet season.
Related small Knodus species, like other open-water characids, are presumed to spawn in groups over vegetation or submerged structure, releasing semi-adhesive or non-adhesive eggs broadcast into the current or settling among fine-leaved plants and leaf litter. Males and females are distinguished by body proportions in most small Knodus, with females typically deeper-bodied when gravid, but specific dimorphism data for this species are sparse.
Breeding
Captive breeding records for Knodus savannensis are not documented in available hobby or scientific literature. The closely related Knodus borki has been bred in the aquarium under soft, acidic conditions — temperature in the 72–79 °F range, pH 5.5–7.0 — with fry requiring infusoria or similarly fine first foods. K. savannensis may have somewhat different requirements given its origin in the cooler, more seasonal cerrado drainage of the Tocantins, but specific data are lacking.
For aquarists wishing to attempt breeding, the general small-characid approach applies: condition the group on varied live and frozen foods, provide fine-leaved plants or spawning mops as egg-deposition sites, and remove adults after spawning. Eggs are small and the fry tiny at hatching; newly hatched brine shrimp and commercial micro-fry foods suit them once the yolk sac is absorbed.
In the aquarium
Knodus savannensis is a rarely encountered species in the hobby; it does not appear in mainstream trade lists and is unlikely to be available outside specialist importers or dedicated Characidae enthusiasts. Its small size (to 2.5 in TL) and presumed peaceful temperament make it theoretically suitable for a well-planted community tank of appropriate scale.
Based on its origin in the Tocantins basin's cerrado streams, a biotope-style setup with a sandy substrate, driftwood, and leaf litter would reflect its natural environment. Water conditions of moderate temperature (roughly 72–79 °F) and near-neutral to slightly acidic pH are a reasonable starting point, though data specific to this species are sparse. It should be kept in groups, as small characids are shoaling fish, and tankmates should be of similar scale and disposition.
Conservation
Knodus savannensis is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated November 2018. No specific population trends or threats are documented in the sources available for this assessment review.
The Tocantins basin has experienced significant hydrological modification — most notably the Tucuruí dam and subsequent hydroelectric development — which has altered flow regimes and fish assemblages in parts of the drainage. Whether these pressures affect K. savannensis at its specific localities is not documented. As a small, potentially widespread characid in a large river system, the Least Concern listing is plausible, but the species remains poorly known and would benefit from targeted survey work to clarify its distribution and abundance.