Taxonomy & naming
Trigonectes strigabundus was described by the American ichthyologist George S. Myers, with the type locality anchored to the Tocantins River basin at Porto Nacional, in what is today the state of Tocantins, Brazil. The date of publication appears as 1925 in some sources and 1926 in others; Eschmeyer's Catalog of Fishes is the authority governing the valid name, and the combination Trigonectes strigabundus Myers, 1926 is accepted here. The authority is not placed in parentheses because the species has not been moved from the genus in which Myers first described it.
The genus Trigonectes belongs to the family Rivulidae — the South American annual killifishes — within the order Cyprinodontiformes. Rivulidae is the largest family of annual killifish and contains the bulk of the seasonal-pool spawners native to South America. Trigonectes is a small genus of Neotropical annuals closely allied to other Cerrado and gallery-forest killifish; the limits of the genus and its species-level diversity have been reviewed periodically but remain incompletely resolved. FishBase records the species under ID 49683.
Morphology
FishBase records a maximum total length of 4.5 in, making Trigonectes strigabundus a moderately sized annual killifish — larger than the dwarf Nothobranchius species familiar to most hobbyists, but broadly comparable to the larger South American annuals such as Austrolebias. The body form is typical of the Rivulidae: elongated and slightly compressed, with a large mouth adapted for surface and mid-water feeding, and soft-rayed unpaired fins that in males are often enlarged and elaborately pigmented.
The specific epithet strigabundus describes the most prominent colour feature: according to ETYFish, it derives from striga (a streak or stripe) combined with the Latin suffix -bundus (connoting abundance or fullness), alluding to the series of brown spots aligned along each scale row to form a pattern of longitudinal streaks across the flanks. As in virtually all rivulid killifish, sexual dimorphism is pronounced — males carry the species' characteristic patterning in vivid form, while females are cryptically coloured with a plainer, spotted or barred body that makes them far less conspicuous in shallow, leaf-littered pool water.
Habitat
The native range of Trigonectes strigabundus is restricted to the Tocantins River basin in central Brazil, confirmed by ichthyological surveys documenting the endemic fauna of the Tocantins-Araguaia ecoregion. The Tocantins system drains the eastern Cerrado — the vast tropical savanna of the Brazilian interior — and its fisheries have been profoundly shaped by the alternation between a pronounced dry season, when small tributaries and lateral pools contract or disappear entirely, and a wet season that refills those habitats and connects them to the main drainage.
As an obligate annual, the species is specifically adapted to these seasonal pools and floodplain wetlands: shallow, soft-bottomed basins with accumulations of leaf litter, peat, and fine organic sediment that serve both as spawning substrate and as the medium in which diapausing eggs wait out the dry season. Water chemistry in Cerrado seasonal pools is typically soft and slightly acidic, reflecting the low-mineral soils of the biome, though precise physico-chemical data for this species remain sparse in the published literature. The IUCN assessment categorises the habitat as inland wetlands, and notes that the area, extent, and quality of those wetlands is declining.
Feeding
Like most South American annual killifish of comparable size, Trigonectes strigabundus is a generalist predator in the wild, foraging opportunistically on the invertebrate fauna of its shallow pool habitat: aquatic insect larvae, small crustaceans, worms, and surface-drifting terrestrial insects make up the bulk of the natural diet. The upturned jaw typical of the Rivulidae positions the mouth advantageously for surface feeding, and seasonal pool habitats generate pulses of invertebrate prey that coincide with the rains and the hatching of egg masses from a wide range of aquatic invertebrates.
In the aquarium the species is straightforwardly fed. Live and frozen foods — Daphnia, Artemia nauplii and adults, bloodworm, Tubifex — are accepted readily and provide the best condition and colour. Dried and pelleted foods can be offered as a supplement once fish are established; however, the species' natural diet is overwhelmingly invertebrate-based and a diet skewed toward live and frozen foods better matches its nutritional needs and stimulates natural behaviour.
Mating
Trigonectes strigabundus is an annual killifish, and its mating system reflects the fundamental reproductive strategy of that guild: pairs dive together into soft substrate — peat, mud, or accumulated detritus at the bottom of seasonal pools — and spawn directly within it. This diving or plunging behaviour, rather than scattering eggs onto plants or open water, is the defining character of annual spawning in the Rivulidae.
Males are reproductively active throughout the wet season and compete for access to females in their shallow pool territories. Courtship involves lateral displays and parallel swimming in which the male presents his patterned flanks and extended fins — a form of honest advertisement of condition and genetic quality. When a female accepts the display, the pair align side by side, briefly clasped, and dive in unison into the substrate, releasing eggs and sperm simultaneously a short distance below the sediment surface. Each spawning dive deposits a small clutch of eggs, and a single pair may perform multiple dives over the course of a day.
Breeding
The eggs of Trigonectes strigabundus are buried in the pool substrate and enter diapause — a state of developmental arrest that allows them to survive the dry season while the pool above them evaporates. Diapause in Rivulidae annuals operates at defined embryonic stages: eggs commonly pause at one or more specific developmental checkpoints, resuming development only when appropriate environmental cues (rewetting, in particular) lift the arrest. FishBase records an incubation period of approximately two months under aquarium conditions, though this figure represents the minimum development time after re-wetting and the total time from spawning to hatch — spanning the dry-storage period — is determined by the keeper's schedule.
In the aquarium, the standard method for annual rivulids applies directly: the spawning pair is kept over peat fibre or coconut coir into which they will readily dive; the medium is collected every few weeks, lightly pressed to remove excess water, sealed in a plastic bag with a small amount of moisture retained, and stored at room temperature for a period of four to ten weeks (or longer if early re-wetting produces no hatching). When the peat is re-wetted with conditioned, slightly soft and acidic water, hatchlings emerge over the following 24–72 hours. Fry are relatively large at hatching by killifish standards and can accept freshly hatched Artemia nauplii as a first food almost immediately. Growth is rapid; adults are short-lived in the wild, and in captivity many Rivulidae annuals complete their lifespan within twelve to eighteen months.
In the aquarium
Trigonectes strigabundus is described by Killi.co.uk as a peaceful species, suitable for both beginner and experienced killifish keepers, and appropriate for small aquaria given that it is a comparatively small fish relative to its maximum recorded size. These qualities — manageable size, undemanding temperament, and the intrinsic fascination of the annual lifecycle — make it a rewarding species for the dedicated killifish hobbyist, even if it is far less commonly encountered in the trade than the more widely kept West African Fundulopanchax or the Argentinian Austrolebias species.
Setup should mimic the species' natural environment: a shallow, well-planted aquarium with a soft substrate (peat or a fine inert sand mixed with peat fibre), low to moderate flow, and gentle filtration such as a sponge filter. Subdued lighting and a covering of floating plants reduce stress and encourage natural behaviour. Water should be soft and slightly acidic to neutral — consistent with Cerrado seasonal pool chemistry — and temperature maintained in the warm tropical range appropriate for a species from central Brazil. A tight-fitting lid is essential, as killifish are accomplished jumpers. The species is best kept either as a pair or in a group with a single male and two to three females to distribute male attention; multiple males may compete but are unlikely to cause serious injury in a well-decorated tank with adequate space.
As an annual species, individuals have a naturally limited lifespan, and maintaining the colony requires a regular peat-spawning programme to produce the next generation. Hobbyists working with South American annuals should expect to run two to three batches of incubating peat simultaneously to ensure a continuous supply of young fish and to guard against batch failure.
Conservation
The IUCN Red List assessed Trigonectes strigabundus as Endangered (EN) under criteria B2ab(iii), with an assessment completed in November 2018 and published in 2023. The B2 criterion identifies a restricted area of occupancy, and the ab(iii) qualifier signals both continuing decline and fragmentation across the species' small range. The population trend is listed as unknown, reflecting the absence of systematic monitoring data for this small and habitat-specialised fish.
The threats documented in the IUCN assessment are the characteristic pressures bearing on the Tocantins basin: residential and commercial development expanding across the Cerrado; mining activity affecting both water quality and the seasonal hydrology of small drainages; dam construction and water management interventions that alter the flood pulse on which annual species depend for habitat connection and egg hatching; and domestic and urban wastewater entering the small wetlands that constitute the species' range. The Tocantins basin has been heavily impacted by large hydropower projects — the Tucuruí Dam downstream and a cascade of smaller dams in the upper and middle basin — which have transformed the flood regime of the main channel and altered or eliminated the marginal seasonal pools that are the primary habitat of annual killifish.
No protected area is currently confirmed as covering the known range of Trigonectes strigabundus, and the IUCN assessment flags both population-status research and assessment of dam impacts as conservation actions needed. For a species with a reproductive strategy so tightly tied to the integrity of seasonal wetland hydrology, the alteration of that hydrology by water infrastructure represents an existential threat that cannot be mitigated simply by pollution control or harvest limits. Conservation of this species ultimately depends on the fate of the Cerrado's remaining seasonal pool ecosystems.