Home / Fishes / Tetras, piranhas and pacus / Sailfin tetra
No federal permit to keepSailfin tetra
Crenuchus spilurus
Fishes › Tetras, piranhas and pacus (Characiformes) › Crenuchidae (Darter tetras)
The sailfin tetra (Crenuchus spilurus), also known as the mojarita, is a species belonging to the South American darter family, Crenuchidae.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 2.2 in / 5.7 cm).
- Water: Freshwater.
- Temperature: 75–82°F (range recorded for this species).
- pH: 5.5–6.5.
- Hardness: 0–5 dGH.
- Layout: An open-water swimmer: needs long, open swimming space with few obstacles.
- Diet: A predator: feed meaty foods sized to its mouth (frozen fish, shrimp, worms); it will eat tankmates that fit in its mouth. FishBase classes it as a carnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 30 × 12 in (roughly 18 US gallons); space needed is rated “modest tank”.
- Water: soft, acidic water, 68–82 °F, pH 4–6.5, 1–5 dGH.
- Behaviour: temperament peaceful; in a pair; not a community fish.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Best-maintained in a well-structured set-up, ideally comprising a sandy substrate plus some driftwood roots and branches.”
- Diet: “Chiefly a micropredator feeding on tiny invertebrates and other zooplankton with the stomach contents of wild specimens from Guyana observed to comprise Ephemeroptera larvae, copepods and ostracods.”
- Tankmates: “Peaceful with other species but does not always make an ideal community fish due to its rather timid nature and predominantly benthic existence.”
- Breeding: “Normally spawns in small caves or among leaf litter and forms temporary pair bonds with the male solely responsible for egg and brood-care.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Darter tetras
Applies to most species in this group. Habitat: These South American freshwater fishes include shaded leaf-litter rainforest-stream Poecilocharax and darters from Brazilian and Amazon–Orinoco drainages. [fg180-morpho, fg180-char, fg180-ammo]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- Poecilocharax weitzmani pair or single-male harem: at least a 45 × 30 cm footprint.
- Additional males: at least 30 × 30 cm territory each, with refuges.
- Poecilocharax: soft sand, leaf litter, roots and spawning caves.
- Poecilocharax: dim lighting, gentle filtration and a mature aquarium.
- Poecilocharax: pH 3.0–6.5 and 0–5 dGH; not a family-wide prescription.
Climate & lighting
| Water | 69.8–82.4°F |
Diet
- Poecilocharax: live Daphnia and Artemia.
- Poecilocharax: grindal worms or microworms.
- Poecilocharax: chopped bloodworms; dried foods are often refused.
Social life
- Poecilocharax do not school; males defend territories. Keep more females than males and avoid competing bottom fish.
Health watch
- Wasting after import and food refusal.
- Fin damage from territorial males.
- Water-quality-associated gill or skin disease; a general aquarium-fish risk rather than documented family-specific prevalence.
Understanding the animal
About this animal
About this animal
It is found in the Amazon and Orinoco Basins, as well as various river Basins in the Guianas. It is the only member of the monospecific genus, Crenuchus, one of two genera within the subfamily Crenuchinae.
Quoted from the Wikipedia article “Sailfin tetra” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater, in rivers and streams, mangroves. Little is known of its biology in its natural environment. Unlike most Characoids, this species is typically solitary and territorial. The dimensions of the mouth confirms its predatory habits. Its food consists mainly of Ephemeroptera larvae, copepods and ostracods. In the aquarium, only the male guards the spawned eggs. About a hundred eggs are deposited on the substrate and dispersed by the male. |
| Water it lives in | Freshwater, 75–82 °F (24–28 °C), pH 5.5–6.5, hardness 5 dH. |
| Climate | Tropical climate. |
| Wild diet | Hunting macrofauna (predator). |
| Behavior to plan for | Breeding: brood hiders. |
What this means for care
- Keep water within its wild range, 75–82 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 90°F (up to 92°F in the hottest sampled areas) |
| Cool-season lows | about 71°F (down to 69°F in the coldest sampled areas) |
| Average temperature | 78–81°F across sampled records |
| Relative humidity | 81–85% on average (driest month about 78%) |
| Rainfall | about 2412 mm a year |
Measured at 254 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The sailfin tetra (Crenuchus spilurus), also known as the mojarita, is a species belonging to the South American darter family, Crenuchidae. It is found in the Amazon and Orinoco Basins, as well as various river Basins in the Guianas. It is the only member of the monospecific genus, Crenuchus, one of two genera within the subfamily Crenuchinae. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Behavior | The sailfin tetra, as a tiny species, is unlikely to participate in active dispersal across long distances. This is clear from its absence in the main channel of huge rivers. Active migration in open areas, particularly in a predator-rich environment like the Amazon basin, presents unique obstacles for small, non-schooling fish. — Wikipedia (community-edited) |
| Biology | Little is known of its biology in its natural environment. Unlike most Characoids, this species is typically solitary and territorial. The dimensions of the mouth confirms its predatory habits. — FishBase |
| History and naming | The sailfin tetra was first formally described in 1863 by the German-born British ichthyologist Albert Günther with its type locality given as the Essequibo River in Guyana. When he described this species, Günther proposed the new monospecific genus Crenuchus. — Wikipedia (community-edited) |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Adult length
Maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 30 × 12 in (about 18 US gallons).
Sources for this sheet
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Seriously Fish: Poecilocharax weitzmani Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- FishBase: Characidium fasciatum Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- FishBase: Ammocryptocharax elegans Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Disorders and Diseases of Fish Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.