Home / Fishes / Killifish and livebearers / Redtail splitfin
No federal permit to keepRedtail splitfin
Xenotoca eiseni
Fishes › Killifish and livebearers (Cyprinodontiformes) › Goodeidae (Goodeid livebearers and killifish)
The redtail splitfin or redtail goodeid (Xenotoca eiseni) is a species of goodeid fish from the family Goodeidae and subfamily Goodeinae.
Care at a glance
Species-specific values
Values researched for this exact species. Where they differ from the group guide below, follow these. Air, surface and water temperatures are listed separately, and each source is kept as published rather than averaged.
| Water temperature | 59–86 °F (15–30 °C) Maintenance recommendations from this source; do not replace with a multisource average. | 264 |
| Water pH | 6–8 Maintenance recommendations from this source; do not replace with a multisource average. | 264 |
| Water general hardness | 10–20 dGH Maintenance recommendations from this source; do not replace with a multisource average. | 264 |
| Adult standard length | 60 mm Maximum standard length reported by source; excludes caudal fin, not total body length. | 264 |
| Minimum tank base | length: 60 cm; width: 30 cm Minimum aquarium base recommended by this source, not a tank-volume specification. | 264 |
| Social | Species aquarium preferred because individual fish can attack or severely nip other species. | 264 |
| Reproductive mode | Live-bearing goodeid; developing young receive maternal nourishment via trophotaeniae. Not an annual peat-spawning killifish. | 264 |
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 2.4 in / 6 cm).
- Water: Freshwater.
- Temperature: 59–90°F (range recorded for this species).
- pH: 6–8.
- Hardness: 9–19 dGH.
- Layout: Lives on or near the bottom: floor space and hiding places matter more than height.
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 24 × 12 in (roughly 14 US gallons); space needed is rated “modest tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 59–86 °F, pH 6–8, 10–20 dGH.
- Difficulty: Beginner (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “A densely planted aquarium with a dark substrate will allow these fish to exhibit their colours to the best effect.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Goodeid livebearers
Applies to most species in this group. Habitat: Mexican freshwater streams and springs; preserve population identity. [gwg-xenotoca-eiseni]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For a colony, Goodeid Working Group recommends at least 250 L, generous floor space, moderate current, rocks/roots, vegetation patches and open swimming areas.
- Seriously Fish instead lists 60 × 30 × 30 cm (~54 L); retain this disagreement rather than treating the small example as a conservation-colony standard.
- Seriously Fish lists pH 6–8 and hardness 10–20 dGH.
Climate & lighting
| Water | 68–75.2°F |
Diet
- Plant/algae-rich prepared foods and vegetables, supplemented with crustaceans/insect foods; diverse flake, granules and tablets are accepted.
Social life
- Species tank preferred: some individuals attack other fishes. Provide fry cover or separate rearing when fry are eaten. [sf-xenotoca-eiseni; gwg-xenotoca-eiseni]
Handling
- Minimize restraint; protect skin with nitrile gloves during necessary direct veterinary handling.
Health watch
- Monitor aggression and water quality; sustained temperatures above 77°F are discouraged by the Working Group.
Understanding the animal
About this animal
About this animal
Like other members of Goodeinae, the redtail splitfin is native to Mexico and a livebearer. However, the goodeid mating system differs in several ways from the more common livebearing fish from the family Poeciliidae that includes guppies and swordtails.
Quoted from the Wikipedia article “Redtail splitfin” (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. Stays near the bottom. |
| Water it lives in | Freshwater, 59–90 °F (15–32 °C), pH 6–8, hardness 9–19 dH. |
| Climate | Temperate climate. |
| Behavior to plan for | Breeding: internal live bearers. |
What this means for care
- Keep water within its wild range, 59–90 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 91°F (up to 96°F in the hottest sampled areas) |
| Cool-season lows | about 46°F (down to 42°F in the coldest sampled areas) |
| Average temperature | 64–76°F across sampled records |
| Relative humidity | 60–64% on average (driest month about 46%) |
| Rainfall | about 966 mm a year, with strong wet and dry seasons |
Measured at 14 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 redtail splitfin or redtail goodeid (Xenotoca eiseni) is a species of goodeid fish from the family Goodeidae and subfamily Goodeinae. Like other members of Goodeinae, the redtail splitfin is native to Mexico and a livebearer. However, the goodeid mating system differs in several ways from the more common livebearing fish from the family Poeciliidae that includes guppies and swordtails. While no goodeid species is a very popular aquarium fish, the redtail splitfin is one of the most popular. — 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 |
| Reproduction | Females can get young every 60 days. — FishBase |
| Appearance and size | The redtail splitfin is a deep-bodied fish, and males have a hump behind the head. The hump gets larger as the males get older. Adult males have a red-orange tail and tail-base. — Wikipedia (community-edited) |
| Biology | Migratory behaviour is undetermined. — FishBase |
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 24 × 12 in (about 14 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- Sharply Angled Lateral Curvature Modification in Anal Fin of a Viviparous Fish, Xenotoca variata (Cyprinodontiformes: Goodeidae) Iida A et al., Zoological science 2021
- Ontogeny and Dynamics of the Gonadal Development, Embryogenesis, and Gestation in Xenotoca eiseni (Cyprinodontiformes, Goodeidae) Tinguely SM et al., Sexual development: genetics, molecular biology, evolution, endocrinology, embryology, and pathology of sex determination and differentiation 2019
- Production of live young with cryopreserved sperm from the endangered livebearing fish Redtail Splitfin (Xenotoca eiseni, Rutter, 1896) Liu Y et al., Animal reproduction science 2018
Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. 170
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.
- Goodeid Working Group: “Xenotoca” eiseni, identification and husbandry Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Xenotoca eiseni Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
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