Home / Fishes / Killifish and livebearers / Potosi pupfish
No federal permit to keepPotosi pupfish
Cyprinodon alvarezi
Fishes › Killifish and livebearers (Cyprinodontiformes) › Cyprinodontidae (Pupfish)
Potosi pupfish (Cyprinodon alvarezi) is a species of fish in the family Cyprinodontidae.
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 1.7 in / 4.25 cm; the largest recorded was 2.0 in).
- Water: Freshwater.
- Temperature: 64–72°F (range recorded for this species).
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Availability: Rarely or never seen in the aquarium trade; expect to source it from specialists or not at all.
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, 63–79 °F, pH 7–8, 10–20 dGH.
- Behaviour: a shoaling fish best kept in a group of six or more; not a community fish.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Need not be too complicated so long as there are plenty of broken lines-of-sight.”
- Tankmates: “Best-maintained alone, especially if the intention is for the fish to breed, but can be maintained in a well-researched community provided sufficient space is available.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Pupfish
Applies to most species in this group. Habitat: These fish occupy shallow vegetated fresh or saline waters, ranging from Florida marshes to coastal lagoons and the isolated Devils Hole pool. [fg179-flag, fg179-sheep, fg179-fws]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For a flagfish pair, use at least a 60 × 30 cm footprint; groups need more room.
- Break sightlines with plants or spawning mops to provide cover between territorial males.
- Use sponge filtration when eggs or fry are present.
- Encourage filamentous algae for flagfish grazing.
- Flagfish: pH 6.5–8.5 and 2–20 dGH; establish species and population requirements before choosing fresh or saline conditions.
Climate & lighting
| Water | 64.4–86°F |
Diet
- Algae or an algae-containing prepared food for flagfish.
- Small live or frozen Artemia and Daphnia.
- Small bloodworms and other appropriately sized invertebrate foods.
Social life
- Flagfish males form territories; keep groups only with sufficient cover and space. Species-only maintenance is preferable for breeding.
Health watch
- Aggression injuries under overcrowded conditions; a general aquarium-fish risk.
- Ammonia-associated gill damage in inadequately cycled systems.
- Skin parasites or secondary bacterial infections introduced with new fish.
Understanding the animal
About this animal
About this animal
It is endemic to Mexico, but is now extinct in the wild, only surviving in captivity.
Quoted from the Wikipedia article “Potosi pupfish” (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. Uses both the bottom and open water. |
| Water it lives in | Freshwater, 64–72 °F (18–22 °C). |
| Climate | Subtropical climate. |
What this means for care
- Keep water within its wild range, 64–72 °F.
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 | Potosi pupfish (Cyprinodon alvarezi) is a species of fish in the family Cyprinodontidae. It is endemic to Mexico, but is now extinct in the wild, only surviving in captivity. — 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 |
| Appearance and size | Fin of nuptial male is white, milky or bluish white, the terminal black caudal fin bar is broad (wider than the pupil). Dorsal and anal fin of nuptial male has milky white edge, pelvic is bluish. Pectoral fins are grey-black. — Wikipedia (community-edited) |
| Biology | Not a seasonal killifish. Is difficult to maintain in aquarium. — FishBase |
| History and naming | The Potosi pupfish's scientific name Cyprinodon alvarezi honours Jose Alvarez del Villar (1903–1986) who had originally intended to describe the species, but had given the type, which he had collected in 1952, to Robert Rush Miller who took on the task of describing it. — 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
Common length to 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.
pH
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 24 × 12 in (about 14 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: Jordanella floridae Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- FishBase: Cyprinodon variegatus Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- US Fish and Wildlife Service: Inside Devils Hole Experienced keeper or breederAdded 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.
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