Home / Fishes / Killifish and livebearers / Diamond killifish
No federal permit to keepDiamond killifish
Fundulus xenicus
Fishes › Killifish and livebearers (Cyprinodontiformes) › Fundulidae (Topminnows and killifish)
The diamond killifish (Fundulus xenicus) is a species of North American killifish found in salt marshes, hypersaline flats and mangrove along the Gulf Coast of the United States.
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 2.4 in / 6 cm).
- Water: Freshwater (tolerates brackish).
- Temperature: 81–95°F (range recorded for this species).
- pH: 7.5–8.5.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
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
- Water: hard, alkaline water, 70–95 °F, pH 7.5–9, 10–30 dGH.
- Behaviour: a shoaling fish best kept in a group of six or more; not a community fish.
- Difficulty: Easy (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Even for long-term maintenance a simple set-up will suffice.”
- Diet: “A generalised omnivore feeding on small organisms from submerged vegetation or the water surface.”
- Tankmates: “Not a good choice for the community aquarium given its water chemistry requirements and rarity in the hobby, and we strongly recommend maintaining it alone.”
- Breeding: “Captive reproduction is not normally difficult if the tank or container is properly arranged and maintained (see 'tank set-up').”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Topminnows and killifish
Applies to most species in this group. Habitat: North American fundulids inhabit vegetated fresh waters and coastal marshes or estuaries, with habitats and salinity differing by species. [fg203-fb-chrysotus, fg203-fb-goodei, fg203-adw-mummichog]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- Fit a complete cover: mummichogs and other killifish jump.
- Provide submerged vegetation and smooth cover; a mummichog breeding account used hornwort, smooth river rocks, and a floating spawning mop.
- Use freshwater for golden topminnows and vegetated habitat for bluefin killifish; reproduce the collection population's salinity for coastal mummichogs instead of routinely salting every fundulid tank.
- Use established filtration, bottom waste removal, and regular partial water changes; avoid crowding growing fry.
- For scale, a published F. heteroclitus/F. majalis laboratory protocol held cohorts in 475 L aquaria at 31–33 ppt; this is a research setup, not a universal household minimum.
Climate & lighting
| Water | 68–71.6°F |
Diet
- Small insect foods for Fundulus chrysotus, which feeds primarily on insects.
- Brine shrimp and appropriate flake food for acclimated mummichogs.
- Chopped earthworms for adult mummichogs; newly hatched brine shrimp or microworms for their fry.
- Copepods and small worms for Lucania parva.
Social life
- Mummichogs naturally school, but spawning males can harass females; provide cover and monitor breeding groups. Separate eggs from adults, which eat spawn. Do not combine small Lucania with larger predatory fundulids solely because they share a family. [fg203-adw-mummichog, nanfa-mummichog; compatibility precaution inferred from size and predation]
Health watch
- Freshwater ich or marine Cryptocaryon, according to the system's salinity; general fish risks, not documented family-specific prevalence.
- Saprolegnia water-mold infection of freshwater eggs or injured skin.
Understanding the animal
About this animal
About this animal
This species grows to a length of 6 cm (2.4 in). It is found in the aquarium trade.
Quoted from the Wikipedia article “Diamond killifish” (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 and brackish water and the sea. Uses both the bottom and open water. Occur from fresh water to hypersaline flats, salt marshes and mangrove areas. |
| Water it lives in | Freshwater / brackish water / marine, 81–95 °F (27–35 °C), pH 7.5–8.5. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: open water/substratum egg scatterers. |
What this means for care
- Keep water within its wild range, 81–95 °F.
- It tolerates or needs brackish water; check salinity needs before setup.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 91°F (up to 92°F in the hottest sampled areas) |
| Cool-season lows | about 45°F (down to 41°F in the coldest sampled areas) |
| Average temperature | 67–75°F across sampled records |
| Relative humidity | 73–75% on average (driest month about 70%) |
| Rainfall | about 1365 mm a year, spread fairly evenly |
Measured at 89 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 diamond killifish (Fundulus xenicus) is a species of North American killifish found in salt marshes, hypersaline flats and mangrove along the Gulf Coast of the United States. This species grows to a length of 6 cm. It is found in the aquarium trade. It was previously recognized as, Adinia xenica, the only known member of the genus Adinia. — 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 | Maximum length 6.0 cm tl male/unsexed. — FishBase |
| Biology | Occur from fresh water to hypersaline flats, salt marshes and mangrove areas, commonly in shallow water less than 0.3 m in depth. Not a seasonal killifish. Is difficult to maintain in aquarium. — 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
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.
- Hal Fairfield, NANFA American Currents: Breeding Fundulus heteroclitus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Animal Diversity Web: Fundulus heteroclitus Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- FishBase: Fundulus chrysotus, Golden topminnow Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- FishBase: Lucania goodei, Bluefin killifish Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- FishBase: Lucania parva, Rainwater killifish Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Hypoxia Tolerance of Two Killifish Species: animal husbandry methods Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- NANFA: Welcome to NANFA, native fish keeping and collecting Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- MSD Veterinary Manual: Parasitic 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.
- 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.