Home / Fishes / Gars / Alligator gar
No federal permit to keepAlligator gar
Atractosteus spatula
Fishes › Gars (Lepisosteiformes) › Lepisosteidae (Gars)
The alligator gar (Atractosteus spatula) is a euryhaline ray-finned fish in the clade Ginglymodi of the infraclass Holostei, being most closely related to the bowfins.
Care at a glance
Species-specific aquarium care
- Tank: An adult reaches about 78.7 in (200 cm). That needs a pond or public-aquarium-scale system, far beyond a home aquarium.
- Water: Freshwater (tolerates brackish).
- Layout: Lives on or near the bottom: floor space and hiding places matter more than height.
- 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.
- Availability: Mostly kept by public aquariums; private keeping is uncommon.
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: a fairly wide range, from slightly acidic to slightly alkaline, 52–73 °F, pH 6–8, 5–25 dGH.
- Behaviour: kept alone; not a community fish.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Relatively unfussy provided water flow is not too strong and lighting not bright.”
- Diet: “Gars are ambush predators feedimg on smaller fishes and aquatic crustaceans in nature.”
- Tankmates: “Best kept alone, or with similarly-sized, non-aggressive fishes it cannot fit into its mouth.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Gars
Applies to most species in this group. Habitat: The listed gars inhabit North American lakes, sluggish rivers, swamps and backwaters, often near vegetation, with some species also entering brackish water. [fg300-gar_adw, fg300-longnose_adw, fg300-shortnose_adw]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For alligator gar, plan a specialized pond or custom public-aquarium-scale installation; the keeper lists 1,000 US gallons or more, not an ordinary household tank.
- Keep the water surface accessible for atmospheric air gulping.
- Size the installation for the adult species: reported lengths reach 3 m in alligator gar, 1.83 m in longnose gar and 83 cm in shortnose gar.
- Maintain freshwater with ammonia and nitrite at zero; the alligator-gar keeper gives pH 6.8–7.8 and nitrate below 30 ppm.
Climate & lighting
| Water | 65–76°F |
Diet
- Suitably sized fish prey; alligator gar can be weaned onto frozen fish foods.
- Aquatic crustaceans, matching the family’s documented predatory diet.
Social life
- Choose companions too large to swallow; comparable body size is more important than the gar’s generally quiet behavior. Shortnose gar is described as solitary, so group housing is not obligatory.
Health watch
- Freshwater white spot and other external skin/gill parasites: general freshwater-fish risks.
- Bacterial skin disease or fin erosion associated with poor water quality and stress: general aquarium-fish risks.
Understanding the animal
About this animal
About this animal
It is the largest species in the gar family (Lepisosteidae), and is among the largest freshwater fishes in North America. The fossil record traces its group's existence back to the Early Cretaceous over 100 million years ago.
Quoted from the Wikipedia article “Alligator gar” (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, in rivers and streams. Stays near the bottom. Adults inhabit sluggish pools and backwaters of large rivers, swamps, bayous, and lakes. Rarely enter brackish and marine waters. |
| Water it lives in | Freshwater / brackish water. |
| Climate | Subtropical climate. |
| Wild diet | Hunting macrofauna (predator). |
| Behavior to plan for | Breeding: open water/substratum egg scatterers. |
What this means for care
- It tolerates or needs brackish water; check salinity needs before setup.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 93°F (up to 96°F in the hottest sampled areas) |
| Cool-season lows | about 39°F (down to 29°F in the coldest sampled areas) |
| Average temperature | 62–72°F across sampled records |
| Relative humidity | 67–74% on average (driest month about 67%) |
| Rainfall | about 1154 mm a year, spread fairly evenly |
| Winters | Cool to cold winters (lows around 39°F) in much of its native range. Seasonal slowdown may be relevant, but species-specific biology determines whether brumation or hibernation occurs. |
Measured at 274 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 alligator gar (Atractosteus spatula) is a euryhaline ray-finned fish in the clade Ginglymodi of the infraclass Holostei, being most closely related to the bowfins. It is the largest species in the gar family (Lepisosteidae), and is among the largest freshwater fishes in North America. The fossil record traces its group's existence back to the Early Cretaceous over 100 million years ago. — 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 |
| Social life and communication | Not much information is known about communication in alligator gars. — Animal Diversity Web |
| Wild diet | Alligator gars are opportunistic carnivores and sit-and-wait predators. — Animal Diversity Web |
| Behavior | Little is known about alligator gar behavior. — Animal Diversity Web |
| Reproduction | Mating behaviors in this species are not known. — Animal Diversity Web |
| Lifespan | Females generally live longer than males and are larger, they may live from 26 to 50 years in the wild (Etnier and Starnes, 1993). — Animal Diversity Web |
| Appearance and size | Alligator gar are grayish green to brown color on their dorsal surface and yellowish or white colored ventrally (Page and Burr, 1991). — Animal Diversity Web |
| Biology | Facultative air-breathing; Adults inhabit sluggish pools and backwaters of large rivers, swamps, bayous, and lakes. Rarely enter brackish and marine waters. They feed on blue crabs, turtles, waterfowl or other birds and small mammals. — FishBase |
| History and naming | Lacépède first described the alligator gar in 1803. The original name was Lepisosteus spatula, but was later changed by E.O. Wiley in 1976 to Atractosteus spatula to recognize two distinct taxa of gars. Synonyms of Atractosteus spatula include: Lesisosteus [sic] ferox (Rafinesque 1820), and Lepisosteus spatula (Lacepede 1803). — Wikipedia (community-edited) |
| Conservation | Alligator gar are not currently listed as endangered, threatened, or of special concern. — Animal Diversity Web |
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.
Maximum recorded lifespan
Longest recorded lifespan reported by each database; typical lifespans are usually shorter.
Typical adult weight
Average adult body mass in each database (FishBase gives the maximum recorded weight).
Adult length
Common length to maximum recorded length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates; aim for the middle.
pH
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.
- Animal Diversity Web: Lepisosteidae Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Animal Diversity Web: Lepisosteus osseus Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Animal Diversity Web: Lepisosteus platostomus Peer-reviewed researchAdded in the 2026 source-checked care-guide review.
- Aqua Imports: Alligator Gar, Atractosteus spatula Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Parasitic Diseases of Fish Zoo, university or veterinaryAdded 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.
- 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.