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No federal permit to keepBlue betta
Betta smaragdina
Fishes › Gouramis, bettas, snakeheads (Anabantiformes) › Osphronemidae (Gouramis and bettas)
Betta smaragdina, commonly known as the emerald green betta, blue betta or Mekong fighting fish (Thai: ปลากัดเขียว or ปลากัดอีสาน) is a species of gourami native to Southeast Asia.
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 2.8 in / 7 cm).
- Water: Freshwater.
- Temperature: 75–81°F (range recorded for this species).
- pH: 6–8.
- Hardness: 5–19 dGH.
- 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
- Tank: a base of at least 18 × 12 in (roughly 11 US gallons); space needed is rated “modest tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 72–82 °F, pH 5.5–7.5, 1–10 dGH.
- Behaviour: temperament species tank; in a pair; not a community fish.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “This species fares best in a well-planted, shady aquarium with plenty of surface cover in the form of tall stem plants, floating types such as Salvinia or Riccia spp., or tropical lilies from the genus Nymphaea.”
- Diet: “Likely to prey on aquatic and terrestrial invertebrates in nature.”
- Tankmates: “Not recommended for the standard community aquarium.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Bettas (fighting fish)
Applies to most species in this group. Habitat: Shallow rice paddies and marshes. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- A heated, filtered tank of at least 5 gallons, with gentle flow and plants.
- Domestic B. splendens should generally be maintained alone. Other Betta species need their own compatibility plan; B. imbellis can be maintained as a pair with adequate cover.
Diet
- Betta pellets plus frozen foods.
Social life
- Use species-specific social housing: B. splendens alone under the detailed Seriously Fish recommendation; B. imbellis may be housed as a compatible pair.
Health watch
- Fin rot in dirty water; never keep bettas in tiny unheated bowls.
Understanding the animal
About this animal
About this animal
The species gets its green and blue colors due to refraction and interference of light that results from hexagonal crystals that are less than 0.5 micrometres. It is found in the aquarium trade.
Quoted from the Wikipedia article “Betta smaragdina” (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, 75–81 °F (24–27 °C), pH 6–8, hardness 5–19 dH. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: nesters. |
What this means for care
- Keep water within its wild range, 75–81 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 95°F (up to 97°F in the hottest sampled areas) |
| Cool-season lows | about 61°F (down to 56°F in the coldest sampled areas) |
| Average temperature | 77–81°F across sampled records |
| Relative humidity | 70–73% on average (driest month about 60%) |
| Rainfall | about 1420 mm a year, with strong wet and dry seasons |
Measured at 44 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 | Betta smaragdina, commonly known as the emerald green betta, blue betta or Mekong fighting fish is a species of gourami native to Southeast Asia. The species gets its green and blue colors due to refraction and interference of light that results from hexagonal crystals that are less than 0.5 micrometres. It is found in the aquarium trade. — 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 |
| Wild diet | In the wild, Betta smaragdina feeds on terrestrial and aquatic invertebrates. In captivity, it is typically fed live or frozen food like Daphnia, Artemia or bloodworms. — Wikipedia (community-edited) |
| Reproduction | Male individuals of Betta smaragdina will build a bubble nest before breeding. The temperature at which breeding typically occurs is 25.6 to 26.7 C. Males and females can live together and the male and female should already live together for breeding. When the female is interested in mating, she becomes lighter coloured and develops vertical bars. — Wikipedia (community-edited) |
| Appearance and size | Betta smaragdina grows to a maximum total length of 7 cm. — Wikipedia (community-edited) |
| Biology | Facultative air-breathing; Bubble nest builder. — FishBase |
| Conservation | Betta smaragdina is listed as data deficient by the IUCN. It is uncommon throughout its range and the population of the species is still decreasing. It is threatened by habitat destruction, pollution, and hybridization with escaped domesticated bettas. — 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.
Minimum tank footprint
Seriously Fish recommends a tank base of at least 18 × 12 in (about 11 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.
- Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Types and features of aquatic systems Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Nutritional diseases of fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Seriously Fish — Betta splendens Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Seriously Fish — Betta imbellis 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.
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