Betta Smaragdina (Emerald Betta) Care, Size & Lifespan

Betta Smaragdina
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Last Updated: July 18, 2023 by Flora Gibbins

Did you know that Betta can refer to more than the Betta splendens or Siamese Fighting fish? Or that there are dozens of cryptic species, including Betta smaragdina, that keepers breed and study?

We present this Betta smaragdina species guide to help you better understand one of the more popular fish in the B. smaragdina group.

Understanding the similarities and differences B. smaragdina has with B. splendens (and others in the bubble-nesting Betta genus) will further your appreciation and ability to care for this unique fish.

We hope that the following information offers you a look into type-locality B. smaragdina from eastern Thailand that can bring further enjoyment to your hobby.

Quick Facts

Size: 50 to 60 mm (1.97 to 2.37 inches)

Lifespan: 3 to 5 years in captivity

Ease of Care (Easy – Expert): Moderate care level

Native to: The Mekong and Chao Phraya basins

Minimum Tank Size: 5-gallon for one; 10-gallon for mating pair, 30-gallon community

Water Type: Freshwater fish

Temperature: Tropical range of 24 to 27-degrees Celcius (75 to 81-degrees Fahrenheit)

Compatibility: Best kept alone or as a mating pair; can cohabit with peaceful species in larger aquariums

Diet: Aquatic invertebrates in the wild; live/frozen foods and pellets

Betta Smaragdina Overview

B. smaragdina is a cryptic species related to the betta splendens. It is also known as the Blue Betta, Emerald Green Betta, or the Mekong Fighting fish within the fish-keeping industry.

So, what makes B. smaragdina unique? The standout feature of this fish is its colors.

Adult males are reddish-brown with blue and green iridescent spots on the scales. Anal and caudal fins on male Betta smaragdina can be blue and red, with faded stripes along the body. Female B. smaragdina colors are muted, with brown bodies and less prominent fin structures.

Betta smaragdina has a more peaceful disposition when compared to other Betta fish.

What is a cryptic species?

Many ecologists and evolutionists refer to cryptic species as animals that look similar but have genetics distinct from similar species. The B. smaragdina group is one of several fish that represent part of the larger bubble-nesting Betta genus.

Those who study animals recognize 72 distinct fish that are cryptic species that you would likely refer to as Betta fish.

The appearance of Betta Smaragdina

The B. smaragdina group is a smaller aquarium fish that measure up to 50 to 60 mm in length for males, with female Betta smaragdina 50 mm or shorter.

Wild-caught specimens (rarely seen in the industry) have a less prominent fin structure. Captive-bred B. smaragdina represents generations of breeding to create large plummed fins that display blue with red rays extending from the body to the end of its tails.

Most fish in the B. smaragdina group has a red body. The scales of the males have iridescent tips that display blue or green colors. That is what gives Betta smaragdina its unique look.

The iridescent colors may be less noticeable along the bottom or top of the fish, giving males the appearance of lighting stripping along the body.

A slightly upturned jaw is noticeable on B. smaragdina. The gill plate (operculum) has a similar blue or green color as the iridescent scale tips.

Female Betta smaragdina have smaller anal, caudal, and dorsal fins. The body colors are brown, with two black stripes along the body. Adult females are visually smaller in length and fin size when compared to adult males throughout the B. smaragdina group.

Betta Smaragdina Lifespan, Habitat / Tank Size & Requirements

Type-locality B. smaragdina from eastern Thailand have been bred as fighting fish for hundreds of years. That said, you will find it lacks data gathered from the study given to other Betta, such as B. splendens.

Betta smaragdina have a similar lifespan in captivity as Siamese Fighting fish. That will give you two to four years with your pet (depending upon how old it is when you get it). Several B. smaragdina live between three and five years under optimal tank conditions.

Tank requirements

Even if you buy your fish in a cup or bowl, it will need at least a five-gallon fish tank to stay healthy and have longevity. A larger 10-gallon aquarium should be the smallest environment you offer a breeding pair (study your pet’s behavior to determine if they need more space). Community tank settings require at least a 30-gallon aquarium, depending upon the number of fish you want to keep.

Betta smaragdina are known to have a more peaceful disposition when compared to other type-locality B. smaragdina hailing from the Chao Phraya or Mekong basins. They are Mekong Fighting fish, however, so aggression is possible within crowded tanks. Study how your Betta smaragdina act towards other fish and remove tank mates that are not compatible.

Betta smaragdina habitat

The delta environments that the fish hail from makes this species and other types like Betta macrostoma favor a planted tank.

Your Betta is territorial, so offering your fish one or more hiding places is a must. They will use underwater structures to help establish their territory, and it will also provide a retreat when it feels stressed.

Betta Smaragdina Care

Your Betta is a freshwater fish, which many beginners feel is easier to maintain. It is a tropical fish, so a heater will help you keep water temperatures between 24 and 27 C (75 and 81 F). Maintain strong biological filtration, and add both chemical and mechanical filters for improved water conditions where needed.


Give your pet food twice a day. Avoid overfeeding by adding no more food than can be eaten in two minutes.

Feed your Betta smaragdina live or frozen meat-based proteins, including bloodworms. We recommend frozen unless you can source live food from a reputable dealer (to avoid possible infections).

Most captive-bred Betta smaragdina will also eat pellet foods. That allows you to introduce some plant matter into their meals for a balanced diet. Just make sure to feed them plenty of meat proteins as well.

Smaragdina Group Breeding

These are members of the bubble-nesting Betta genus, so a paired male and female have mating potential.

Keep the temperature near the higher end of tolerance. Study your female, her color lightens, and she gains vertical bars on the body. Then the male betta makes a bubble nest.

Once they mate, the male will place the eggs in the nest, and they should hatch within a couple of days. The male will care for them until they are free-swimming fry at about five days.


Betta smaragdina are rare in the industry when compared to other Betta. That will make them a more expensive fish when you can find them. You will likely have to buy from a local breeder, which can reduce the price (and survivability) over online purchases abroad.

Are Betta Smaragdina Right For You?

Yes! The species is no more complex than other tropical fish. Those looking for a colorful pet that stands out with iridescent colors will appreciate fish from the B. smaragdina group.

Things to consider include:


  • Colorful
  • Rare


  • Pricey

If you have any questions or comments for us, make sure that you leave them below!

Betta smaragdina a.k.a. Emerald Betta or Blue Betta

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