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The Betta smaragdina, also known as the Alien Betta, is a small labyrinth fish valued for its emerald-green reflections and lively behavior. This wild species from Southeast Asia differs from Betta splendens through its more natural body shape, less exaggerated fins, and especially bright metallic coloration under subdued lighting. It inhabits calm, often shallow waters rich in vegetation and plant debris. Successful care requires warm, soft to slightly acidic water, a tightly covered aquarium, and peaceful tank mates. Because this is a wild-collected species, gradual acclimation and stable maintenance are especially important. Its moderate availability also makes it a rewarding choice for experienced aquarists.

General species description

The Betta smaragdina is a small wild fighting fish belonging to the genus Betta. It has a labyrinth organ that allows it to use atmospheric air, an adaptation suited to warm waters that may contain limited dissolved oxygen. Individuals are generally active, curious, and territorial, especially males toward one another. Their colors become more intense when the fish feels secure and has access to dense cover. The species displays a distinctive metallic green coloration and is much less artificially selected than domestic Betta splendens varieties. Its availability in the aquarium trade is moderate: it is less common than a domestic betta but is regularly sought by specialized aquarists. A quiet, planted setup helps preserve its natural behavior and reduces unnecessary stress.

Geographic origin and biotope

The Betta smaragdina occurs mainly in northeastern Thailand, in the Isan region, within watersheds associated with the Mekong basin. Populations are linked to ponds, ditches, rice fields, and small streams with little current. The habitat is often shaded by marginal vegetation, with soft water that may become amber from tannins. The bottom usually contains leaves, roots, and organic matter, while emergent or floating plants provide cover close to the surface. Natural conditions change with the seasons, but the species generally prefers warm, calm, slightly acidic water. Since it is a wild species, an aquarium modeled after this type of habitat encourages natural activity, surface use, and courtship behavior.

Precise locality and local name

The Betta smaragdina is associated with several localities in Isan, particularly northeastern Thailand, rather than with one uniform commercial strain. In everyday Thai usage, fighting bettas are called pla kat, a term that essentially means fighting fish. Local usage may vary by region and does not always refer exclusively to this species. In the aquarium trade, Alien Betta is mainly a commercial or vernacular name connected with its iridescent appearance, not a taxonomic rank. Fish from different localities may vary in color, pattern, and fin shape. For that reason, preserving locality information is valuable whenever it is available, especially for breeders interested in maintaining distinct lines.

Appearance and physical characteristics

The Betta smaragdina has an elongated body, a relatively broad head, and rounded to moderately extended fins. Its base color ranges from greenish brown to deep green, with reflective scales showing emerald-green to blue-green tones. The fins may display darker margins and bluish highlights. Adult males are usually more colorful and have longer fins than females, particularly during displays. The mouth is angled toward the surface, matching its lifestyle in calm water. As in several wild bettas, coloration intensifies during social interactions and breeding. Adult size remains modest, allowing the fish to be kept in a relatively compact aquarium when adequate floor space, cover, and surface access are provided.

General diet

In nature, the Betta smaragdina feeds mainly on small invertebrates and organisms found near the surface or among vegetation. In aquariums, it readily accepts frozen or live foods such as daphnia, brine shrimp, mosquito larvae, and small aquatic worms. A quality betta pellet can supplement the diet, but it should not be the only food offered. Meals should be small and varied, with portions limited so that no food remains uneaten. A protein-rich diet supports growth and coloration, while overfeeding quickly increases the risk of constipation and declining water quality. For good long-term condition, provide moderate portions, varied prey, and occasional fasting for adults.

Essential data

• Native river name: Mekong basin; several populations are associated with small streams in Isan.
• Local name used: Pla kat.
• Origin of the scientific name: Betta is a traditional name used for fighting fish; smaragdina refers to an emerald color.
• Etymology of the full name: Betta identifies the genus of fighting fish; smaragdina means emerald or emerald green.
• Common/vernacular names: Alien Betta, emerald betta, wild fighting fish.
• Family: Osphronemidae.
• Subfamily: Macropodinae.
• Name pronunciation: BET-ta smuh-RAG-di-na.
• Discovery: Described by Werner Ladiges in 1972.
• Maximum adult size: About 5 cm.
• Water temperature and pH: 24 to 28 °C; approximately pH 6.0 to 7.5.
• Stream appearance and surrounding vegetation: Calm or slow-moving shaded water with floating plants, dense vegetation, roots, and leaf litter.
• Typical tank mates: Small peaceful midwater fish, including calm rasboras and small cyprinids; avoid boisterous or fin-nipping species.
• Temperament and behavior: Curious and generally peaceful toward other species, but territorial between males; males may build bubble nests.
• Water depth: Shallow, often under 50 cm in suitable habitats.
• Sexual dimorphism: Males are usually more colorful with longer fins; females are often stockier and less brightly colored.
• Bottom structure and flow: Muddy or sandy-muddy bottom covered with leaves and plant debris; weak to nearly absent current.

In your aquarium

To keep the Betta smaragdina successfully, use a tightly covered aquarium with subdued lighting, dense plants, and several shelters near the surface. Maintain stable, warm water, perform regular partial water changes, and avoid strong currents. A male may be kept alone or with calm tank mates, but multiple males should not be placed together in a small aquarium. A varied diet, slow acclimation for wild specimens, and daily observation are the most important elements. A peaceful environment allows the fish to display its emerald-green reflections and natural behaviors to their full potential.