Slim Betta / Slender Betta (Betta bellica)

Slim Betta / Slender Betta overview

Slim Betta / Slender Betta (Betta bellica) is a wild-type labyrinth fish with a long, elegant body shape and a calm but unmistakably territorial surface presence. It is a very different proposition from a heavily finnaged domestic betta: the appeal is in the natural shape, confident behaviour and peat-swamp character rather than oversized fins.

This 4 cm size is a young specimen that can grow on into a larger wild betta. FishBase records Betta bellica from Indonesia and Malaysia, with a tropical temperature range of 24-30 C and a maximum length up to around 10 cm total length. In the aquarium trade it is often called Slim Betta, Slender Betta or Bellica Betta.

Quick facts

• Scientific name: Betta bellica
• Common names: Slim Betta, Slender Betta, Bellica Betta
• Current size: around 4 cm
• Adult size: commonly around 8-10 cm with mature males the larger fish
• Temperature: 24-30 C
• pH: best kept soft and acidic to neutral; FishBase lists 6.5-7.5, while specialist wild-betta care often uses lower acidic blackwater-style conditions
• Minimum aquarium: 75 litres recommended for stable water, surface cover and careful tank-mate choice
• Diet: carnivore; small floating pellets plus frozen or live foods
• Temperament: semi-aggressive, territorial, especially near the surface and during breeding

Appearance and behaviour

The original reference photo shows a slim golden-green fish with darker edging through the unpaired fins, a pointed surface-feeding profile and a more natural wild-betta look than domestic long-fin strains. Colour can deepen with maturity, diet, tannin-rich surroundings and confident settling-in time. Young fish may look understated at first, which is normal for many wild-type bettas.

The name suits the fish. Betta bellica has a noticeably slender outline, a strong surface-oriented posture and proportionate fins that make it look clean and athletic rather than ornamental. The reference photo shows the golden-green body tone and darker fin edging that make this species attractive without looking artificial.

Expect a fish that patrols the upper level of the aquarium, watches movement outside the glass and claims cover near the surface. It is not a background species. Males can be more colourful and more assertive, and the species should be treated as territorial even when it seems calm.

Natural-style aquarium setup

Think habitat first. Wild Betta bellica is associated with swamp forest and peat-swamp style waters, so the display should feel sheltered rather than exposed. Floating plants, overhanging stems, wood, leaf litter and darker background tones all help the fish feel secure. Leave breathing spaces at the surface rather than covering every inch.

A warm, covered, planted aquarium is the right direction for this species. Use gentle filtration, subdued lighting, floating plants, wood, leaf litter or botanicals if your setup suits them, and open pockets at the surface for breathing. Like other labyrinth fish, Slim Betta uses atmospheric air, so the air above the water should stay warm and humid. A tight-fitting lid is essential because wild bettas can jump.

Water stability matters more than chasing exact numbers. Avoid harsh current, exposed bright tanks and fast surface competition. A mature aquarium with soft to neutral water, low stress and regular partial water changes will usually suit this fish far better than a bare, high-flow community tank.

Feeding

Slim Betta is carnivorous. Offer good small betta pellets or micro pellets as a base, then rotate frozen or live foods such as bloodworm, daphnia, brine shrimp, mosquito larvae and small insect larvae. Feed modest portions once or twice daily so food is eaten quickly and water quality stays clean.

Variety is useful because it supports colour, condition and breeding behaviour. Surface feeding is natural for this species, but do not keep it with very fast surface feeders that take every meal before the betta has settled.

Tank mates and compatibility

Buyer fit matters with this fish. It is a good choice for a fishkeeper who enjoys natural behaviour, covered planted tanks and slower observation. It is less suitable for a bright, busy community aquarium where every fish rushes the surface at feeding time.

This is a semi-aggressive wild betta, not a general mixed-community fish for every tank. The best companions are peaceful, non-nippy species that use different levels of the aquarium and enjoy similar warm, calm water. Small bottom dwellers may work in a larger, heavily planted aquarium, but the setup must give each fish space.

Avoid other male bettas, fin nippers, large predators, aggressive cichlids and boisterous surface feeders. Small shrimp may be eaten. If you want to keep a pair or group, plan the aquarium around cover, line-of-sight breaks and observation rather than assuming all individuals will tolerate each other.

Breeding notes

Betta bellica is a bubble-nesting betta. In suitable warm, quiet water, the male builds and guards a floating nest, usually under surface cover. Breeding attempts should be kept calm, clean and low disturbance, with floating plants or similar shelter. Adults and fry need excellent water quality and appropriately small foods.

Acclimation and first week

Acclimate slowly, keep the lights low on arrival and avoid chasing the fish around the tank once released. Give it cover near the surface from day one. During the first week, watch appetite, breathing, colour, fin posture and whether it is using the top level confidently. Do not make sudden pH or hardness changes after arrival; stable clean water is safer than quick adjustment.

Buying from Tropical Fish Co

Order this Slim Betta / Slender Betta with specialist live-fish packing, tracked UK live-animal courier delivery and our Live Arrival Guarantee. New customers can use WELCOME10 for 10% off their first order. We preserve the exact product media and care notes for each listing so you can buy with a clearer view of the fish and its requirements.