Harlequin vs Chili — Size, Colour, and Character
Harlequin rasboras (Trigonostigma heteromorpha) and chili rasboras (Boraras brigittae) share the same fiery copper-red colouration and schooling nature but differ dramatically in scale. Harlequins reach 4-4.5 cm, making them a medium small fish suited for 40L+ tanks. Chili rasboras are genuine nano fish reaching only 1.5-2 cm, placing them among the smallest schooling fish available for aquariums. The chili's name comes from its intense red colouration in males when well-conditioned — a saturated cherry-red with black lateral markings that rivals any marine fish for visual impact.
Temperamentally, both species are completely peaceful and will not bother any tankmate. The harlequin's black triangle patch on a golden body is its signature marking — this wedge-shaped blotch distinguishes it from lookalike rasboras like the lamb chop (Trigonostigma espei), which has a teardrop-shaped blotch instead. Chili rasboras lack the bold triangle marking; they are uniformly brilliant red with a thin dark lateral stripe. Under warm-spectrum LEDs and against dark substrate, a school of 15 chili rasboras creates one of the most visually striking effects possible in a nano aquarium.
Activity level differs significantly between the two. Harlequins are moderately active mid-water swimmers that move in loose schools. Chili rasboras are calmer and often hover nearly motionless in plant thickets when not actively schooling, giving them a jewel-like, ornamental quality. This calm behaviour also makes them ideal for observing natural schooling dynamics — a large school of chilies will spontaneously form a tight swarm when any disturbance occurs, then gradually relax back into individual exploration. Both species are available from specialist importers in Cambodia.
- ✦Harlequin rasboras are available at most Phnom Penh fish markets year-round — chili rasboras require ordering from specialist importers
- ✦Distinguish harlequin from lamb chop rasbora by patch shape: harlequin = right-angled triangle, lamb chop = curved teardrop
- ✦Under warm white LED lighting, chili rasboras display their most intense red — cool blue-white LEDs wash out the red pigment significantly
Tank Size and Setup for Each Species
Harlequin rasboras need a minimum 40L tank for a proper school of 8-10 fish, with 60L being the comfortable sweet spot that allows full natural swimming behaviour. They are mid-water swimmers that use all horizontal space, so a longer tank (60 cm+) is better than a tall one. They do well in moderately planted tanks with a mix of open swimming space and denser plant thickets at the sides and back. Water temperature 23-27°C with pH 6.0-7.5 suits them well — Cambodia's ambient temperature of 26-28°C is at the upper edge of comfortable but perfectly viable without a chiller.
Chili rasboras are true nano fish that can thrive in as little as 10L when kept as a species-only group, though 20-40L planted nano tanks are ideal. Their tiny size (1.5-2 cm) means they can be eaten by any fish over 5 cm — they must be kept only with similarly micro-sized tankmates. Ideal companions include pygmy corydoras, micro rasboras, pea puffers (species-only), and dwarf shrimp. In a planted nano tank, a school of 15-20 chili rasboras with a colony of red cherry shrimp creates a visually complete nano ecosystem that requires minimal maintenance.
Both species strongly prefer planted tanks. Bare tanks cause chronic stress — fish school more tightly in fear, colours fade, and breeding activity stops. For harlequins, a classic Takashi Amano-style aquascape with midground stem plants and open foreground suits their schooling pattern perfectly. For chili rasboras, a heavily planted "jungle" nano with mosses, anubias petites, and floating plants diffusing light creates conditions closest to their Borneo peat swamp origin. Dark substrate is important for both species — it reflects less light into their eyes and intensifies their red pigmentation.
- ✦Use black sand or dark ADA Aqua Soil for both rasbora species — colour improvement from dark substrate is dramatic and immediate
- ✦For chili rasboras, ensure no tankmate exceeds 3 cm — even peaceful medium fish will accidentally eat chili rasboras during feeding
- ✦A 30×30×35 cm cube tank with heavy planting and 20 chili rasboras is one of the best value nano setups available in Cambodia
Planted Tank Preference and Dim Lighting for Chili Rasboras
Chili rasboras originate from Borneo's peat swamp forests — one of the darkest freshwater environments on earth. The forest canopy blocks nearly all direct light, and the water is tea-black from tannins with a pH as low as 4.0. In captivity, replicating even a fraction of this subdued environment dramatically improves chili rasbora colour, confidence, and willingness to breed. Reduce lighting to 8-6 hours per day, use floating plants like salvinia or frogbit to diffuse surface light, and add Indian almond leaves to tint the water.
Harlequin rasboras are from the same region of Southeast Asia — Malaysia, Singapore, Thailand, and Sumatra — and share many of the same preferences, though they tolerate slightly brighter conditions than chilies. They naturally inhabit the margins of forest streams where overhanging vegetation creates partial shade. In Cambodia, many aquarists keep harlequins in community tanks lit for plant growth — this works but using a combination of shade-tolerant plants like java fern, anubias, and bucephalandra in the background creates the visual depth that makes harlequins look their best.
Planted tanks for both species benefit from CO2 injection, though low-tech tanks with slow-growing plants also work well. For chili rasboras, the plants serve a dual purpose: providing shade and spawning sites. Females scatter eggs among fine-leaved plants, particularly java moss and riccia, which the eggs cling to and develop in. In a heavily planted tank with soft, acidic water, chili rasboras spawn spontaneously and fry appear regularly among plant thickets without any dedicated breeding effort from the aquarist. This makes them unusually rewarding to keep.
- ✦Reduce photoperiod to 8 hours for chili rasboras — longer light periods suppress natural behaviour and breeding activity
- ✦Add salvinia or frogbit floating plants to diffuse surface light — these float freely, require no planting, and are sold cheaply at Cambodia plant markets
- ✦Java moss tied to driftwood provides both shelter and spawning sites for chili rasboras — a single baseball-sized clump is enough to trigger breeding
Feeding — Micro Pellets and Daphnia
Both rasbora species have small mouths adapted for tiny prey in the wild — zooplankton, micro crustaceans, and insect larvae. In captivity, the feed size matters as much as the feed type. Standard community flake food works for harlequins but should be crushed to flake fragments rather than fed as large flakes. For chili rasboras, standard flake is too large — their mouths cannot process pieces above 0.5 mm. Micro pellets specifically sized 0.2-0.5 mm (such as Hikari First Bites or New Life Spectrum 0.5mm) are ideal for daily feeding.
Live and frozen daphnia is the premium feed for both species. Daphnia (water fleas) triggers a feeding response that commercial food rarely matches — the moving particles activate natural hunting instincts, and the nutritional profile including natural colour enhancers causes a visible improvement in red pigmentation within 2-4 weeks of regular feeding. In Cambodia, live daphnia cultures can be maintained at home with minimal cost: a 10L container of aged water, some green water or algae, and weekly feeding of dried yeast will maintain a continuous harvest. Frozen daphnia blocks from Phnom Penh fish suppliers are a convenient alternative.
Feed twice daily in small amounts — what the fish can consume in 90 seconds. Overfeeding is the primary cause of water quality problems in planted nano tanks where biological filtration is gentle. For chili rasboras specifically, once-daily feeding is often sufficient given their tiny metabolic requirement. Baby brine shrimp (BBS) is another excellent food for both species and is the best conditioning food before breeding. BBS nauplii can be hatched at home from eggs using a simple saltwater tumbler — an essential skill for any Cambodia fishkeeper serious about breeding nano fish.
- ✦Crush standard flake food between your fingers before feeding harlequins — pre-crushed flake is absorbed more fully and produces less waste
- ✦Feed live or frozen daphnia twice weekly for best colour in both species — available frozen at most Phnom Penh aquarium shops
- ✦Start a home daphnia culture in a 10L bucket outdoors in Cambodia's sunshine — free live food within 2 weeks, self-sustaining indefinitely
Breeding on Plant Leaves
Harlequin rasboras have a unique spawning method: females deposit eggs on the underside of broad plant leaves, where they are fertilised by the male swimming alongside her in an inverted position. This upside-down spawning on leaf undersides is specific to Trigonostigma genus rasboras and makes them fascinating to observe. Preferred spawning plants include amazon sword, large-leaved anubias, and cryptocorynes. To trigger spawning, lower water temperature slightly by 1-2°C (simulate a rain event), raise TDS by adding 20% fresh RO water, and increase feeding with BBS or daphnia.
Chili rasboras scatter eggs among fine-leaved plants and java moss rather than placing them on leaf undersides. The fry are extremely small (under 2 mm when hatched) and require infusoria or commercial micro fry food for the first week before graduating to baby brine shrimp. In a heavily planted community tank, chili fry are virtually invisible and many are eaten. To raise fry successfully, transfer egg-laden moss clumps to a separate 10L breeding tank with gentle sponge filtration, dim lighting, and aged soft water. Fry appear in the moss within 5-7 days of spawning.
Breeding either species requires consistently soft, acidic water — this is the single factor most Cambodia-based aquarists miss. In hard tap water, egg hatch rates drop dramatically and fry that do hatch are weaker. A dedicated breeding setup using 70-100% RO water pH adjusted to 6.0-6.5 with peat or Indian almond leaf extract will raise spawn success rates to near-100%. The reward is worth the effort: a batch of 30-50 harlequin or chili rasbora fry raised to sellable size represents significant income for hobbyist breeders in Cambodia's growing ornamental fish market.
- ✦Place large anubias or amazon sword leaves horizontally near the tank bottom — harlequins prefer horizontal or slightly angled surfaces for egg placement
- ✦For chili rasbora breeding, use RO water at pH 6.0-6.5 with 1 Indian almond leaf per 5L — this replicates Borneo peat swamp chemistry
- ✦Sell surplus rasbora fry to Phnom Penh fish shops at 2-3 months old — the local market for quality nano fish is growing and underserved