Fire Ant Tetra

Quick summary

The fire ant tetra (Hyphessobrycon myrmex) is a tiny, strikingly coloured characin only formally described in 2013. It is best suited to experienced hobbyists who can maintain soft, acidic water and who appreciate nano species in a mature, well-planted aquarium. Because it was described so recently and aquarium literature remains thin, some care recommendations below are informed by closely related Hyphessobrycon species; where this is the case, the text says so plainly.

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Last researched and fact-checked: June 2025.

• Introduction
• Quick Stats
• Appearance
• Natural habitat
• Tank size and setup
• Water parameters
• Filtration and equipment
• Diet and feeding
• Behaviour and temperament
• Tank mates
• Breeding
• Common diseases and health
• Frequently asked questions
• Related guides

Introduction

Hyphessobrycon myrmex was formally described by Marinho and Lima in 2013, with the species epithet myrmex derived from the Greek word for ant, a reference to the deep red and black colour pattern that calls to mind a fire ant. It is one of the smallest described members of the genus Hyphessobrycon, with adults reaching only around 2 cm standard length (SL). The species originates from the Rio Aripuanã basin in the state of Mato Grosso, Brazil, a tributary system of the Rio Madeira within the greater Amazon drainage.

Despite its attractive colouration and diminutive size making it an appealing candidate for nano aquaria, the fire ant tetra remains uncommon in the hobby. It appears only sporadically in specialist importers’ lists, and published husbandry information specific to this species is limited. Most of what aquarists know about keeping it is extrapolated from broader Hyphessobrycon care, supplemented by the handful of hobbyist accounts that exist. This guide attempts to present what is genuinely documented and to be transparent wherever recommendations rest on inference from related species rather than direct observation of H. myrmex itself.

The common name “fire ant tetra” is widely used in the hobby and trade, though it does not appear to have been coined in the original scientific description. It is, however, the name by which the species is almost universally known among English-speaking aquarists.

Appearance

The fire ant tetra is a strikingly pigmented fish for its size. The body is deep red to reddish-orange, overlaid with bold black markings. A prominent dark blotch sits on the humeral (shoulder) region, and a second, often more conspicuous, dark marking is present on the caudal peduncle, sometimes extending into the base of the tail fin. The combination of vivid red ground colour and contrasting black patches is the basis for the common name, evoking the appearance of a fire ant.

The body shape is typical of many small Hyphessobrycon: laterally compressed and moderately deep relative to its length. The fins are largely translucent to lightly tinted with red or orange. Males in breeding condition often display more intense colouration, though detailed descriptions of sexual dimorphism in this species specifically are sparse in the literature. In many related Hyphessobrycon species, mature females tend to be slightly fuller-bodied, and this is likely true for H. myrmex as well, but this observation should be treated as an inference rather than a firmly documented fact for this particular species.

At roughly 2 cm SL, this is one of the smallest formally described members of the genus. Total length, including the caudal fin, is likely around 2.5 cm, making it genuinely tiny. In a well-maintained aquarium with suitable water chemistry and a dark substrate, the red colouration can be exceptionally vivid.

Natural habitat

The type locality for Hyphessobrycon myrmex is within the Rio Aripuanã basin in the Brazilian state of Mato Grosso. The Rio Aripuanã is a right-bank tributary of the Rio Madeira, itself one of the major tributaries of the Amazon. The broader region is characterised by a mix of whitewater and clearwater streams, with many smaller tributaries draining through dense tropical forest.

Specific habitat parameters recorded at the collection site are not widely published in hobbyist literature. However, small-stream tributaries in this region of the Amazon basin typically feature soft, acidic water with low mineral content, moderate to low flow, and substrates composed of sand, leaf litter, and submerged wood. The water is often tannin-stained to varying degrees by decaying plant material. Temperatures in these lowland tropical streams generally fall in the range of 24 – 28 °C (75 – 82 °F), with pH values that can be quite low, often between 4.5 and 6.5.

The dense canopy above many of these small forest streams creates subdued lighting conditions, and the substrate is frequently carpeted with fallen leaves and branches. This kind of environment supports large populations of tiny invertebrates and insect larvae, which form the dietary base for small characins like H. myrmex.

Tank size and setup

Given its tiny adult size, the fire ant tetra does not require a large aquarium, but a minimum volume of around 45 litres (approximately 10 UK gallons) is advisable for a group. This provides enough swimming space and, importantly, enough water volume to maintain stable water chemistry, which is crucial for a species that requires soft, acidic conditions.

The aquascape should aim to replicate the shaded, leaf-litter-rich environment of Amazonian forest streams. A dark, fine-grained substrate such as sand is ideal. Generous quantities of dried leaf litter (Indian almond leaves, oak leaves, or beech leaves) will stain the water with tannins, help to lower and buffer pH naturally, and provide surfaces for microbial biofilms that the fish can graze on. Pieces of driftwood and bogwood further contribute to the tannin-rich environment and provide visual barriers and hiding places.

Live plants are not strictly necessary to replicate the natural habitat, which tends to be dimly lit with relatively sparse aquatic vegetation. However, species tolerant of low light and soft, acidic water work well. Java fern (Microsorum pteropus), various Cryptocoryne species, and mosses such as Java moss can be attached to hardscape. Floating plants are particularly useful for diffusing overhead light, creating the subdued conditions under which these fish tend to show their best colour and most confident behaviour.

The tank should have a secure, tightly fitting lid. Very small tetras are capable jumpers when startled, and evaporative heat loss from an open-topped tank can make temperature management more difficult.

Water parameters

Maintaining appropriate water chemistry is arguably the single most important aspect of keeping Hyphessobrycon myrmex successfully. The species originates from soft, acidic waters, and while precise field measurements from the type locality are not widely available, the following ranges are considered appropriate based on the habitat type and what is known for closely related species.

The low nitrate target of below 10 ppm reflects the fact that this is a wild-caught, soft-water species from a relatively pristine environment. These fish are likely to be more sensitive to dissolved pollutants than hardier, commercially bred tetras. RO (reverse osmosis) or very soft tap water, remineralised minimally to the desired GH, is strongly recommended for UK aquarists, whose mains supply typically far exceeds the hardness range this species requires.

Consistency is at least as important as hitting an exact number. Sudden shifts in pH or hardness can be extremely stressful for small, delicate species. Allow any water changes to match the tank’s existing parameters as closely as possible, and avoid large, abrupt changes.

Filtration and equipment

Filtration should be efficient but gentle. A small sponge filter or an air-driven matten filter is well suited to a nano setup for this species, providing biological filtration without generating strong currents. If using a hang-on-back or small canister filter, ensure the inlet is covered with a fine sponge pre-filter to prevent these tiny fish from being drawn in, and baffle the outlet to reduce flow.

A reliable heater rated for the tank’s volume is essential to maintain the tropical temperature range. In smaller tanks, a heater with a built-in thermostat and a separate thermometer for verification is advisable, as temperature swings in small water volumes can be rapid and dangerous.

Lighting should be subdued. If growing live plants, a low to moderate intensity LED unit will suffice, and floating plants can be used to shade the water column. The fish will be more confident and display better colour under dim lighting. Avoid intense, unshaded overhead lights.

An air pump connected to the sponge filter will provide gentle surface agitation for gas exchange. In a heavily planted or leaf-litter-rich tank with a low fish load, additional aeration is unlikely to be necessary.

Diet and feeding

There is very little published data on the specific diet of Hyphessobrycon myrmex in the wild, though small Hyphessobrycon species are generally micro-predators and opportunistic omnivores, feeding on tiny invertebrates, insect larvae, and organic detritus in their natural environment.

In the aquarium, the key consideration is food size. At around 2 cm SL, this fish has a very small mouth, and all foods offered should be appropriately tiny. Finely crushed high-quality flake food or micro-granules can form a staple, but the diet should be supplemented regularly with small live or frozen foods. Baby brine shrimp (Artemia nauplii), micro-worms, grindal worms, and Daphnia are all excellent choices. Frozen cyclops and finely chopped frozen bloodworm are also suitable.

Feeding small amounts two to three times daily, rather than a single large feed, tends to work well for tiny species. This mimics their natural foraging pattern and reduces the risk of uneaten food fouling the water. In a mature, leaf-litter-rich aquarium, the fish will also graze on the microbial biofilm that develops on decomposing leaves, supplementing their diet between formal feedings.

Behaviour and temperament

Like most small Hyphessobrycon species, the fire ant tetra is a shoaling fish and should be kept in a group. A minimum of eight to ten individuals is recommended; larger groups of fifteen or more will produce more natural behaviour and reduce stress. In too-small a group, these fish tend to be shy, spending much of their time hidden and failing to display their full colouration.

Within the group, males may display to one another, flaring fins and intensifying their colour. These interactions are typically harmless and are part of the species’ normal social behaviour. There are no reports of serious aggression in this species.

The fire ant tetra occupies the middle and lower levels of the water column in the aquarium, often hovering among plant stems, leaf litter, or near driftwood. It is a peaceful, somewhat timid fish that can be easily intimidated by larger or more boisterous tank mates. Providing plenty of cover and keeping the lighting subdued will encourage the fish to spend more time in the open.

Tank mates

The fire ant tetra’s small size and gentle temperament mean that tank mate selection must be approached carefully. Only similarly sized, peaceful species that share its preference for soft, acidic water should be considered. Any fish large enough to view a 2 cm tetra as food is obviously unsuitable. Even moderately active mid-water swimmers can outcompete or intimidate this species at feeding time.

Good tank mates

• Ember tetra, a similarly tiny, peaceful tetra suited to soft, acidic water
• Green neon tetra, a small, undemanding shoaler that thrives in the same water conditions
• Celestial pearl danio, a diminutive, calm species that does well in planted nano tanks
• Pygmy corydoras, a tiny bottom-dweller that shares a preference for soft water and gentle flow
• Dwarf pencilfish, another small, peaceful species from similar habitats
• Least rasbora, an extremely small, placid fish suitable for the same nano setups
• Chocolate gourami, a quiet, soft-water species that occupies different levels of the tank
• Otocinclus, a small, peaceful algae grazer that will not bother tiny tetras
• Clown killifish, a surface-dwelling nano species that complements the fire ant tetra’s mid-level swimming
• Amano shrimp, a useful invertebrate that is too large to be eaten and will help with tank maintenance

Fish to avoid

• Angelfish, large enough to eat fire ant tetras and prefer calmer setups where tiny fish may become prey
• Convict cichlid, aggressive, territorial, and far too large
• Tiger barb, a nippy, boisterous species that will outcompete and harass tiny tetras
• Buenos Aires tetra, too large and active, and may nip at smaller fish
• Oscar, a large predatory cichlid entirely incompatible with nano species
• Red-tail shark, territorial and far too large and aggressive
• Paradise fish, aggressive and a potential predator of very small fish
• Betta, may harass or prey on very small tank mates, and the small tank environment increases risk of conflict
• Common pleco, grows far too large and produces excessive waste for a nano setup
• African butterfly fish, a surface predator that could easily consume a 2 cm tetra

Breeding

Specific breeding reports for Hyphessobrycon myrmex in the aquarium are very limited at the time of writing. The species has not been widely bred in captivity, and detailed accounts of spawning behaviour, egg counts, or fry-rearing for this exact species are not readily available in the published literature or mainstream hobbyist forums.

What can be said with reasonable confidence is that, like other small Hyphessobrycon species, H. myrmex is almost certainly an egg-scattering species. Related tetras typically scatter non-adhesive or semi-adhesive eggs among fine-leaved plants or over leaf litter, with no parental care. The adults will readily consume their own eggs and fry if given the opportunity.

For aquarists wishing to attempt breeding, the general approach used for small Hyphessobrycon species may serve as a starting point. This typically involves conditioning a pair or small group on high-quality live foods, then placing them in a separate, dimly lit breeding tank with very soft, acidic water (pH around 5.0 – 6.0, GH below 2 dGH) and a spawning medium such as fine-leaved plants, spawning mops, or a layer of leaf litter. A mesh or grid at the bottom of the tank can help protect scattered eggs from being eaten. After spawning, the adults are usually removed.

Eggs of related species typically hatch within 24 to 36 hours, and the fry become free-swimming a few days later. First foods would need to be extremely small, likely infusoria or commercially available liquid fry food, progressing to freshly hatched brine shrimp nauplii as the fry grow. However, it must be stressed that these are general guidelines derived from related species, not confirmed protocols for H. myrmex specifically. Anyone who succeeds in breeding this species would make a valuable contribution to the hobby by documenting and sharing their experience.

Common diseases and health

There are no disease conditions unique to Hyphessobrycon myrmex, but as a small, wild-caught species from soft, acidic water, it is likely to be more susceptible to stress-related illness than hardier, commercially bred tetras. The most common health problems in small tetras are generally linked to poor water quality, inappropriate water chemistry, or the stress of unsuitable tank mates. Ich (white spot disease) is perhaps the most frequently encountered ailment and can spread rapidly in a nano tank. Maintaining stable water parameters, avoiding sudden temperature drops, and quarantining new arrivals are the best preventative measures.

Bacterial infections, including fin rot and columnaris, can occur if water quality deteriorates or if the fish sustains minor injuries. In soft, acidic water, beneficial bacteria colonies in the filter can be slower to establish and more sensitive to disturbance, so careful monitoring of ammonia and nitrite levels is important, particularly in newer setups. Regular, small water changes using properly prepared water matched to the tank’s chemistry are preferable to infrequent large changes that risk shocking the fish.

Internal parasites are a concern with any wild-caught fish. Newly imported fire ant tetras should ideally be quarantined for several weeks before being introduced to an established display tank. During quarantine, observe the fish carefully for signs of weight loss, lethargy, abnormal faeces, or any external lesions. If treatment is required, note that many medications are dosed for larger fish and larger water volumes; small species in small tanks can be especially sensitive to overdosing. Always follow the manufacturer’s instructions and, where possible, seek advice from experienced keepers of wild-caught nano species.

Frequently asked questions

How many fire ant tetras should I keep together?

A minimum of eight to ten is recommended, and a group of fifteen or more is preferable. Like most small shoaling tetras, H. myrmex is more confident and displays better colour and more natural behaviour in a larger group.

Is the fire ant tetra suitable for a beginner?

Not ideally. Its requirement for soft, acidic water, its sensitivity to fluctuating water parameters, and its limited availability make it better suited to intermediate or experienced fishkeepers. Beginners looking for a small, colourful tetra might find the ember tetra a more forgiving starting point.

Can I keep fire ant tetras in hard, alkaline tap water?

This is not recommended. The species originates from very soft, acidic habitats. Most UK tap water is significantly harder and more alkaline than what this fish requires. Using RO water, remineralised to a low GH, is the most reliable approach.

Where can I buy fire ant tetras in the UK?

This species is only sporadically available. Specialist importers and online retailers dealing in wild-caught or rare South American species are the most likely sources. It is rarely, if ever, stocked by mainstream high-street aquatic shops. Joining online forums and social media groups dedicated to rare tetras or South American fish can help you find suppliers.

Will fire ant tetras eat shrimp?

Adults are unlikely to threaten adult dwarf shrimp such as cherry shrimp or Amano shrimp. However, as with most small fish, very tiny shrimplets may occasionally be eaten. If breeding shrimp is a priority, providing dense plant cover and leaf litter will improve shrimplet survival rates.

How long do fire ant tetras live?

The specific lifespan of H. myrmex in captivity has not been well documented. Based on similar small Hyphessobrycon species, a lifespan of three to five years in good conditions is a reasonable expectation, but this should be treated as an estimate rather than a confirmed figure.

Do fire ant tetras need a heater?

Yes. This is a tropical species requiring water temperatures in the range of 24 – 28 °C (75 – 82 °F). UK room temperatures are generally too low and too variable to maintain this range without a heater, particularly in smaller tanks.

Related guides

• Ember tetra
• Green neon tetra
• Cardinal tetra
• Neon tetra
• Pygmy corydoras
• Dwarf pencilfish
• Celestial pearl danio
• Clown killifish