Care guide · Freshwater · fish

Reed tetra

Hyphessobrycon elachys

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The reed tetra (Hyphessobrycon elachys), also traded as the veilfin tetra, is a very small South American characin. It comes from the Paraguay basin and is encountered less often in the aquarium trade than familiar tetras. Specialist species data lists a maximum of about 2 cm standard length; an older aquarium article reports 3–4 cm without specifying the same measurement basis. Treat it as a miniature fish: provide a calm, mature aquarium, appropriately fine food, and tankmates that will not chase it or see it as prey. One detailed species profile recommends at least 80 cm tank length and 80 litres for a group of at least ten. This is a conservative husbandry recommendation, not a universal biological threshold.

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At a glance

Temperature: 24–27 °C
pH: 6.0–7.2
GH: Up to 15 °dGH
Aquarium length: At least 80 cm
Minimum aquarium volume: At least 80 L
Adult size: Up to 2 cm
Group size: At least 10 individuals
Temperament: Peaceful

About this species

Hyphessobrycon elachys was described by Weitzman in 1984 and is treated as valid by FishBase and ITIS. It is generally placed among the American tetras; recent classifications use Acestrorhamphidae, while older aquarium literature often says Characidae. Common names are not fully standardised. Reed tetra is used here as the English name; veilfin tetra is a trade name.

It is a small, slender fish with a conspicuous dark mark near the base of the tail. Mature males may develop longer dorsal and pelvic fins. Appearance varies with sex, condition and lighting. Do not confuse it with the similar H. heliacus, which has a golden appearance and differs in fin and flank characters.

FishBase reports a maximum of 2 cm standard length (SL). An older aquarium article gives about 3–4 cm but does not state its measurement basis. These values are not directly comparable. We therefore retain the standardised SL value as the cited data point and recommend extra caution when selecting tankmates.

Natural habitat

The species is recorded from the Paraguay basin and, in specialist literature, also the Mamoré and Guaporé basins. FishBase currently shows Paraguay only. FishBase describes it as a freshwater, benthopelagic fish. Habitat accounts point to slow-flowing waters, side channels and seasonally flooded areas. Local conditions vary between wet and dry seasons, so one water colour or chemistry does not represent the entire range.

Do not imitate an extreme biotope based only on a regional label. Provide stable water, gentle flow, sheltered areas and open swimming space. Fine-leaved plants and floating cover can offer refuge, but leave clear areas where fish can find food. Leaf litter and organic structure do not replace maintenance or water testing.

In nature the species may occur in mixed shoals with small tetras. A field observation is not a universal aquarium compatibility guarantee. Available species sources do not support specific plant prescriptions, exact current speeds or fixed site-by-site water parameters.

Aquarium and layout

Choose a mature aquarium with a gentle filter outlet and fine cover along parts of the sides and back. Leave open water as well, so fish can swim and reach food. A dark substrate and subdued light may make them easier to observe, but neither is a proven requirement. Floating plants can be used to soften the light.

This fish is too small to house with species that could swallow it, actively chase it or exclude it from food. Choose only very peaceful, small tankmates and check that every fish eats. A species aquarium is sensible if the group remains shy. One detailed species profile recommends at least 80 cm length and 80 litres for a group of at least ten. This is a conservative recommendation, not a scientifically established minimum; allow additional space when keeping other species. A longer tank provides more usable swimming space than a tall nano tank of equal volume.

Allow the aquarium to mature before adding fish. Check ammonia and nitrite after setup and whenever problems arise; both should be undetectable in a stable aquarium. Avoid rapid changes in temperature, pH or mineral content. Strong flow is not a substitute for oxygenation or maintenance.

Water conditions

FishBase lists 24–27°C, pH 6.0–7.2 and an upper hardness value of 15°dH for its reported range. It does not provide a lower hardness value. Practical Fishkeeping gives similar guidance of roughly 24–27°C and pH around 6–7.2, noting that gradual acclimation to harder water may be possible. This does not justify abrupt changes from the source water.

Aim for stable, soft to moderately hard conditions within the documented limits. Test tap or source water and ask about the fish’s recent holding conditions. Make changes gradually, especially after transport or a move. No KH value or salt addition is presented because no dependable species-specific recommendation was found.

Measure temperature with a reliable thermometer and use suitable tests for pH and hardness. Avoid repeated rapid chemical corrections; stability and a functioning biological filter matter more than chasing one ideal number.

Behaviour and group size

Practical Fishkeeping describes the reed tetra as peaceful and suitable for a community aquarium when kept in a small group. Because it is exceptionally small, it may feel insecure with boisterous or much larger fish. A group provides social context, but the reliable sources reviewed do not establish one exact minimum number for every aquarium. Keep a suitable group and monitor hiding, fin damage and unequal feeding.

The species is reported in the water column near lower zones. Provide both planted shelter and open swimming space. Avoid long-finned fish and larger predators; be cautious with bottom-dwellers that compete strongly at feeding time. Quarantine new fish and observe behaviour for several days.

Sex differences are subtle. Mature males may show elongated dorsal and pelvic fins; a fuller abdomen can suggest a mature female, but is not reliable by itself. Do not select a breeding group on a single visual character.

Feeding

The aquarium source reports that the fish accepts dried, frozen and live foods. Because it is so small, offer pieces that can be taken safely. Feed small portions and check that shy individuals actually eat. Remove leftovers before they degrade water quality.

Offer a varied menu with fine dry food and suitably small animal foods. The sources do not support a species-specific feeding schedule or exact daily amount. Adjust portions to what is eaten promptly and prevent larger tankmates from taking all the food. Do not rely on algae or plants as a required staple; the available species data does not confirm that.

New arrivals may feed cautiously after transport. Offer suitable small food without repeatedly disturbing the aquarium. Persistent refusal, rapid breathing or weight loss calls for checks of water quality, quarantine and health.

Breeding

The reliable aquarium sources reviewed do not provide a sufficiently complete, repeatable breeding account for this species. No exact breeding recipe is therefore included. Sexes may differ somewhat in fin shape and body profile, but appearance alone does not guarantee a pair or successful spawning.

If you investigate breeding, use a separate, fully matured aquarium and keep adults and young apart when predation is possible. Do not change water conditions abruptly; monitor water quality and feeding daily. Species-specific data on eggs, hatch time, larval food and rearing are not confirmed well enough to publish fixed numbers or timelines.

Record observations and compare them with specialist literature before treating them as general care rules. An occasional fry in a community aquarium does not prove that conditions were optimal.

Sources & review

This care guide draws on several specialist sources and was last checked on 16 October 2026.

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