Breuseghem's Moon Tetra (Bathyaethiops breuseghemi)

Meet Breuseghem's Moon Tetra

Breuseghem's Moon Tetra is a rare African tetra from the Kasai river system in the south of the Congo basin. It is a slim, silvery fish of up to 7 cm with clear fins and a dark spot at the root of the tail, and in a settled group some males show a flash of orangey-red on the dorsal fin. Practical Fishkeeping describes it as sporadically available for many years but far from a common sight, so a group of these is something most visitors to your tank will not have seen before.

Its scientific name is Bathyaethiops breuseghemi. Max Poll first described it in 1945 as Micralestes breuseghemi, and it was later placed in Phenacogrammus, the genus of the Congo tetra, before settling in Bathyaethiops, the moon tetras. You may also see it sold as the Breuseghemi Moon Tetra, Breuseghem's tetra or the rectangle-spot moon tetra, the English name used by FishBase.

Read the names on the label

Tell it apart from the African moon tetra

Practical Fishkeeping notes that African exporters sometimes ship this fish as the African moon tetra, B. caudomaculatus, and Wikipedia also mentions the mix-up. The difference it gives is the dark spot on the tail root: roughly circular in B. breuseghemi, much more oval in B. caudomaculatus. The African moon tetra also grows larger, to 8 cm according to FishBase. The sources do not quite agree on the spot: FishBase's English name speaks of a rectangle, while Practical Fishkeeping calls it roughly circular, so the shape may vary between fish. The genus has six species, listed on Wikipedia, and Moritz and Schliewen published a key to all of them in Zootaxa in 2016.

Check what one purchase brings

One purchase quantity supplies one live Breuseghem's Moon Tetra. The fish are not sexed at sale. Our photographs show the slim, silvery body and clear fins of the species; colour and markings vary between individuals and are often faint for the first days after a journey.

Plan the group before you order

• Group size: Practical Fishkeeping says this fish seems happiest and looks best in a large group in a spacious tank. OATA's minimum for any tetra is five; we suggest eight or more.
• Sexes: a larger group is the best way to get both, since males show colour only when mature and settled.
• Rarity: if you collect unusual fish, our rare and collector fish page lists others like it.
• Arrival: read our live delivery information and order for a day when you are at home.

Plan a spacious tank for an active group

FishBase describes the species as pelagic, an open-water swimmer, and it reaches 7 cm. Give the group length to swim and a calm, well-planted setting.

Use a three-step space check

1. Start at 80 litres. OATA gives 80 litres or more for tetras over 5 cm.
2. Add length. For a group of eight or more we suggest a tank about 100 cm long, in line with Practical Fishkeeping's advice to give them a spacious tank.
3. Check the total. Add every fish to our stocking calculator before ordering.

Build an African biotope

Practical Fishkeeping suggests a biotope set-up: a sandy floor, bogwood, peaty water and African plants such as Bolbitis and Anubias. Both plants grow well in shade and attach to wood, so they stay put while the fish swim around them. A few floating plants add the shade that moon tetras seek in the wild, where Wikipedia describes the African moon tetra living around underwater structures and below floating plants.

Divide the footprint by function

You will find shade-tolerant species among our aquarium plants.

Set water values within the species range

The two main sources broadly agree. Practical Fishkeeping gives pH 6.0–7.0, says soft and acidic water is preferable and the temperature should be in the mid 20s °C, and adds that the fish can adapt to harder, more alkaline water. FishBase gives a little more detail.

Compare the published values

Many UK tap waters in softer areas, such as Scotland, Wales and the north-west of England, will reach this range with a conditioner alone. In hard-water areas, blend tap water with reverse osmosis water and keep the blend the same each week. Our water chemistry guide explains the tests, and the water matcher shows which fish share these values. Ammonia and nitrite must read zero; OATA advises keeping nitrate no more than 20 mg/l above your tap water.

Keep filtration and maintenance steady

Practical Fishkeeping warns that, like many African alestid tetras, this species can be sensitive when first imported, but that once established it is quite simple to keep. Stable, clean water is what carries it through those first weeks, so the filter must be fully matured before the fish arrive.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate and pH at least once a week (OATA).
2. Change at least 25% of the water weekly with conditioned water at the same temperature.
3. Siphon the sand lightly and remove decaying leaves.
4. Rinse filter media in old tank water only.
5. Keep a record so you notice pH drift, which peat and bogwood can cause over time.

Feed small, varied meals

Practical Fishkeeping feeds Breuseghem's Moon Tetra on frozen bloodworm, Daphnia and brine shrimp alongside a good-quality flake. Its relative the African moon tetra is described by Wikipedia as an omnivore that eats small aquatic insects and plant matter.

Build one measured meal

• How often: once a day, as OATA advises, giving only what the group clears within a few minutes.
• The base: a good-quality flake.
• The extras: frozen daphnia, freeze-dried brine shrimp and live bloodworm a few times a week.
• The check: if food lands on the sand uneaten, feed less next time.

Introduce the group gently

OATA's method is to switch off the lights, float the sealed bag for about 10 minutes, then add small amounts of tank water over up to 20 minutes and net the fish across. Practical Fishkeeping warns that after a long journey ammonia rises and pH falls in the bag, so once it is open, move the fish promptly.

Use a first-week checkpoint plan

Practical Fishkeeping advises buying this species only once it has been quarantined for at least a week, and recommends a quarantine or hospital tank whatever the source. Because imported fish can be delicate, a quarantine tank at home is a sensible extra step before adding them to an established community.

Watch the group and act on changes

OATA lists the warning signs: hanging at the surface or lying on the bottom, fast breathing, clamped fins, flicking against objects, white spots, fluffy growths, colour much paler or darker than normal, weight loss and poor appetite.

Pair each observation with an action

Pick African tank mates

Practical Fishkeeping says the species mixes well with most fish, can be a little nippy, and names other African tetras and small West African dwarf cichlids as perhaps the best tank mates. OATA adds the general rule: similar size and temperament, nothing large enough to eat them, and no slow long-finned fish with boisterous tetras.

Screen each tank mate

Our kribensis guide explains how to keep dwarf cichlids alongside tetras. See every fish in our African tetra category, or browse all tetras.

Read the signs of sex and breeding

Practical Fishkeeping notes that some males show an orangey-red marking on the top of the dorsal fin and the area just in front of it, and that this is usually seen only on males. Breeding was not covered in the sources we checked, and OATA notes that tetras rarely breed successfully in a community tank. If you see spawning among the plants, it is worth noting what you saw: reports from keepers help fill the gaps for rarely kept fish.

Answer Breuseghem's Moon Tetra buying questions

What is Breuseghem's Moon Tetra?

It is Bathyaethiops breuseghemi, a peaceful African tetra of about 7 cm from the Kasai system of the Congo basin. It was first described by Poll in 1945 as Micralestes breuseghemi and is also called Breuseghem's tetra and the rectangle-spot moon tetra.

Is it the same fish as the African moon tetra?

No. The African moon tetra is B. caudomaculatus. Practical Fishkeeping says exporters sometimes ship B. breuseghemi under that name, and that the dark spot on the tail root is roughly circular in B. breuseghemi but more oval in B. caudomaculatus.

Why is it called the rectangle-spot moon tetra?

That is the English name FishBase uses. Practical Fishkeeping describes the tail-root spot as roughly circular, so the sources do not agree on its shape; it may vary between fish and populations.

How big does it grow?

Up to 7 cm. FishBase gives 7.0 cm total length and Practical Fishkeeping also says up to 7 cm.

What water does it need?

Practical Fishkeeping prefers soft, acidic water at pH 6.0–7.0 and a temperature in the mid 20s °C, and says it can adapt to harder, more alkaline water. FishBase gives 22–25°C, pH 6.0–7.2 and 6–15°dH.

Is Breuseghem's Moon Tetra nippy?

It mixes well with most fish, but Practical Fishkeeping warns it can be a little nippy. Keep it in a good-sized group and avoid slow fish with long fins.

How do I tell males from females?

Practical Fishkeeping notes that some males show an orangey-red marking on the top of the dorsal fin and the area just in front of it, which is usually missing in females.

How many should I keep?

OATA advises at least five tetras together. Practical Fishkeeping says this species is happiest and looks best in a large group in a spacious tank, so we suggest eight or more.

Is it difficult to keep?

Not once settled. Practical Fishkeeping describes African alestid tetras as sensitive when first imported but quite simple to keep once established, so stable, clean water in the first weeks is the key.

Consult the care references

• Practical Fishkeeping: Breuseghem's tetra, Bathyaethiops breuseghemi — names, origin, size, water values, diet, tank mates, biotope, import sensitivity, sexing and identification.
• FishBase: Bathyaethiops breuseghemi — range, maximum size, temperature, pH, hardness and conservation status.
• FishBase: Bathyaethiops caudomaculatus — the African moon tetra, for comparison.
• Wikipedia: Bathyaethiops — the six species and their common names.
• Wikipedia: African moon tetra — habitat, diet and the trade mix-up with B. breuseghemi.
• Moritz, T. & Schliewen, U. K. (2016). Description of two new Bathyaethiops species from the Congo basin. Zootaxa 4117(4): 476–490 — includes a key to the genus.
• OATA: How to look after tetras and pencilfish — group size, tank size, water, maintenance, feeding, acclimatisation and health signs.
• Practical Fishkeeping: How to acclimatise your new fish or shrimp — transport risks and quarantine.