Green's Moon Tetra (Bathyaethiops greeni)

Meet Green's Moon Tetra

Green's Moon Tetra, also sold as the Green Back Moon Tetra, is a small, peaceful African tetra from the forest rivers of the middle Congo basin. It is a compact, silvery-gold fish with large eyes and clear fins, and a group moving through plants in soft light has the gentle shimmer that gives the moon tetras their name. Few UK shops ever list it, which makes it a rewarding fish for anyone building an African biotope or a calm planted community.

Its scientific name is Bathyaethiops greeni, described by Fowler in 1949. According to Wikipedia, it is the type species of the genus, which means the genus name is anchored to it. The species name greeni is a person's name in Latin form, which is why FishBase gives the English name as Green's moon tetra; "Green Back" is a shop name rather than a description of colour.

Read the names on the label

Know the moon tetra family

Wikipedia lists six species in the genus: B. atercrinis, B. baka, B. breuseghemi, B. caudomaculatus, B. flammeus and B. greeni. Two of them were described as recently as 2016 by Moritz and Schliewen in a peer-reviewed paper in Zootaxa, which also gives a key to all species: a dwarf species, B. baka, and the red-back moon tetra, B. flammeus, which has a spot in front of the dorsal fin that is bright red in life. Do not confuse that red-back fish with this one. The best-known member, the African moon tetra (B. caudomaculatus), is described as deep-bodied and golden with a large black spot at the base of the tail and a small red spot under the dorsal fin.

Check what one purchase brings

One purchase quantity supplies one live Green's Moon Tetra. The fish are not sexed at sale. Our photographs show a silvery-gold fish with a round dark shoulder spot, two dark bars and red at the base of the tail; markings and colour vary between individuals and fade for a while after a journey.

Plan the group before you order

• Group size: OATA advises at least five tetras together and says more is better. Wikipedia notes that the African moon tetra does well in large groups, so we suggest eight or more.
• Size: FishBase gives a maximum of 6.0 cm total length, smaller than the African moon tetra (8 cm) and Breuseghem's moon tetra (7 cm).
• Arrival: plan the order for a day when you are home; our delivery information explains how live fish travel.

Plan the aquarium around a midwater shoal

FishBase describes the species as pelagic, which means it lives in open water rather than on the bottom. A group needs a clear swimming area in the middle of the tank with planting around it.

Use a three-step space check

1. Start with OATA's floor. OATA gives 80 litres or more for tetras that grow beyond 5 cm.
2. Add length for the group. For eight or more fish we suggest a tank about 90–100 cm long, which also suits most tank mates. Our article on the best fish for a 100 litre tank shows how to fill a tank of that size.
3. Check the mix. Run your planned fish through the tank mate checker before ordering.

Arrange plants, wood and shade

Wikipedia describes the African moon tetra as living in densely vegetated streams, backwaters and slow rivers, often around underwater structures or below floating plants. Its relatives share that habitat, so the same layout suits Green's Moon Tetra: a well-planted tank with wood, a soft floor and some shade from above.

Divide the footprint by function

Practical Fishkeeping suggests exactly this kind of biotope for the related Breuseghem's tetra: a sandy floor, bogwood, peaty water and African plants such as Bolbitis and Anubias. Browse our aquarium plants for suitable shade-tolerant species.

Set water values for a Congo tetra

FishBase gives only a temperature range for B. greeni, 22–28°C. For pH and hardness we use the values FishBase lists for its two best-known relatives, which come from the same river system, and the general tetra range from OATA.

Compare the published values

That range is wider and harder than many Amazon tetras need, so many UK tap waters will be suitable once conditioned, especially in softer areas such as Scotland, Wales and the north-west of England. In very hard areas, blend tap water with reverse osmosis water to bring the hardness down. 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.

Build filtration and a weekly routine

A matured filter is essential, and the flow should be moderate, with calmer water among the plants. Practical Fishkeeping notes that African alestid tetras can be sensitive when first imported but are quite simple to keep once established, so stable water in the first weeks matters most.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate and pH at least weekly (OATA), and more often in the first month.
2. Change at least 25% of the water each week with conditioned, temperature-matched water.
3. Siphon the floor and remove dead leaves from plants.
4. Clean filter media only in water taken from the tank.
5. Write down the results so you can see slow changes.

Feed small varied meals once a day

Wikipedia describes the African moon tetra as omnivorous, eating small aquatic insects and plant matter. Practical Fishkeeping feeds the related Breuseghem's tetra on frozen bloodworm, Daphnia and brine shrimp alongside a good-quality flake. Green's Moon Tetra can be fed the same way.

Build one measured meal

• How often: once a day, giving only what the group clears within a few minutes (OATA).
• The base: a quality flake or small granule.
• The extras: frozen daphnia, freeze-dried brine shrimp or freeze-dried bloodworm two or three times a week.
• The check: no food should reach the floor uneaten. If it does, feed less.

Introduce the group to a mature aquarium

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 before netting the fish across. Practical Fishkeeping adds that ammonia builds up during a long journey and the pH drops, so after the bag is opened the fish should go in promptly. Our guide to acclimatising new fish covers both steps.

Use a first-week checkpoint plan

Practical Fishkeeping recommends a quarantine or hospital tank whatever the source of your fish, and advises buying the related Breuseghem's tetra only once it has been settled for at least a week.

Watch the group and act on changes

OATA's list of warning signs applies to every tetra: hanging at the surface or sitting on the bottom, fast breathing, clamped fins, flicking against objects, white spots, fluffy growths, a colour much darker or paler than usual, weight loss and poor appetite.

Pair each observation with an action

Build an African or community shoal

Green's Moon Tetra is a peaceful fish that suits a calm community. For the related Breuseghem's tetra, Practical Fishkeeping names other African tetras and small West African dwarf cichlids as the best tank mates, and warns it can be a little nippy. We apply the same advice here, together with OATA's rule to keep tetras with fish of similar size and temperament.

Screen each tank mate

The Congo Tetra is a larger fish that shares the family and the river basin, and a mixed African tetra tank is one of the most attractive ways to keep both. See all our African tetra category fish, or our full range of African and South American tetras.

Read the signs of sex and breeding

The sources we checked do not describe how to sex B. greeni or how it breeds. In the African moon tetra, Wikipedia notes that females are generally deeper-bodied and have a smaller red spot under the dorsal fin; in Breuseghem's tetra, Practical Fishkeeping notes that some males show an orangey-red marking on the dorsal fin and just in front of it. Expect similar differences as your group matures. OATA notes that tetras rarely breed successfully in a community tank.

Answer Green's Moon Tetra buying questions

Is the Green Back Moon Tetra the same as Green's Moon Tetra?

Yes. Both names are used for Bathyaethiops greeni. FishBase lists the English name as Green's moon tetra: greeni is a person's name in Latin form, so it does not describe a green back.

Where does Bathyaethiops greeni come from?

The middle Congo River basin. FishBase records it from the Likouala drainage in the Republic of the Congo and the Ruki and Lake Mai Ndombe drainages in the Democratic Republic of the Congo.

How big does it grow?

FishBase gives a maximum of 6.0 cm total length. That is smaller than its better-known relatives: FishBase gives the African moon tetra 8 cm and Breuseghem's moon tetra 7 cm.

How many should I buy?

OATA advises at least five tetras together. Moon tetras do best in a larger group, so we suggest eight or more in a tank of at least 80 litres, ideally 90–100 cm long.

What water does it need?

FishBase gives 22–28°C. Its close relatives are listed at pH 6.0–7.3 and 5–15°dH, so aim for 23–26°C, pH 6.5–7.2 and soft to medium hardness. Many UK tap waters are close to this after conditioning.

Is it a community fish?

Yes, with calm fish of a similar size: other African tetras, small West African dwarf cichlids and peaceful catfish. A close relative can be a little nippy, so avoid long-finned fish.

How do I tell males from females?

No source we checked describes the sexes of B. greeni. In related moon tetras, males carry more red on or in front of the dorsal fin and females are deeper-bodied, so look for those differences as the fish mature.

Why are my new moon tetras pale and shy?

Practical Fishkeeping notes that African alestid tetras can be sensitive when first imported. Give them a dim, planted tank, stable water and small meals, and colour usually returns within a week or two.

Consult the care references

• FishBase: Bathyaethiops greeni, Green's moon tetra — author, range, maximum size, temperature and conservation status.
• Wikipedia: Bathyaethiops — the six species, type species and countries.
• Wikipedia: African moon tetra — appearance, habitat, diet, behaviour and sex differences in the best-known relative.
• FishBase: Bathyaethiops caudomaculatus and FishBase: Bathyaethiops breuseghemi — water values and sizes of the relatives.
• FishBase: Bathyaethiops flammeus — the red-back moon tetra.
• Moritz, T. & Schliewen, U. K. (2016). Description of two new Bathyaethiops species from the Congo basin. Zootaxa 4117(4): 476–490 — the 2016 species and a key to the genus.
• Practical Fishkeeping: Breuseghem's tetra — care, tank mates, biotope and import sensitivity of a close relative.
• OATA: How to look after tetras and pencilfish — group size, tank size, water values, maintenance, feeding and health signs.
• Practical Fishkeeping: How to acclimatise your new fish or shrimp — acclimatisation and quarantine.