Megasema Eartheater (Geophagus megasema)

Choose Geophagus megasema, the big-spotted eartheater of the upper Madeira

Geophagus megasema is a large, peaceful sand-sifting cichlid from the upper rio Madeira basin, where it is recorded from the Río Mamoré and Río Guaporé drainages of Bolivia and Brazil (in Bolivia the Guaporé is called the Iténez). Johann Heckel described it in 1840 from the Rio Guaporé in Mato Grosso. Its name joins the Greek mega, large, and semeion, a mark, after the big, roundish black spot in the middle of each flank. Our photographs show that spot on an olive-grey body, with blue-spotted fins edged in red-orange.

Seriously Fish calls it very rare in the aquarium hobby: it may never have been available commercially, although private collectors have collected, bred and distributed it. That makes it a fish for the keeper who wants something genuinely unusual, has room for a group of large eartheaters and is prepared to run a big, very clean aquarium.

Check the identification points

Seriously Fish warns that identifying members of the G. surinamensis group is difficult: juveniles of most species look almost identical, and many are sold as G. surinamensis whatever their origin. If you already keep our Surinam Geophagus or Pindare Eartheater, keep G. megasema in a separate aquarium if you plan to breed, so that every fish stays easy to identify.

Know exactly what you receive

One purchase supplies one live Geophagus megasema. The size option is "Standard": the fish is sent at the size currently available, which is a young fish well below the adult size given below. Sex is not chosen or guaranteed. Seriously Fish states that younger fish are impossible to sex accurately by eye.

The photographs show the species, not the individual you will receive. Young fish have softer colours and shorter fins than adults, and any fish looks paler for a few days after a journey.

Decide how many to order

• Five to eight fish: the minimum purchase Seriously Fish recommends. The species is gregarious, juveniles group strongly, and a group forms a visible pecking order.
• Not one or two: in small numbers weaker fish can be bullied by dominant ones, or the group may never settle and stay nervous.
• Buy them together: young fish added at the same time grow up as one group, and pairs form naturally later.

Read our delivery and Live Arrival Guarantee information before ordering, and have the aquarium matured, heated and filtered for the full group before the fish arrive.

Plan a very large aquarium for a group

Seriously Fish gives a maximum of 175 mm standard length, and FishBase records 18.9 cm standard length. Standard length runs from the snout to the base of the tail, so the whole fish is noticeably longer. Mature males tend to be a little larger and longer-finned than females.

For a group of this size, Seriously Fish asks for an aquarium base of at least 180 × 60 cm, about 648 litres. That is more than twice the 300 litres OATA gives as a general minimum for American cichlids over 15 cm. OATA's figure is for larger American cichlids in general, most of which it says do better singly or in pairs, whereas G. megasema needs a group.

Run a three-step space check

1. Measure the base: 180 × 60 cm or more, with the depth front to back as important as the length.
2. Count the group and companions: five to eight eartheaters plus any characins and catfish; our stocking calculator helps you check the total.
3. Calculate the true volume: our tank volume calculator gives the litres you need for sizing filters, heaters and water changes.

An aquarium of this size is heavy; stand it on a floor and cabinet rated for the load, away from radiators, windows and draughts. OATA advises heating all year round and keeping the tank out of direct sunlight.

Lay a wide, soft sand floor

Seriously Fish expects its wild habitat to resemble that of related species: gently sloping margins with soft beds of bare sand or mud near shores or islands, with scattered rocks, submerged tree roots, branches and leaf litter in places. The upper Madeira is spectacularly diverse, with more than 400 freshwater fish species reported. In the aquarium the most essential item is a soft, sandy substrate; gravel or small pebbles can stop the fish feeding, damage the gill filaments and even be swallowed.

Divide the floor by function

Set rocks on the glass before adding sand, and keep plants to tough species in pots or tied to wood. The more open sand you leave, the more natural group feeding you will see.

Keep the water stable above all

Seriously Fish gives 22–30°C, pH 5.5–7.5 and 1–15 dGH, and warns that the species is extremely susceptible to deteriorating water quality and to swings in water chemistry. These ranges are wide; what matters is that your water stays the same week after week. Pick one temperature inside 22–30°C and hold it; a value near the middle leaves a safety margin for a hot summer or a failing heater.

Match your water to the targets

UK tap water ranges from soft in much of Scotland, Wales and north-west England to hard in much of the south and east. Soft and moderately hard supplies usually fall inside 1–15 dGH; in the hardest areas, a blend of tap water and reverse-osmosis water keeps you inside the range. Mix the same blend every time so the chemistry does not swing. Treat all new water with a conditioner, as OATA advises. Our water chemistry guide explains pH, GH and KH and how to test them.

Over-filter with gentle flow

Seriously Fish recommends over-filtering the aquarium with external canister filters, a sump or both, and changing at least 50–70% of the water every week. Without that, it warns, head and lateral line erosion or stunted growth can follow. For a tank of about 648 litres its equipment note suggests two filters rated around 1,295–1,620 litres per hour each, and roughly 175–250 W of heating spread over three heaters. It also advises against high flow rates, so position filter returns to move the surface, not to blast the sand.

Follow a weekly routine

1. Test ammonia, nitrite, nitrate and pH; OATA recommends testing at least once a week.
2. Change 50–70% of the water with conditioned water matched for temperature and hardness.
3. Siphon debris from the top of the sand and around the roots.
4. Clean the fine mechanical media, which catches the particles the fish stir up, in removed tank water, never under the tap.
5. Check that sand has not reached any filter intake or impeller.

Our guide to aquarium filtration explains how to run two canisters or a sump on a large aquarium.

Feed fine foods in small, frequent meals

Geophagus feed by taking mouthfuls of sand and sifting them, then passing the rest out through the gills and mouth; that habit gave the group the name eartheaters. Seriously Fish reports that wild stomach contents are mostly small aquatic and terrestrial invertebrates, seeds, organic detritus and sediment, and that even adults cannot properly swallow larger food. Once settled, the fish rise to take food at feeding time but carry on sifting the rest of the day.

Build one measured meal

• Staple: a variety of high-quality, fine-grade sinking foods, some of them rich in vegetable matter such as spirulina.
• Small frozen foods: bloodworm, brine shrimp and mosquito larvae.
• Homemade option: gelatine-bound mixes of dry food, puréed shellfish, fruit and vegetables, cut into small discs.
• Timing: three to four small portions a day, which Seriously Fish links to the best growth and condition.
• Spread: scatter food over the sand so the whole group can sift, not only the dominant fish.

Siphon any food left on the sand after a few minutes; in a group of large eartheaters, leftovers quickly add to the waste load.

Introduce the group to a mature aquarium

Seriously Fish is clear that this species should never be introduced to a biologically immature aquarium. Before the fish arrive, the filters must be fully matured, ammonia and nitrite must read zero and the temperature must be steady. Use OATA's floating-bag method: lights off, float the sealed bag for about 10 minutes, add small amounts of tank water over up to 20 minutes, then release the fish with as little bag water as possible. Our guide on how to acclimatise new fish covers each step, and our cichlid care guide explains the basics for all cichlids.

Use a first-week checkpoint plan

A nervous group that stays in cover for long periods usually needs more fish, more cover or calmer companions. Gasping, clamped fins or a fish lying on the sand call for an immediate water test.

Choose peaceful companions from soft-water rivers

Unless breeding, Seriously Fish describes this species as surprisingly peaceful: it will not prey on fish larger than a few millimetres, and suitable tank mates are too numerous to list, covering most peaceful species that enjoy the same conditions. It advises avoiding aggressive or territorial bottom-dwelling species and fish that need harder water. It also notes that eartheaters are sometimes kept with freshwater stingrays, usually successfully, though in some tanks the eartheaters have disappeared at night.

Screen each companion

Check every planned mix with our tank mates tool, browse all South American cichlids, the South American cichlid category and our Geophagus range, or look through our rare and collector fish.

Watch for problems early

OATA describes a healthy fish as having clear, bright eyes, undamaged fins, intact scales, no ulcers or bumps, normal swimming and steady breathing; clamped fins, flicking against décor and shimmying are warning signs. In a group, watch the weakest fish as closely as the strongest.

Pair each sign with an action

In big eartheaters most health problems follow a drop in water quality, so test and correct the water before treating.

Breed a biparental mouthbrooder

Seriously Fish describes G. megasema as a substrate-spawning, biparental mouthbrooder that has been bred in aquariums. There is no particular trigger beyond a good diet and large weekly water changes, but patience is needed: the fish can take at least a year to mature.

Set up for a spawning

1. Let pairs form: since young fish cannot be sexed, grow on a group and let pairs choose each other.
2. Watch the courtship: fin flaring, circling, gaping and head jerking; the pair then cleans and defends a flat rock, a piece of driftwood or a patch of the tank floor.
3. Expect mouthbrooding: the female lays rows of eggs that the male fertilises, up to around 200 in all, and she normally takes them into her mouth while he defends the territory.
4. Watch the shared care: once the fry swim freely, at 7–14 days old, both parents may carry them and pass the brood between them; the fry dart back into a parent's mouth when danger threatens and later only at night.
5. Feed the fry: fine powdered dry food, brine shrimp nauplii and microworm as soon as they swim freely.

In a community aquarium, Seriously Fish recommends removing brooding females, because the released fry are easy prey for other fish, including their own kind.

Answer Geophagus megasema buying questions

What is Geophagus megasema?

It is a large, peaceful eartheater cichlid described by Heckel in 1840 from the Rio Guaporé in Mato Grosso, Brazil, and found in the Guaporé and Mamoré drainages of the upper rio Madeira in Brazil and Bolivia. Its name means "large mark", after the big, roundish dark spot in the middle of each flank.

How big does Geophagus megasema grow?

Seriously Fish gives a maximum of 175 mm standard length and FishBase records 18.9 cm standard length; standard length leaves out the tail, so the whole fish is longer. Males tend to be a little larger than females, with longer fins.

What size aquarium does it need?

A big one. Seriously Fish asks for a base of at least 180 × 60 cm, about 648 litres, because it should be kept as a group of five to eight. That is well above OATA's general 300 litres for larger American cichlids.

Can I keep just one?

It is a gregarious fish that lives in loose groups in the wild, and Seriously Fish recommends five to eight as the minimum purchase. Kept in smaller numbers, weaker fish can be bullied by dominant ones, or the group may fail to settle and stay nervous.

What water conditions does it need?

Seriously Fish gives 22–30°C, pH 5.5–7.5 and 1–15 dGH. More important than the exact figures is stability: it is extremely sensitive to falling water quality and to swings in water chemistry, so over-filter and change 50–70% of the water every week.

Is Geophagus megasema peaceful?

Yes, unless breeding. Seriously Fish describes it as surprisingly peaceful and says it will not prey on fish larger than a few millimetres. Avoid aggressive or territorial bottom dwellers and fish that need harder water.

How does it breed?

It is a biparental mouthbrooder that spawns on a hard surface. The female usually takes up the eggs, up to around 200, and both parents later share brood care, carrying the fry in their mouths until they are independent.

How many fish come with one purchase?

One live fish of the standard size currently available, normally a young fish well below adult size. Sex is not chosen or guaranteed; young fish cannot be sexed by eye.

Consult the care references

• Seriously Fish: Geophagus megasema — names, upper Madeira distribution and habitat, size, aquarium base, water values, maintenance, diet, group behaviour, sexing, biparental mouthbrooding and the G. surinamensis group.
• FishBase: Geophagus megasema — maximum recorded length, distribution and IUCN status.
• OATA: How to look after American cichlids — UK group-level guidance for American cichlids: water values, tank sizes, substrate, heating, acclimatisation, health checks and weekly maintenance.
• Tropical Fish Co delivery policy — current dispatch days and Live Arrival Guarantee terms.