Flag cichlid

About this species

Mesonauta festivus (Heckel, 1840) is a South American member of the Cichlidae. Its diagonal dark band runs from the snout through the eye towards the dorsal fin, giving rise to the flag-cichlid name. The accepted species occurs in the Amazon and Paraguay basins in Bolivia, Brazil, Paraguay and Peru.

Take care when buying one: Seriously Fish reports that fish sold in aquarium shops as “flag cichlids” are usually M. insignis. A retail label alone is therefore not reliable identification. FishBase lists a maximum published length of 12.1 cm standard length (SL), while Seriously Fish gives 10 cm SL. We use 12.1 cm SL as the cautious planning figure. SL excludes the caudal fin.

Natural habitat

The species is recorded from several drainages in the Amazon and Paraguay basins. The specialist aquarium profile describes it from slower-moving, often vegetated water. FishBase specimen notes show variation among localities: some fish were collected near vegetation over sand or mud, while other records came from sites without abundant aquatic plants. No single observation describes the whole range.

This variation supports an aquarium with quiet areas, cover and open swimming space. A strict biotope reconstruction is unnecessary. The habitat notes do not justify inventing water parameters or claiming that one plant type is essential.

Aquarium and layout

Seriously Fish recommends a minimum base of 120 × 38 cm and gives an approximate volume of 137 litres. Keep both measurements in view: a higher-volume aquarium with a shorter footprint is not automatically suitable. The profile recommends a planted tank with moderate flow, sand, bogwood or branches, and lighting that is not too strong. Leave open swimming space and provide sturdy cover; a breeding pair may defend part of the aquarium.

Use effective biological filtration and avoid sharp changes in temperature or water chemistry. The cited dimensions are the profile’s lower limit, not a guarantee that any community or breeding pair will fit. For multiple large fish, allow more room according to adult size and territorial behaviour.

Water conditions

For aquarium care, Seriously Fish recommends 24–28 °C, pH 6.0–8.0 and 0–5 °dGH, with around pH 6.5 suggested. Keep chosen values stable and acclimate fish gradually. There is no need to chase the full range. The source does not provide a dependable KH range, so none is stated here.

FishBase lists field records including 25–34 °C and pH 6–8. These are ecological observations, not alternative aquarium targets. Use the explicit aquarium recommendations for routine care. Check ammonia and nitrite in a new aquarium and maintain the filter without unnecessarily disrupting its biological function.

Behaviour and group size

The specialist profile describes Mesonauta festivus as peaceful but more aggressive when breeding. Parents may defend a stone or other spawning area. The profile mentions possible tankmates only as broad groups, such as peaceful cichlids and community fish; it does not assess specific species combinations. We therefore do not link named companions here. Matching pH or temperature alone does not prove that a pairing is safe.

Before combining fish, assess adult size, temperament, swimming zone, social needs, territory and available floor space. Also check identity at purchase: the source says many fish offered as flag cichlids are actually M. insignis. A misidentified fish may not match the care and compatibility information for this species.

Feeding

Mesonauta festivus is an omnivore and, according to Seriously Fish, accepts most prepared foods. Vary a suitable complete food with animal supplements such as bloodworm and brine shrimp, plus some vegetable matter. The profile mentions algae wafers as a possible food type, but this is not an assessment of a particular product or brand.

No item in the existing central product catalogue has been confirmed with both an approved match for this species and a current usable offer. Therefore no product card is shown. Choose food by its actual ingredients and pellet size, not a title such as “cichlid food” alone. Feed portions that are eaten and remove leftovers.

Breeding

This species lays eggs on a flat stone or similar surface. Seriously Fish describes the female laying the eggs and the male fertilising them; both parents guard the clutch. The profile reports that more than 200 eggs may be laid. The eggs hatch after roughly two to three days, and the larvae are moved to a pit. Free swimming is reported around another three to four days later.

These timings are approximate source observations, not a guaranteed schedule. Breeding fish may defend territory and can be easily startled, sometimes eating eggs or fry. A quiet location and minimal disturbance are advised. The profile lists newly hatched brine shrimp and powdered fry food for young fish. Plan space for the parents and offspring in advance.

For forming a breeding pair, the specialist MARE 2000 profile advises raising five to seven juveniles together because sex is difficult to determine beforehand. This is a pair-formation method, not an established minimum for every adult group or aquarium. Once formed, a pair needs space during breeding.