Care guide · Freshwater · fish

Redhook myleus

Myloplus rubripinnis

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Myloplus rubripinnis, often called the redhook, is a large South American plant-eating fish in the family Serrasalmidae. Older sources commonly use Myleus rubripinnis; the currently accepted combination is Myloplus rubripinnis. Its red anal fin with a dark edge helps distinguish it from silver-dollar Metynnis, with which it can be confused in trade. This is not a small community fish: adult size, shoaling needs and substantial swimming room make it a serious long-term commitment. Ask about feeding and provenance, and arrange the adult aquarium space before making a purchase decision.

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At a glance

Temperature: 23–27 °C
pH: 6.0–7.0
GH: 0–10 °dGH
Aquarium length: At least 180 cm
Minimum aquarium volume: At least 260 L
Adult size: At least 25 cm
Group size: At least 5 individuals
Temperament: Peaceful

About this species

Seriously Fish reports 250 mm standard length. FishBase records up to 415 mm total length. These are different measurements: standard length ends at the tail base, while total length includes the caudal fin. They cannot be compared directly, but together they show that the fish can become very large. Plan around the largest reported specimens rather than the juvenile size commonly seen for sale.

Natural habitat

Specialist sources report the species across much of northern South America, including the Amazon and Orinoco systems and rivers of the Guiana Shield. It is often found in slower river sections with overhanging or marginal vegetation. This habitat can inform the layout, but local conditions vary. Do not use it to invent water parameters or assume that water movement should be absent.

Aquarium and layout

For an adult group, Seriously Fish recommends a 180 × 38 cm footprint and about 260 litres at the stated height. This is a source-reported minimum; FishBase gives a total length up to 41.5 cm, so large adults may need more room. Keep at least five together, provide open swimming space and fit a strong, secure cover. Before buying, make sure you can provide a suitable aquarium for the long term.

Water conditions

The specialist aquarium guide gives 23–27°C, pH 6.0–7.0 and GH 0–10 dGH. FishBase reports broader environmental values, which are not specific aquarium targets. Aim for stable, well-maintained freshwater. Use reliable filtration and regular water changes; avoid rapid changes during transport or maintenance. Measure your own water and acclimate fish gradually.

Behaviour and group size

Keep this active plant-eater in a group of at least five. It is generally described as peaceful with larger calm companions, but much smaller fish may be eaten. Choose robust tankmates that reach a suitable adult size. The red, dark-edged anal fin is a useful identification feature. A government screening report notes powerful teeth; work carefully during maintenance and keep fingers away from the mouth.

Feeding

The redhook feeds mainly on plant material, including leaves of submerged and marginal plants. Make suitable vegetables and complete vegetable foods, such as spirulina- or algae-based products, the foundation of its diet. It may accept other aquarium foods, but animal foods should not displace plant matter. Spread food so all group members can feed and remove leftovers to protect water quality.

Breeding

Seriously Fish reports that breeding has not been achieved in the aquarium hobby and provides no reliable home breeding method. This guide therefore avoids claiming a fixed trigger, egg count or fry-rearing recipe. Maintain a suitable group and stable conditions, but do not buy the species expecting easy or assured breeding. For an adult fish, sufficient space and safe handling matter more than an unverified breeding plan.

Sources & review

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

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