Taxonomy & naming
Heckel described Monocirrhus polyacanthus in 1840 from Marabitanos, Brazil. It belongs to the Polycentridae, the leaffishes, a family with members in South America and Africa. It is the only Monocirrhus in the family.
Morphology
A compressed, leaf-shaped fish with a pointed snout and a short chin barbel, and a body colour that ranges from yellow to brown. FishBase gives a maximum of 3 in SL. It drifts head-down in the water to resemble a leaf.
Habitat
FishBase records it from the Amazon basin in Peru, Brazil, Bolivia, Colombia and Venezuela, freshwater and benthopelagic. The cached record gives 72–77 °F, pH 5 to 6 and hardness 5 to 8 dH.
Feeding
FishBase records that it feeds on fish. It ambushes small fishes and shrimps and lunges with its extendable mouth. In captivity it takes live foods and many specimens refuse dead foods.
Mating
Courtship has not been described in the sources available to the atlas.
Breeding
FishBase gives up to 300 eggs. Leaffishes are known to lay eggs on a leaf or hard surface, where the male guards them.
In the aquarium
Keep it in a quiet tank with leaf litter, wood and floating plants, in soft acidic water, and only with fish too large to be eaten. Feed live foods such as guppies or ghost shrimp; start with captive-bred feeders.
Conservation
The IUCN Red List classes Monocirrhus polyacanthus as Least Concern (assessed 4 November 2020). It is widespread in the Amazon basin.