Pterophyllum leopoldi can be differentiated from other members of the genus by the presence of up to 11 vertical stripes on the body, though often only the 3 largest, boldest stripes can be seen. This species also shows a dark patch over the operculum.

In adult specimens, a red/maroon hue over the back and fins is characteristic of the species, leading some to believe the most colourful natural form Angelfish.

The name-sake roman nose possessed by the fish is also very distinctive and used as a meristic feature.

Apistogramma commbrae and other members of the commbrae complex can be distinguished from congeners by the conspicuous double caudal peduncle spot. This species may also be polymorphic, with some males exhibiting red and blue markings on the cheeks and a yellow gular region.

An efficient, largely piscivorous, predator with highly protrusible mouthparts. In the aquarium, juveniles can be offered chironomid larvae (bloodworm), small earthworms, chopped prawn, and suchlike, while adults will accept strips of fish flesh, whole prawns, mussels, live river shrimp, larger earthworms, etc. Older individuals do not require feeding on a daily basis, with 2-3 times per week sufficient.

The massive decline in wild populations, hypothesised to be in excess of 90% since the mid-1980s, is thought to have been caused by a variety of factors, including habitat alteration due to construction of dams and other infrastructure, removal of riparian vegetation, and urban pollution, plus over fishing for both human consumption and the aquarium trade.

Apparently restricted to the southern portion of New Guinea, between the Lorentz River in Papua province, Indonesia, and Kikori River in Gulf province, Papua New Guinea. The majority of records pertain to the lower Fly River basin in Western province, southwestern Papua New Guinea.

Known from the lower Mekong River basin in Laos, Thailand, Cambodia, and Vietnam, plus tributaries of the Chao Phraya watershed in central Thailand, and drainages between the Chao Phraya and Mekong in eastern Thailand.

Type locality is ‘Nam-Mun at Korat, 135 miles northeast of Bangkok, Thailand’.

In 1996 the species was known from five localities in Hong Kong, but at least one of these has been destroyed and it is now known only from Tai Po and Sai Kung districts. Additional populations have subsequently been discovered in Guangdong and Fujian provinces on the southern Chinese mainland.

Type locality is ‘China: Hong Kong: Tai Po: Sha Lo Tung’.

This species is frequently mistaken for the similar-looking congener M. spechti Schreitmüller 1936, which is easily-identified by the absence of reddish pigmentation in the dorsal, anal, and caudal fins. There has been some debate as to whether these two represent the same taxon, however, with Winstanley and Clements (2008) proposing that M. erythropterus be considered a synonym of M. spechti because they were unable to separate the two species by morphological characters, and specimens with red pigmentation on the unpaired fins were coll…