Pterophyllum scalare (Lichtenstein, 1823) - freshwater angelfish from the Rio Negro drainage basin of northern Brazil (captives, Newport Aquarium, Newport, Kentucky, USA).

This is not the “angelfish” that most people have heard about. Most angelfish (or angels) are marine fish related to & in the same family as the butterfly fish (Family Chaetodontidae). However, the freshwater angelfish shown here is somewhat similar to the overall body form of marine angelfish (csmp.plongee.free.fr/photos/bio/divers/pomacanthus_arcuat...).

This is Pterophyllum scalare, a cichlid fish (Family Cichlidae). Cichlids are quite variable in body form, but Pterophyllum is unusual even for a cichlid. Garden-variety fish have an elongated, fusiform body (for example, tuna - media.oregonlive.com/opinion_impact/photo/bluefintunajpg-...). Pterophyllum has a laterally compressed and anteriorly-posteriorly truncated body. Marine angelfish also have laterally compressed bodies, but are less truncated. The body form of Pterophyllum is often seen in fish inhabiting low-energy, freshwater settings having moderately thick aquatic vegetation.

Classification: Animalia, Chordata, Vertebrata, Osteichthyes, Actinopterygii, Teleostei, Perciformes, Labroidei, Cichlidae