Wikipedia
Nandidae
Nandidae, the Asian leaffishes, are small freshwater fishes mostly native to south Asia, though with two species confined to Africa.
These fish usually have small heads, coloration that appears to have evolved to resemble leaves, and very large protractile mouths. Those features, along with their peculiar movements (seemingly intended to resemble a leaf innocently moving through the water) help them to catch fairly large prey compared to their body size, including small fish, aquatic insects, and other invertebrates. They tend to stay in one place and wait for prey; they are "lie-in-wait" predators.
Their odd, leaf-like appearance and unusual behavior make them interesting to aquarium hobbyists.