Polycentridae

{{Short description|Family of fishes}}

{{Automatic taxobox

| image = Monocirrhus polyacanthus.jpg

| image_caption = Monocirrhus polyacanthus

| taxon = Polycentridae

| authority = T. N. Gill, 1858

| subdivision_ranks = Genera

| subdivision_ref = {{cite journal | author = Betancur-Rodriguez|display-authors=etal| title = Phylogenetic Classification of Bony Fishes Version 4 | url= | journal=BMC Evolutionary Biology | volume=17 | issue=1 |date=2017 | doi=10.1186/s12862-017-0958-3 | pmid=28683774 | pmc=5501477 | page=162 |doi-access=free }}

| subdivision = * Afronandus Meinken, 1955

• Monocirrhus Heckel 1840
• Polycentropsis Boulenger, 1901
• Polycentrus Müller & Troschel 1848

}}

Leaffishes are small fishes of the family Polycentridae. They consist of four genera found in fresh and brackish water in South America and Africa. The African species were formerly placed in the family Nandidae (otherwise found only in Asia), but recent taxonomic studies have affirmed their relationship to the South American species.Collins, R.A., R. Britz, and L. Ruber (2015). Phylogenetic systematics of leaffishes (Teleostei: Polycentridae, Nandidae). J Zoolog Syst Evol Res 53(4). {{doi|10.1111/jzs.12103}} Their taxonomic placement was previously debated,{{cite book |author1=J. S. Nelson |url=https://sites.google.com/site/fotw5th/ |title=Fishes of the World |author2=T. C. Grande |author3=M. V. H. Wilson |publisher=Wiley |year=2016 |isbn=978-1-118-34233-6 |edition=5th |pages=752}} but they are now generally placed in the order Cichliformes.{{Cite web |last=Fricke |first=R. |last2=Eschmeyer |first2=W. N. |last3=Van der Laan |first3=R. |date=2025 |title=ESCHMEYER'S CATALOG OF FISHES: CLASSIFICATION |url=https://www.calacademy.org/eschmeyers-catalog-of-fishes-classification |access-date=2025-02-10 |website=California Academy of Sciences |language=en}}

All of these fishes are highly specialized ambush predators that resemble leaves, down to the point that their swimming style resembles a drifting leaf (thus the common name leaf fish); when a prey animal - such as an aquatic insect or smaller fish - comes within range, the fish attacks, swallowing the prey potentially within a quarter of a second. To aid in this lifestyle, all members of the family have large heads, cryptic colors, and very large protractile mouths capable of taking prey items nearly as large as they are. These intriguing behaviors have given the family a niche in the aquarium hobby; however, none of these species are easy to maintain in aquariums, requiring very clean, soft, acidic water and copious amounts of live foods.