| Serrasalmidae Temporal range:Miocene - present | |
|---|---|
 | |
| Serrasalmus manueli | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Superfamily: | Erythrinoidea |
| Family: | Serrasalmidae Bleeker, 1859 |
| Genera[1] | |
Acnodon | |
TheSerrasalmidae (serrasalmids) are a family ofcharaciform fishes, recently[when?] elevated to family status. It includes more than 90 species. The name means "serratedsalmon family", which refers to theserrated keel running along the belly of these fish. Fish classified as Serrasalmidae are also known by these common names:pacu,piranha, andsilver dollar. These common names generally designate differingdental characteristics and feeding habits.[2]
Serrasalmids are medium- to large-sized characiform bony fishes that reach about 1 m (3.3 ft) long, generally characterized by a deep, laterally compressed body with a series of midventral abdominalspines orscutes, and a longdorsal fin (over 16 rays). Most species also possess an anteriorly directed spine just before the dorsal fin extending from a supraneural bone; exceptions include members of the generaColossoma,Piaractus, andMylossoma.[3]
Most serrasalmids have about 60chromosomes, ranging from 54 to 62.Metynnis has 62 chromosomes, as doesCatoprion,Pristobrycon striolatus, andPygopristis.[4]
Serrasalmids inhabit all major and some minorAtlantic river systems inSouth America east of theAndes, but have beenintroduced to other areas.[5] Species range from about10°N latitude south to about35°S latitude.[6]
The diets of the various serrasalmid fishes includeseeds,fruits,leaves, and variousinvertebrate andvertebrate prey, as well as fish flesh,scales, and fins. To emphasize the diversity of diets, authors commonly highlight the fruit- and leaf-eatingpacus and the highly carnivorouspiranhas. Most in the family other than piranhas are primarilyherbivorous. In contrast, piranhas have been long believed to be strictcarnivores.[4] Many species change diets depending on age and resource availability.[4]
The primarily carnivorous piranha group comprises the generaCatoprion,Pristobrycon,Pygocentrus,Pygopristis andSerrasalmus, but based onphylogeny also the mainly herbivorous (although withomnivorous tendencies)Metynnis.[7] The remaining primarily herbivorous species can be divided into two groups based on ecology and, to some extent, phylogeny:Colossoma,Mylossoma andPiaractus are mainly found in relatively slow-moving waters, and feed extensively on fruits, nuts and seeds, playing an important role asseed dispersers.Mylesinus,Myleus,Ossubtus,Tometes andUtiaritichthys are found in fast-flowing sections of rivers, and mainly feed on aquatic plants, especiallyPodostemaceae.[7]Myloplus mostly feed on plant material and some of its species are phylogenetically related with the previous group, but this genus includes species of both slow and fast-flowing waters.[8]
The Serrasalmidae were recently classified as a subfamily of theCharacidae. Their relationship to other characiforms has yet to be determined.[6] Thetaxonomy and systematics of piranhas and their relatives are complicated and much remains unsettled. Consequently, both species identification and phylogenetic placement of manytaxa are problematic.[6]
However, the ongoing classification of these fish is difficult and often contentious, withichthyologists basing ranks according to characteristics that may overlap irregularly (seeCladistics). Ultimately, classifications can be rather arbitrary.[2]
Despite this, the Serrasalmidae are relatively well understood, and agreement is wide on the genera and species included.[3]
The fossil record, particularly for piranhas, is relatively sparse. Most known fossils are from theMiocene, although a few unidentified forms are consideredPaleocene and two reportedly date to as early as the LateCretaceous.[4] Fossils of a living species ofColossoma from the Miocene have been described, suggesting a very conservative history for a specialized herbivorous fish.[5] All serrasalmine genera had originated by the middle Miocene, with the possible exception of three of the four piranha genera (Pygocentrus,Pristobrycon, andSerrasalmus).[4]
Many serrasalmids are in demand asaquarium ornamentals, and several pacus, such asPiaractus andColossoma, are economically important to commercialfisheries andaquaculture.[6]
Piranhas are generally less valued, although they are commonly consumed bysubsistence fishers and frequently sold for food in local markets. A few piranha species occasionally appear in the aquarium trade, and, in recent decades, dried specimens have been marketed as touristsouvenirs.[6] Piranhas occasionally bite and sometimes injure bathers and swimmers, but serious attacks are rare and the threat to humans has been exaggerated.[6] However, piranhas are a considerable nuisance to commercial and sport fishers because they steal bait, mutilate catch, damage nets and other gear, and may bite when handled.[6]