Friday, October 16, 2015

Red-bellied Piranha (Pygocentrus nattereri): The World's Most Misunderstood Fish, by Don Orth

Sharp teeth, bright red belly, and grey and silver flecked scales on a laterally compressed body -- these characterize the Red-bellied Piranha.   That's one way to describe it.  Teddy Roosevelt in Through the Brazilian Wilderness referred to them as “most ferocious fish in the world.”    Since his book was widely read, many people were aware that the piranha  …will snap a finger off a hand incautiously trailed in the water; they mutilate swimmers—in every river town in Paraguay there are men who have been thus mutilated; they will rend and devour alive any wounded man or beast; for blood in the water excites them to madness. They will tear wounded wild fowl to pieces; and bite off the tails of big fish as they grow exhausted when fighting after being hooked.”  Ever since the cult film, Piranha, appeared in 1978,  frenzied feeding attacks cause otherwise sedate mid-westerners to scream “Piranha!”  In one segment of the film, the resort owner impatiently asks “What about the #$%* piranha?”   in reply, the manager deadpans  “They’re eating the guests sir.”    Hilarious!   No fewer than six movies on Piranha have been released for modern audiences.   Check one out at the nearest Redbox this weekend! Just don't expect more than 2 stars.

After witnessing Red-bellied Piranha feeding on helpless goldfish in a fish tank, every 12-year old boy wants one.   Feeding behavior in captivity was meticulously described by Fox (1972).  Each day he observed the attacks of the Red-bellied Piranha on a much large goldfish.   In 88% of feeding trials, the piranha attacked the tail.  Other attacks were on the eyes of the goldfish.  Both strategies quickly reduce mobility of the prey.   By the way, it is unlikely that that experiment would be approved by your Institution's Animal Care and Use Committee today.  The aggressive frenzied feeding is the primary mystique of the Red-bellied piranha, popularized by stories of a man’s face being eaten off, piranhas eating a duck, and many more frightening stories.  But, there is much more to this fish than what you view on Jeremy Wade’s River Monsters.  
Red-bellied Piranha.  Photo by Greg Moine.
The Red-bellied Piranha is certainly a devout carnivore and preys on much larger prey.  The Red-bellied Piranha is the best known of the piranha species.  The Red-bellied Piranha is a member of the large and diversified family  of fishes that includes the tetras, silver dollars, South American trout (Characiformes, Characidae).   The pacus, silver dollars and prianhas form a subfamily named Sarrasalminae with 80 species.        Although not all piranhas are carnivores, the name piranha actually means “tooth fish” in the Brazilian language Tupí.  The Wimple Piranha Cataoprion mento actually feeds on the scales of other fishes.  Yes, it’s a real mode of feeding called lepidophagy.
The Red-bellied Piranha is widely distributed in the freshwater tropical rivers of South America.   Of the 30 or more Piranha species, it is the one most commonly sold in the tropical fish industry.    However, this is not a beginner's fish.   It is a shoaling fish and will do better in a tank with many other Red-bellied Piranhas and, therefore, you must have a very large aquarium to keep the species.   Many Red-bellied Piranhas quickly outgrow their keeper’s fish tanks.  That cute little 1-inch piranha will easily grow to 6 inches in a year with proper care.  Consequently, many are released in waters of North America.  The released Red-bellied Piranha eventually will be caught by some bait-dunking fisherman.  Each year Piranha fears are arise as the Red-bellied Piranha , or it’s relative the Pacu,  Colossoma sp., is captured in some location river or lake. 

Earlier this year, a Red-bellied Piranha was caught by an angler in Lake Bentonville, ArkansasMany times the reports of a 3-6 pound piranha in a local lake go viral in the media.   Every time (Yes! Every damn time!) this turns out to be the vegetarian Pacu, a characid that grows to over 50 pounds.   Just look at the teeth!  Small pacu resemble the Red-bellied Piranha.   Just last month a 4-pound pacu was caught in a central Indiana lake.   
Close up photo displaying teeth of the Pacu (left) and the Red-bellied Piranha (right). Source.
Of all the tropical fish raised in the industry, the Red-bellied Piranha generates the greatest reaction in the way of state and local laws and ordinances prohibiting their sale and possession.    At least 24 states prohibit the possession and sale.  Many other cities also have ordinances prohibiting Red-bellied-Piranha.    The concern expressed by Teddy Roosevelt is evident today, as cattle ranchers and farmers are worried that a released Red-bellied Piranha will eat a cow (which locals did demonstrate for Roosevelt), or eat the face or feet off of swimmers.    Many of the fishes that co-evolved with Red-bellied Piranha have behavioral or morphological defenses to minimize or prevent attacks.  Our native fishes (and humans, of course) have no such defenses against attacks by the Red-bellied Piranha. 
States that prohibit possession of Piranha.  Sourc:
Most reports of the Red-bellied Piranha are based on a single fish captured and these are often only 3-6 inches.   For example, in Virginia, the only Red-bellied Piranha was a single 6-inch specimen taken from Indian Lake, a borrow pit in the Virginia Beach area (Stone 1987).  In most states, it is unlikely that the Red-bellied Piranha can survive over winter.   Cold-winters are the climatological tool in preventing establishment of invading populations of Red-bellied Piranha.    They do spawn readily in captivity and at temperatures common in many North American waters.  The risk that released Red-bellied Piranhas will establish populations is much greater in southern states.  The minimum temperature that kills a Red-bellied Piranha can be determined in lab studies.  One such study by Bennett et al. (1997) suggests that it is very likely Red-bellied Piranha can be established in waters of southern California, Texas, and Florida, although there is considerable year-to-year variability in winter severity. Two cases are known.   In 1993, officials in Hawaii located and destroyed an outdoor breeding operation for Red-bellied Piranha.   In 1977, officials in Florida eradicated a population of a different species of Piranha near Miami; this population persisted 13 years before its eradication. 
Map of likelihood of the Red-bellied Piranha overwintering. Bennett et al. (1997).

The Red-bellied Piranha is an important and fascinating part of the aquatic community in its native range.  Some of the observations on captive Red-bellied Piranha's informs our understanding of its role and life history.   Spawning behavior is described mostly based on captive specimens.  There are not  too many biologists snorkelling to observe Red-bellied Piranha in their native habitats that are murky with limited visibility. But see the video of Jeremy Wade with PiranhaSounds made by the Red-bellied Piranha are a critical means for their communication. Red-bellied Piranha use
fast sound producing muscles to contract tendons along the swim bladder (Millot and Parmentier 2014).  Red-bellied Piranha use sound for communication though the specific nature of this communication is still largely unstudied.   Because of the murky nature of their native habitats, communication helps individuals in shoals to find mates and share food locations.   Red-bellied Piranha seem to shoal in similar size groups, with smaller ones in floating meadows and largest specimens moving to marginal vegetation. 

Habitats used by different sizes of Red-bellied Piranha. Duponchelle et al. (2007)
The present diversity of piranha derived from a common ancestor that swam in the proto Amazon-Orinoco river drainages 9 million years ago.  Sea level changes and river basin and geological differences created many opportunities for unique types of piranha to speciate.   It is unlikely we can even begin to speculate how the Red-bellied Piranha might adapt if established in the Southern United States because so few populations have been studied to describe basic life-history.   In one of the few studies, Duponchelle et al. (2007) were surprised to find that females spawned at least twice during each breeding season in the Bolivian Amazon.   In the white waters of the Brazilian Amazon, the Red-bellied Piranha had two reproductive seasons per year (Queiroz et al. 2010).  The Red-bellied Piranha likely adjust their reproductive strategy to the availability of food in their environment.  
Number of larvae (vertical gray bars) and frequency of mature gonads (solid line) by month.  Horizontal lines represent high water (solid black) and low water (open bars).  Queiroz et al. (2010).
In closing, the Red-bellied Piranha is not a fish to be taken lightly and its commerce and risk of release will continue to keep us on high alert for newly established populations.  Most guides to tropical fish keeping list the Red-bellied Piranha among the fishes to avoid.   A solitary Red-bellied Piranha will be a boring fish to keep and they are not suited to a community aquarium.  Since its danger to humans has already been greatly exaggerated, I refrained from describing attacks that resulted in loss of digits, or other body parts including male genitalia because the movies are scary enough.  
Where possession is legal, Red-bellied Piranha can be maintained and even bred in captivity and will live for many years.    Before you commit to raising the Piranha, read the Complete Pet Owner's Guide.   In addition to responsible husbandry the Red-bellied Piranha should never be released. Euthanize unwanted specimens and deposit them in a natural history museum.       

Fascinated with the most misunderstood fish?  If you want to learn more, visit the only educational website dedicated to the Piranha and its close relatives


Bennett, W.A., R.A. Currie, P.F. Wagner, and T.L. Beitinger.  1997. Cold tolerance and potential overwintering of the Red-Bellied Piranha Pygocentrus nattereri in the United States.  Transactions of the American Fisheries Society 126(5):841-849.

Duponchelle, F., F. Lino, N. Hubert, J. Panfili, J.-F. Renno, E. Baras, J.P. Torrico, R. Dugue, and J. Nuñez. 2007. Environment-related life-history trait variations of the red-bellied piranha Pygocentrus nattereri in two river basins of the Bolivian Amazon. Journal of Fish Biology 71:1113-1134.
Fox, R.M. 1972. Attack preferences of the red-bellied piranha (Serrasalmus nattereri).  Animal Behaviour 20(2):280-283. 

Janovetz,  J.  2005.  Functional morphology of feeding in the scale-eating specialist Catoprion mento.  The Journal of Experimental Biology 208:4757-4768.

Millot, S., and E. Parmentier.  2014.  Development of the ultrastructure of sonic muscles: a kind of neoteny?  BMC Evolutionary Biology 14:24 

Queros, H., and A.E. Magurran. 2005.  Safety in numbers?  Shoaling behaviour of the Amazonian red-bellied piranha.  Biology Letters 1:155-157.  

Schleser, D. 2008. Piranhas: Complete pet owner's manual.  Barron's Educational Series.  96 pp.

Stone, S. 1987. 6-inch piranha found in pit at Indian Lakes. Virginia Pilot and Ledger Star, 23 August 1987.

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