Wednesday, February 11, 2015

The Red-Bellied Piranha: Deadly or Friendly

By: Hannah 
            What do you think of when you hear the word piranha? According to Sue Anne Zollinger in “Piranhas – Ferocious Fighter or Scavenging Softie?” most people think of the horror films version of piranha, fish with large, sharp teeth tearing a person apart after they fall into the water. Red-Bellied Piranhas are more than what is seen in a horror movie.
            According to Wikipedia, Seriously Fish, and WAZA (World Association of Zoos and Aquariums), the scientific classification for Red-Bellied Piranha is that they belong to the Family: Animalia, Phylum: Chordata, Class: Actinopterygii, Order: Characiformes, Family: Serrasalnidae, Genus: Pygocentrus (pygocentrus meaning ‘tail’ and kentron meaning ‘sharp point’), Species: P. nattereri (nattereri for an Australian naturalist from the 1800’s). They belong to the same family as pacu and tetras. They are fresh water fish that are omnivorous, scavengers.
            Red Bellied Piranha gets their name because their bellies are red. They also have broad, serrated, triangular, razor sharp teeth that make slicing chunks of fish free. Animal World said that red bellied piranha can reach up to 13 inches in the wild, but are smaller in an aquarium. The website Bristol Zoo said that red bellied piranhas can weigh up to a maximum of 3.5 kg. Baby red bellied piranhas have silver bodies with dark blotches. Red bellied piranhas get blackish spots behind the gills and the anal fin is usually black at the base, while the pectoral and pelvic fins vary from red to orange. It was also noted that males have a darker red belly than females.
            According to Seriously Fish, Wikipedia and Animal World, red-bellied piranhas live in tropical freshwater areas. These fish have a wide distribution throughout the Amazon and Orinco Basin Rivers in South America. Red-bellied Piranhas are found to be an abundant component of the fish in the Mamiraua Sustainable Development Reserve on the flooded forest of the Amazon River according to Magurran and Queiroz. They have also been found in the waters of major rivers, like Rio Paraguay. They have also been found in white water streams of South America. The water in these areas is about 15 to 35 degrees Celsius.
            Although red-bellied piranha have been portrayed, in horror movies, as being blood thirsty killers who eat large animals and humans who stray into the water, they are actually omnivores and scavengers. Large piranha hunts for food in the dawn, late afternoon and early evening. Younger, smaller piranha hunts for food during the day and hide from the larger piranha that would eat them. According to Animal World, red-bellied piranhas are not picky eaters. Red-bellied piranhas tend to eat fish, molluscs, insects, crustaceans, snails, algae and other water plants. According to Seriously Fish, they will attack sick or dying fish, feed on fins from larger fish and scavenge carcasses. They will hide and chase some fish from vegetation in shallow waters. It is during the dry season, when food is scarce that shoals of piranha are known to attack and have feeding frenzies. It is rare, according to Magurran and Queiroz, for piranhas to attack large, healthy prey.
            According to Edda Kastenhuber and Stephan C. F. Neuhass, red-bellied piranhas can produce a wide variety of acoustic sounds. Red-bellied piranhas can use phonetic language such as “hums, growls, grunts, boat whistles, hoots chirps and many other sounds.” The red-bellied piranhas have two basic mechanisms to help generate sound. They use muscle contractions, a displacement in the swim bladder and a clicking of bony parts like teeth and fins. Sound making fish vocalize in a seductive manner during courtship and mating season. They make sounds to aggressively defend their territory and also for alerting to danger in their shoals. But it was noted that most of the vocalizations were heard only when the piranhas were captured in a hand or a net.
            According to Wikipedia, Margurran and Queiroz, some of the breeding habitats of the red-bellied piranha are unknown to researchers. Researchers say that red-bellied piranha behavior in nature has revealed certain behavioral patterns around their nesting sites. Adult piranhas will swim side by side in a small circle, sometimes swimming opposite directions. One female piranha can lay up to 5,000 eggs, which the male and female piranhas defend until the eggs hatch. Up to 90% of the eggs survive.
            Red-bellied piranhas form into shoals where the bigger piranhas are in the middle and the smaller piranhas are on the outside. According to Webster Dictionary, shoals are a pack of piranha all grouped together. According to Magurran and Gueiroz, red-bellied piranhas find their mates in their shoals. Their decision on who is in the shoal is based on the size of the piranhas. They also choose their mates depending on the sizes. When the water is high in the rivers, a shoal can reach up to 30 individual piranhas. Large red-bellied piranha showed a strong preference for large shoaling partners, while the smaller piranhas did not have a preference in the sizes of their partners.
            Red-bellied piranhas are known for their reputation for being ferocious carnivores.  According to Seriously Fish, Wikipedia, and WAZA, the red-bellied piranha reputation is only a Hollywood movie myth. Red-bellied piranhas only attack people when it is the dry season or they are provoked. According to Seriously Fish, the myth began when American President, Theodore Roosevelt made a visit to the Amazon in Brazil in 1913 and he witnessed an attack. Then a movie was made called “Piranha,” by Joe Dante, which has been compared to “Jaws.” These films and stories of large Piranha shoals attacking humans, just fuel the exaggerated and erroneous reputation of piranhas.
            During my research, I read a few articles where red-bellied piranhas were dumped into other fresh waters and then attacked humans. But these waters would become too cold for the piranhas to survive and were more than likely dumped from someone’s aquarium. It is because of these rare attacks and the fact that only a very well trained person should handle them, that the piranhas myth continues today.

Works Cited: – Red Bellied Piranha
Katenhuber, Edda; Stephan, C. F. Neuhauss; 20 December 2011, Current Biology;
Magurran, Anne E; Helder L. Queiroz; University of St. Andrews, Scotland, “Partner Choice in Piranha Shoals”
The Nature Conservancy
Putz, Brian, University of Michigan-Ann Arbor, “Pygecentrus Nattereri Red Bellied Piranha,” 10/17/2012
Queiroz, Helder Lima; Marcela B. Sobanski; Anne E. Magurran; “Reproductive strategies of Red-Bellied Piranha (Pygocentrus nattereri Kner, 1858) in the white waters of the Mamiraua flooded forest, central Brazilian Amazon”
Seriously – Red Bellied Piranha
University of Zurich, Institute of Molecular Life Sciences; Neuroscience Center Zurich and Center for Integrative Human Physiology, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland, Current Biology, “Acoustic Communication: Sound Advice from Piranhas” – Red Bellied Piranha
Wikipedia: Red Bellied Piranha
Zollinger, Sue Anne, “Piranha – Ferocious Fighter or Scavenging Softie?” 3 July 2009

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