Red-bellied Piranha

True to their name, red bellied piranhas have red undersides. Their head and bodies are various shades of  gray and flecked with bright , silver scales. Underneath their foreheads are powerful muscles that attach to a short , stout lower jaw fitted with triangular , razor-sharp teeth which are designed to bite down with incredible force. Although they are not visible from the outside, being covered by thick fleshy lips. Piranhas have large eyes , which contribute to their effectiveness as hunters. Red-bellied piranhas generally reach about 12 to 14 inches in length and weigh up to 3 to 4 pounds but depending on diet and habitat they can grow larger.

Piranhas thrive in warm, freshwater systems, including whitewater, blackwater, and clearwater rivers. They inhabit both fast-moving rivers and still waters like lakes and ponds . Although they prefer warm water, they can also survive in short periods of time in cooler waters. Piranhas are widely distributed in the neotropical fresh water rivers of Argentina, Brazil, Bolivia, Columbia, Ecuador, Guyana, Paraguay, Peru, Uruguay, and Venezuela.  Dense aquatic vegetation provides a good hiding spot and a consistent food source.

Red-bellied piranhas are very opportunistic eaters , meaning they eat what is available to them. Their diet shifts depending on the season. Contrary to the way media portrays them, they are not bloodthirsty killers, they are valuable scavengers, consuming dead or injured animals, which also helps keep the river clean.  They are mostly docile when well-fed and will avoid contact. Piranhas have a keen sense of smell, which is very useful in particular for detecting blood in the water, a strong attractant that can start a feeding frenzy. They have a line of sensors, similar to a lateral line, that allows them to detect subtle changes in water pressure and movement, signaling they presence of near by prey. As well as hear the splashing of a struggling  animal from a significant distance, which alerts them to a potential food source. Piranhas will hide in dark areas or vegetation and wait to ambush or chase their prey , lurking until an opportunity arrises.

Piranhas can eat about one-eighth of its own body weight in a day. They have a varied omnivorous diet, eating insects, aquatic invertebrates , crustaceans , small fish and dead animals. They also consume plant materials, such as seeds and fruits that fall into the water . A common feeding behavior is nipping fins from larger fish to get sustenance, rather than hunting the entire fish.  

Red-bellied piranhas travel in groups, called shoals ,meant to protect the group from larger predators . The younger fish are often on the periphery of the shoal, providing them with constant access to food and making them easier for adults to locate in the event of an attack. Piranhas communicate using sounds like barks , grunts, and clicks to signal aggression, stress or other social interactions. They also use body language , including specific postures and movements, to interact with each.  

During mating season, males display intensified red coloration. They also preform headstands and bite at the substrate as part of their courtship displays. Males build nests in the substrate and defend them territorially while guarding the eggs and attending to the female until they hatch. However, while generally social they can turn on each other and attack weaker to injured mates when food is scarce.

Besides themselves ,red-belled piranhas have numerous predators including river dolphins, caimans, larger fish and water snakes. They are a common food source for these animals.