A study of red-bellied piranha (Pygocentrus nattereri) published in the Journal of Experimental Biology says that the carnivorous fish emit distinct sounds to ward off other piranhas when competing for food and space. University of Liège, Belgium biologist Eric Parmentier and study co-author Sandie Millot of University of Algarve in Portugal placed hydrophones in a tank housing three of the feared fish and observed their swimming behaviors as well as three distinct sounds that the fish made under certain conditions.
The researchers told National Geographic that the sounds included a repetitive grunt which they believe is a signal challenge to others, while a second sound that was akin to a low thud occurred when aggressive behavior and fighting was taking place. These sounds were created with a fast twitching muscle that contracts 100 to 200 times per second and runs parallel to the fish’s swim bladder. A third sound occurs from the fish grinding its teeth when chasing another fish.
Parmentier was aware that the fish were able to make audible noises but was not convinced on how the fish made the sounds, and wanted to define what the sounds meant to the other fish. Through constant observation, Parmentier was able to match the sounds picked up by the hydrophone with the physical movements of the piranha in the tank. Parmentier believes that the fish can make more than the three sounds observed in the fish tank and is hoping to travel to South America to record the red-bellied piranhas and other piranha species in their native environments.
The red-bellied piranha is one of the most feared fish known to man, likely due to its razor sharp teeth and movies depicting the fish in feeding frenzies in the rivers and waterways in which it lives. In reality though, the fish is generally a scavenger fish and not the menace portrayed in the movies. The fish grows to about 12 inches long and can weigh up to 7 lb.