Red bellied piranha – Pygocentrus nattereri

Red-bellied piranha. Image: Wikipedia

Infamous predators reveal more bark to their bite

What do we talk about when we talk about piranhas?  Huge teeth? Voracious appetites?  Frenzied feeding shoals?  All fascinating, and all true.  However, a new study by Belgian scientists has shown that one species of piranha has a similarly curious (and previous undocumented) characteristic: the ability to create an amazing, complex range of sounds.

Sandie Millot and colleagues at the University of Liege in Belgium used underwater microphones to record a shoal of piranhas during a range of different behaviours such as aggression, intimidation, food competition and chasing (all characteristics we’ve come to expect from Hollywood depictions of the fish…!).  Fascinatingly, the researchers found that the piranhas produced different, distinct sounds depending on their behaviour (play the audio below!).

The clip features three sounds.  The first is a “bark” produced in what the researchers called a “frontal display”, meaning where two fish swam quickly towards each other and stayed still, aggressively intimidating and staring at each other.  The second is a “drum beat” produced by the largest fish in the group when circling the shoal, mostly when there was competition for food.  The third “croak” was generally associated with a piranha chasing and biting another fish.

How the sounds are produced

The sounds are produced by the piranhas using their swimbladder – an organ which helps keep the fish buoyant and stable in the water.  The piranhas vary the sounds produced by quickly contracting muscles leading the swimbladder.  The rate at which the muscles contract varies the sound produced.

A fearsome reputation. A close up of the piranha's impressive teeth. Image: ARKive

Why is this important?

The piranhas in the study were silent for most of the time, only producing these weird and wonderful sounds during (very aggressive…!) social situations such as group feeding.  What this research shows, that hadn’t been seen (or heard) before, was that sound is a key part of how shoals of piranhas interact with each other.  The fact that all the sounds produced were associated with aggression only serves to reinforce the reputation of this fearsome little freshwater predator!  In fact, one of the researchers suffered a serious bite to their finger from the piranha when carrying out the recording…

Where does the red-bellied piranha live in the wild?

In the wild, the red-bellied piranha is native to the freshwater rivers of South America, congregating in large shoals.  Whilst the fish has a reputation for its aggressive feeding, it rarely feeds in groups, instead individually preying on fish and molluscs.  However, under conditions of extreme stress, the piranha shoals will exhibit a spectacular ‘feeding frenzy’ if presented with suitable food, potentially stripping a large item of prey to the bone in minutes.

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2 Comments (+add yours?)

  1. The Naturette
    Nov 07, 2011 @ 23:44:03

    I loved watching these guys at the National Zoo (well, I can’t remember which type of piranha they have in the Amazonia exhibit). They were a lot smaller than I thought they’d be!


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