Seahorses look like sweet, silent types, but high tech recording equipment finds that they growl when they are angry.

The discovery adds to growing body of evidence that many marine dwellers, even very tiny ones, are creatures with emotions and complex forms of communication to match. Seahorses already usually capture our attention, given their unique appearance and elegant way of moving in water.

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“They are cute, monogamous and calm fish, and people usually love them,” co-author Antonio Souto of Brazil’s Universidade Federal de Pernambuco told Discovery News.

People can love them too much, however, suggest the findings, which are published in the latest issue of the Journal of Zoology.

Lead author Tacyana Oliveira, Souto, and their colleagues equipped an aquarium tank with a hydrophone to capture audio recordings of seahorses during feeding, courtship and handling by humans.

The seahorses emitted happy-sounding clicks as they fed, with males and females both clicking away during courtship. As courtship heated up, so too did the clicks, which appeared to synchronize as the females and males grew closer to each other.

When a researcher would gently hold on to a seahorse’s body near the hydrophone, though, the equipment picked up a very angry sounding “growl.” This is the first time that anyone had ever detected such a sound coming from a seahorse.

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The researchers suspect that growls are also emitted when a predator holds on to seahorses in the wild.

The scientists wrote, “Seahorses are frequently grabbed and held by predators, such as frogfish, before being swallowed.”

They added, “Growls were accompanied by body vibrations, and may constitute an additional escape mechanism in seahorses, which might startle predators.”

Photo: A seahorse in the Black Sea. Credit: Florin Dumitrescu, Wikimedia Commons