Something or someone that grunts, or any of various fish that make grunting sounds using their teeth and pharyngeal bones.
From grunt (verb) plus the agent suffix -er, meaning "one who grunts." The fish meaning comes from the actual sounds they produce underwater.
Grunter fish are named onomatopoetically and can literally "speak" to each other using sounds so distinctive that ichthyologists can identify species by audio alone—it's like their underwater Morse code.
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