IPA: //ˈɡrʌntər//
KK: /ˈɡrʌntər/
A type of fish that belongs to the family Terapontidae, known for making a grunting sound when caught, or a person who makes grunting noises.
The fisherman caught a grunter and was surprised by its unique sound.
Grunter is formed from "grunt" (from Middle English "grunten", meaning to make a low, guttural sound) and "-er" (meaning a person who). A grunter is a person or animal that makes a grunting sound.
Think of someone who makes a low sound ('grunt') — the '-er' indicates a person, so a grunter is someone who grunts.