Fish tend to talk in one of two ways. Some use their bones: catfish make sounds by moving the vertebrae in their spine, while seahorses knock the bones of their skull together. Others, such as rockfish, quickly contract specialized sonic muscles around their swim bladder to make low-frequency grunting noises.
In primitive fish such as herring, the swim bladder is connected to the digestive system, so a sort of buzzing noise is produced when air is forced out the anus.
Flatulent herring have even been mistaken for Russian submarines.
LINK (via: Hakai Magazine)