In summary, Canadian and UK researchers have discovered that herring create underwater fart noises, suggesting they communicate by breaking wind. Some experts say that the digestive gases of fish are consolidated with their feces and expelled in gelatinous tubes (which fish then eat!), while others say that farting is a socially inappropriate way for fish to communicate. There is still some debate over whether or not fish fart, but it seems that everyone can agree that this is an interesting topic.

Reference: https://www.physicsforums.com/threads/do-fish-fart-controversy-and-research.72695/