What does "kettle of fish" mean?

Also, a fine or pretty kettle of fish. An unpleasant or messy predicament, as in They haven't spoken in years, and they're assigned to adjoining seats—that's a fine kettle of fish. This term alludes to the Scottish riverside picnic called kettle of fish, where freshly caught salmon were boiled and eaten out of hand. [Early 1700s]

a different or another kettle of fish. A very different matter or issue, not necessarily a bad one. For example, They're paying for the meal? That's a different kettle of fish. [First half of 1900s]