The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with kettle of fish
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