Here's what we know:
* The imagery: The phrase conjures up the image of a fisherman hauling in a net full of fish, a “kettle” of fish, as it were. The phrase suggests a large, varied, and possibly messy collection of things.
* Early usage: The earliest recorded use of the phrase is from the 17th century, in a book of English slang. This suggests it was already a familiar phrase, implying it likely originated even earlier.
* Possible origins:
* Fishing: The most likely origin is that fishermen would catch a "kettle" of fish, referring to a large quantity of fish caught at once. This would then be used to describe any situation with a variety of elements, just like the diverse catch of a fisherman.
* Kitchen: Another possibility is that the phrase came from the kitchen, where a kettle of fish was a common way to cook fish. In this scenario, the phrase could refer to a variety of dishes prepared from a single source (the fish).
While the specific origin remains unclear, it's safe to say that the phrase "whole kettle of fish" has been around for centuries, and its use as a metaphor for a complex and varied situation continues to this day.