Definition & Meaning of "holy mackerel"in English

What is the origin of the exclamation "holy mackerel" and how is it used?

Holy mackerel is an exclamation used to express surprise, amazement, or shock. It appeared in American English in the early 20th century, likely as a playful euphemism replacing "holy [something sacred]," with "mackerel" chosen for its alliterative sound rather than meaning. It was common in newspapers, cartoons, and everyday speech, especially in the 1920s–1950s, and became part of lighthearted or comic expressions of astonishment. Today it sounds old-fashioned, whimsical, or humorous, and is not considered offensive.