Sushi chefs divide all fish into three basic categories: red, white, and blue.How could I not dig for more information?
...Blue refers to fish that have silvery-blue skin, such as mackerel....Because the skin of these fish is silvery, sushi chefs also call them hikari mono, or "shiny things."
Sushi chefs began categorizing fish by color and shine in the early 1900s. Historians think that geishas in Tokyo's entertainment district may have been the first to popularize these categories by using them when dining with their clients. In Tokyo today, young people use a variation of the term "shiny fish" as a form of slang. They refer to girls who wear glitter and shiny clothes as "mackerel gals" because they look like shiny-skinned fish. In fact, mackerel have a reputation the world over for their ostentatious shine. In England, calling a man a "mackerel" meant he was a dandy; in France, it meant he was a pimp. It is from the latter usage that we get the term "mack daddy." (p. 154)
From the Dictionary of American Slang:
From Urban Dictionary:
mack n by 1887 A pimp; =mackman: …copped you a mack—Donald Goines [fr 15th-century mackerel, “pimp,” fr Old French macquerel, perhaps related to Dutch makelaar, “trade, traffic,” hence ultimately to make, macher, etc]
mac1 n by 1940s A mackintosh raincoat: His simple dream of naked girls in wet macs
mac2 n by 1928 Man; fellow; =buster, jack ●Used in direct address, often with a mildly hostile intent: Take it easy, mac [fr the many surnames beginning with Mac or Mc]
mackerel See holy cats
mackman 1 n black by 1950s A pimp; =mack: …went back to…that young mackman?—C Cooper …a mere player masquerading as a mack-man—Village Voice 2 modifier: …for all his jackass mackman shit—Village Voice
Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.
Class VI. Words Relating to the Sentient and Moral Powers
Section IV. Moral Affections
4. Moral Practice
procurer, pimp, pander or pandar, bawd, conciliatrix [L.], procuress, mackerel [archaic], wittol [obs.].