mackerel Idiom, Proverb
holy mackerel
used to express strong feelings of astonishment, pleasure or anger "Holy mackerel," cried the little boy when he saw the new bicycle he got for his birthday.
Sprat to catch a mackerel
If you use a sprat to catch a mackerel, you make a small expenditure or take a small risk in the hope of a much greater gain.
holy Moses|Moses|cow|holy|holy cow|holy mackerel|m
interj.,
informal 
Used to express strong feeling (as astonishment, pleasure, or anger); used in speech or when writing conversation.
"Holy cats! That's good pie!" said Dick. "Holy cow! They can't do that!" Mary said when she saw the boys hurting a much smaller boy.