mach ghotI' is a Klingonese phrase which means "small fish". It is Klingon slang equivalent to "runt", "tiny", "small fry", etc., derisively referring to those considered excessively small in stature and weak in constitution.
The Klingon Gralmek was a mach ghotI', try as he might his body was never strong enough for him to succeed as a warrior, his diminutive statue did however make him an ideal candidate for Klingon Intelligence’s plans of espionage, surgically altering him to appear Human. (TOS - Blood Will Tell comic: "Beneath the Skin")
- This appears to be a word-by-word translation, and is a deviation from the normal grammar of tlhIngan Hol, where adjectives follow nouns; this would make "small fish" ghotI' mach. (tlhIngan Hol reference: The Klingon Dictionary)