Fantastic fish brought to one worker (9)
I believe the answer is:
brilliant
'fantastic' is the definition.
'fish brought to one worker' is the wordplay.
'fish' becomes 'brill' (brill is a kind of fish).
'brought to' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'worker' becomes 'ant' (worker is a type of ant).
'brill'+'i'+'ant'='BRILLIANT'
(Other definitions for brilliant that I've seen before include "Excellent; a diamond" , "Exceptionally clever" , "Lustrous" , "Vivid; clever" , "Fantastic!" .)